Winter-Kill Temperatures of Cold-Hardy Vegetables 2021

Our pond iced over.
Photo Ezra Freeman

Winter-Kill Temperatures of Cold-Hardy Vegetables 2021

I keep records of how well our crops do in the colder season, both outdoors and in our double-layer hoophouse. I note each increasingly cold minimum temperature and when the various crops die of cold, to fine-tune our planning for next year. We are in zone 7a, with an average annual minimum temperature of 0-5°F (-18°C to -15°C).

The winter 2020-2021 was mild, with our lowest temperature being a single late January night at 10°F (-12°C). We had one night at 11°F (-12°C) one at 17°F (-8°C), three at 18°F (-8°C also) and one at 19°F (-7°C). very little snow or ice. Similar to temperatures in the 2019-2020 winter.

The winter of 2018-2019 had lowest temperatures of 6°F (-14°C) in late January 2019, 8°F (-13°C) in December 2018 and a couple of 11°F (-12°C). In early January 2018, we had some extremely cold temperatures of -8°F and -9°F (-22°C and -23°C). Averaging our winter low over those four winters 2017-2021 gives 4.8°F (-15°C), within the zone 7a range.

Georgia Cabbage Collards, good down to 20F (-7C) Photo Southern Exposure Seed Exchange

New Info this winter

I’ve added in some temperatures for collard varieties (Georgia Cabbage collards, McCormack’s Green Glaze, variegated collards) from the Heirloom Collards Project, and also gained some info on spinach (Long Standing Bloomsdale), kales (Rainbow Mix Lacinato) and mustards (Chinese Thick-Stem) from Southern Exposure Seed Exchange. I’ve added in their suggestions on cold-tolerant early spring lettuces, Crawford, Simpson Elite, Susan’s Red Bibb and Swordleaf.

My results from other years still hold up.

Swordleaf lettuce on the right with another lettuce and radishes in spring.
Photo Bridget Aleshire

Using the List

Unless otherwise stated, these are killing temperatures of crops outdoors without any rowcover. All greens do a lot better with protection against cold drying winds. Note that repeated cold temperatures can kill crops that can survive a single dip to a low temperature, and that cold winds, or cold wet weather can destroy plants quicker than simple cold. Crops get more damage when the weather switches suddenly from warm to cold. If the temperature drops 5 or more Fahrenheit degrees (about 3 C degrees) from recent temperatures, there can be cold damage. The weatherman in Raleigh, NC says it needs 3 hours at the critical temperature to do damage. Your own experience with your soils, microclimates and rain levels may lead you to use different temperatures in your crop planning.

Reflect spinach in the open got damaged but not killed at -9F.
Photo Pam Dawling

Outdoor killing temperatures of crops (unprotected unless stated)

35°F (2°C):  Basil.

32°F (0°C):  Bush beans, some cauliflower curds, corn, cowpeas, cucumbers, eggplant, limas, melons, okra, some pak choy, peanuts, peppers, potato vines, squash vines, sweet potato vines, tomatoes.

27°F (-3°C): Many cabbage varieties, Sugarloaf chicory (takes only light frosts).

25°F (-4°C): Some cabbage, chervil, Belgian Witloof chicory roots for chicons, and hearts, Chinese Napa cabbage (Blues), dill (Fernleaf), some fava beans (Windsor), annual fennel, some mustards (Red Giant, Southern Curled) and Asian greens (Maruba Santoh, mizuna, most pak choy, Tokyo Bekana), onion scallions (some are much more hardy), radicchio, rhubarb stems and leaves.

22°F (-6°C): Some arugula (some varieties are hardier), Bright Lights chard, endive (Escarole may be a little more frost-hardy than Frisée), large leaves of lettuce (protected hearts and small plants will survive colder temperatures).

20°F (-7°C): Some beets (Bulls Blood, Chioggia,), broccoli heads (maybe OK to 15°F (-9.5°C)), some Brussels sprouts, some cabbages (the insides may still be good even if the outer leaves are damaged), some cauliflower varieties, celeriac, celtuce (stem lettuce), some collards (Georgia Cabbage Collards, variegated collards), some head lettuce, some mustards/Asian greens (Tendergreen, Tyfon Holland greens), flat leaf parsley, radicchio (both Treviso and Chioggia), radishes (Cherry Belle), most turnips (Noir d’Hiver is the most cold-tolerant variety).

Large oat plants will get serious cold damage. Oats seedlings die at 17°F (-8°C)

Canadian (spring) field peas are hardy to 10-20°F (-12 to -7°C).

Ruby chard, good down to 15°F (-9.5°C). hardier than Bright Lights, but less hardy than green chard varieties.
Photo Kathryn Simmons

15°F (-9.5°C): Some beets (Albina Verduna, Lutz Winterkeeper), beet leaves, some broccoli and cauliflower leaves, some cabbage (Kaitlin, Tribute), covered celery (Ventura), red chard, cilantro, fava beans (Aquadulce Claudia), Red Russian and White Russian kales, kohlrabi, some lettuce, especially medium-sized plants with 4-10 leaves (Marvel of Four Seasons, Olga, Rouge d’hiver, Tango, Winter Density), curly leaf parsley, rutabagas (American Purple Top Yellow, Laurentian), broad leaf sorrel, most covered turnips, winter cress.

12°F (-11°C): Some beets (Cylindra,), some broccoli perhaps, some Brussels sprouts, some cabbage (January King, Savoy types), carrots (Danvers, Oxheart), most collards, some fava beans (mostly cover crop varieties), garlic tops if fairly large, Koji greens, most fall or summer varieties of leeks (Lincoln, King Richard), large tops of potato onions, covered rutabagas, some turnips (Purple Top).

10°F (-12°C): Covered beets, Purple Sprouting broccoli for spring harvest, a few cabbages (Deadon), chard (green chard is hardier than multi-colored types), some collards (Morris Heading can survive at least one night at 10°F), Belle Isle upland cress, some endive (Perfect, President), young Bronze fennel, Blue Ridge kale, probably Komatsuna, some leeks (American Flag (Broad London), Jaune du Poiteau), some covered lettuce (Pirat, Red Salad Bowl, Salad Bowl, Sylvesta, Winter Marvel), Chinese Thick-Stem Mustard may survive down to 6°F (-14°C), covered winter radish (Daikon, China Rose, Shunkyo Semi-Long survive 10°F/-12°C), Senposai leaves (the core of the plant may survive 8°F/-13°C), large leaves of savoyed spinach (more hardy than smooth-leafed varieties), Tatsoi, Yukina Savoy.

Oats cover crop of a medium size die around 10°F (-12°C). Large oat plants will die completely at 6°F (-17°C) or even milder than that.

Garlic shoots poking through the mulch in January. Survive down to 5°F (-15°C), and if killed, will regrow from underground.
Photo Pam Dawling

5°F (-15°C): Garlic tops even if small, some kale (Winterbor, Westland Winter), some leeks (Bulgarian Giant, Laura), some bulb onions, potato onions and other multiplier onions, smaller leaves of savoy spinach and broad leaf sorrel. Many of the Even’ Star Ice Bred greens varieties and the Ice-Bred White Egg turnip are hardy down to 6°F (-14°C), a few unprotected lettuces if small (Winter Marvel, Tango, North Pole, Green Forest).

0°F (-18°C): Chives, some collards (Blue Max, Winner, McCormack’s Green Glaze), corn salad (mâche), garlic, horseradish, Jerusalem artichokes, Even’ Star Ice-Bred Smooth Leaf kale, a few leeks (Alaska, Durabel, Tadorna); some bulb onions, yellow potato onions, some onion scallions, (Evergreen Winter Hardy White, White Lisbon), parsnips (probably even colder), salad burnet, salsify (?), some spinach (Bloomsdale Savoy, Long Standing Bloomsdale,  Olympia). Walla Walla onions sown in late summer are said to be hardy down to -10°F (-23°C), but I don’t trust below 0°F (-18°C)

Crimson clover is hardy down to 0°F (-18°C) or perhaps as cold as -10°F (-23°C)

-5°F (-19°C): Leaves of overwintering varieties of cauliflower, Vates kale survives although some leaves may be too damaged to use. Lacinato Rainbow Mix kale may survive this temperature.

A cover crop mix of winter rye, hairy vetch and crimson clover.
Credit Kathryn Simmons

-10°F (-23°C) Austrian Winter Field Peas and Crimson clover (used as cover crops).

-15°F (-26°C) Hairy vetch cover crop – some say down to -30°F (-34°C)

-20°F (-29°C) Dutch White clover cover crops – or even -30°F (-34°C)

-30°F to -40°F (-34°C to -40°C): Narrow leaf sorrel, Claytonia and some cabbage are said to be hardy in zone 3. I have no personal experience of this.

-40°F (-40°C) Winter wheat and winter rye (cover crops).

Hoophouse Notes

Winter crops snug in our hoophouse in a December snowstorm.
Photo Pam Dawling

Our double-plastic hoophouse keeps night time temperatures about 8F (4.5C) degrees warmer than outdoors, sometimes 10F (5.5C) degrees warmer. Plus, plants tolerate lower temperatures inside a hoophouse. The soil stays warmer; the plants recover in the warmer daytime conditions (it seems to be the night+day average temperature that counts);

In the hoophouse (8F (4.5C) degrees warmer than outside) plants without extra rowcover can survive 14F (7.7C) degrees colder than they could survive outside; with thick rowcover (1.25oz Typar/Xavan) at least 21F (11.6C) degrees colder than outside.

For example, salad greens in our hoophouse can survive nights with outdoor lows of 14°F          (-10°C). Russian kales, lettuce, mizuna, senposai, spinach, tatsoi, turnips, Yukina Savoy survived a hoophouse temperature of 10.4°F (-12°C) without rowcover, -2.2°F (-19°C) with. Bright Lights chard got frozen leaf stems.

Lettuce Notes

Lettuce varieties for a solar-heated winter greenhouse or hoophouse in zone 7a: (hardiest are in bold) Buckley, Ezrilla, Green Forest, Green Star, Hampton, Hyper Red Rumpled Wave, Marvel of Four Seasons, Merlot, New Red Fire, North Pole, Oscarde, Outredgeous, Pirat, Red Cross, Red Sails, Red Salad Bowl, Red Tinged Winter, Revolution, Rouge d’Hiver, Salad Bowl, Sylvesta, Tango, Winter Marvel, Winter Wonderland.

Cold-tolerant early spring lettuces include Buckley, Crawford, Green Forest, Hampton, Merlot, New Red Fire, Revolution, Simpson Elite, Susan’s Red Bibb and Swordleaf.

Notes on Chicories and Endives

Verona Red radicchio, hardy to about 20°F (-7°C).
Photo Southern Exposure Seed Exchange

Chicories and endives fall into two groups, but they are confusing because the common names sometimes suggest the opposite group than they are botanically. Here’s the best info I have.

Cichorium intybus, commonly called chicories, are mostly heading crops. The group includes radicchio, both Treviso and Chioggia – hardy to about 20°F (-7°C). Belgian Witloof endive (the kind for forcing chicons) is also a chicory. It dies at 25°F (-4°C). Sugarloaf chicory is the least hardy chicory, and dies at 27°F (-3°C).

Cichorium endivia, commonly called endives, are mostly loose-leaf crops, less cold-hardy than intybus types (chicories). This group includes Frisée types and escaroles, which are also known as Batavian endives. They generally survive down to 22°F (-6°C), although Perfect and President endives can survive down to 10°F (-12°C) – can anyone confirm or deny this?

© Pam Dawling 2021


Go to my Events Page for more information on these online events

Mother Earth News Fair Online: Food Independence Course Part Two was released on 3/26/21.

It consists of eight video presentations, most of which come with pdf handouts. My contribution is Growing Asian Greens, and pairs nicely with Guide to Asian Vegetables with Wendy Kiang-Spray, author of The Chinese Kitchen Garden: Growing Techniques and Family Recipes from a Classic Cuisine. Other topics include Dandelion Wine, Homemade Teas, Food Conversations, Passive Solar Greenhouse Design, Productive Growing from Home, and Growing Your Own Spices.

You can subscribe to the All-Access Bundle for $2.99/month (or $35 for a year).

My previous contribution is an 8-part Garden Planning Course

I also did a workshop on Winter Cover Crops for Gardeners as part of the Winter Gardening Course.

All these and many more videos and handouts are available as part of the All-Access Bundle.

 

Root Crops in February

 

Large Smooth Prague celeriac. (Currently sold out Feb 2021)
Photo Southern Exposure Seed Exchange

Root Crops to Plant in Central Virginia in February

We sow no root crops in our hoophouse in February. It’s too late for radishes or turnips. If you are in a place colder or darker than winter-hardiness subzone Zone 7a, with an average minimum temperature of 0° to 5° F (-18°C to -15°C), see Root Crops in January.

If the soil outdoors is dry enough and not frozen, we spread compost on the raised beds we plan to plant in February and March, and till in the compost. Root crops that we sow outdoors here in February include carrots #1 and turnips in mid-February, and carrots #2 and radishes in late February. It’s true not much growing happens in February, but it helps us if we are able to get some crops planted early, leaving us more capacity for other crops once those are in the ground. And if the soil isn’t dry enough, we just do those jobs as soon as we can. We would hate to miss an opportunity!

Carrot Bed Prep

One of our many carrot beds, looking good.
Photo Kathryn Simmons

Carrots do very poorly with competition from weeds or too many other carrots. You can make use of the Stale Seedbed Technique, preparing the bed ahead of time, and flaming or hoeing one or more flushes of weeds as they germinate. I’ll do a separate blogpost on flame-weeding soon, as I have too much info to squeeze in here. It works so well, it feels like cheating!

Carrots are small seeds, needing a fine tilth (small soil particle size and good texture – not likely to crust or blow away).  Good information on crop spacing for maximum yields, or biggest vegetables is in an out of print book, The Complete Know and Grow Vegetables by JKA Bleasdale, PJ Salter, and others. For maximum total yield of carrots, they recommend 1.5” x 6” (4 x 15cm). You get medium sized carrots. For early carrots go with 4 x 6” (10 x 15cm) to minimize competition and get rapid growth. If you want to have rows more than 6” (15cm) apart, calculate the area of these optimum spacings, then divide by your chosen row space. For example, if your rows are 12” (30cm) apart, the carrots can be as close as 0.75’ (2cm) if total yield is more important than individual size, or 2” (5cm) for fast early carrots. We do five rows in a 4 ft (1.2m) bed, so the rows are about 10” apart, with the outer rows 4” (10cm) from the bed edge.

Young Carrot Plants After Thinning. Photo Kathryn Simmons

Carrot Thinning and Weeding

Remember to thin carrots as soon as you can see them well enough to do so. We usually hoe between the rows first, then crawl along thinning and weeding. It does take time! But you won’t get good carrots without thinning, unless you either have a precision-seeder that drops one seed per inch, or pelleted seed which you can sow at one per inch. Precision seeders like the Jang are expensive, but worthwhile if you need to use it every week. Pelleted seed costs more than raw seed, and its big advantage is traded off for two other disadvantages: The soil has to be kept well-watered until germination or else the clay coating will imprison the seed forever, and the seed does not store for long – don’t keep any over for next year.

Greenhouse Root Crop Sowings for Transplants

The only root crops we ever transplant are celeriac and kohlrabi (a stem vegetable really, not a root). I have transplanted many things and I am skeptical of books saying this or that can’t be transplanted, but not beets or rutabagas, which I hear people transplant as soil blocks or plugs. So try it if you think it will help.

Celeriac

Flats of celeriac seedlings.
Photo Kathryn Simmons

We have grown both Diamante (100 days from transplanting) and Large Smooth Prague (110d), and strongly prefer Diamante, as it seems to us to be more tolerant of warm weather, less prone to rot, and easier to clean. Several growers say that Diamante and Brilliant are virtually indistinguishable.

This crop likes rich soil with lots of organic matter, some shade from mid-day and afternoon sun, and ample water without sitting in waterlogged soil. We make sure to choose beds in a shadier part of the garden. Celeriac can rot if too damp, so keep it weeded and remove some of the lower leaves to improve airflow. A pH 5.8-6.7 is ideal. Celeriac can benefit from seaweed as a foliar spray, or side-dressing with compost during the long growing season.

Celeriac requires long steady growth, and the challenge is to prevent checks to growth. The Virginia climate is on the warm side for celeriac, it prefers cooler areas, but we have good success if we pay attention at a few critical times. Celeriac can tolerate frost quite well, so there is no hurry to harvest in the fall.

Sow seeds 1/8″(3mm) deep, and keep the soil surface moist. The minimum germination temperature is 40°F/5°C, and the optimal range 59–70°F/15-21°C. Germination is slow, typically 14 to 21 days, and it takes 10-12 weeks to grow to transplant size, so start in plenty of time. We sow in open flats, then spot out (prick out) into deeper flats. We sow February 10, which is about 10 weeks before our last frost date. Celeriac can be sown from 67 days before the last frost date to 184 days before the first fall frost date, but you don’t get large roots unless you have plenty of growing time.. If your climate includes long chilly springs, I’d suggest starting 12 weeks before the last frost date.

Emergence takes at least 12 days at 59°F/15°C and 7 days at 68°F/20°C. The ideal temperature is 68°F/20°C day, and 59°F/15°C at night. The fluctuating temperatures, with nights cooler than days by 9°F/5°C, help speed germination. Another factor when choosing germination temperature to aim for, is that at 59°F/15°C, only 40% of the seeds produce seedlings, compared to 97% at 68°F/20°C.

Celeriac should not be hardened off by reducing temperatures, as that can cause them to bolt. More than about 9 night temperatures below 55°F/12°C will cause bolting. Plants can have their watering reduced to help them get ready for the big outdoors. Use rowcovers if a cold spell arrives after you have planted them out, or if you know cold weather is likely to return. Falling apple blossom is a phenology sign that conditions are suitable.

See Root Crops in May for transplant info

See SESE’s Celery & Celeriac Growing Guide for growing information.

Kohlrabi

Harvested kohlrabi, Early White Vienna and Early Purple Vienna.
Photo McCune Porter

Kohlrabi is very easy to grow, treat it just like cabbage or kale.

It can be direct-seeded, but for an early crop, especially if you live in a climate like ours where spring turns into summer very quickly, use transplants. We don’t grow a lot, only 180 feet (55m) in total for 100 people. We also grow kohlrabi in the fall, transplanting bare root transplants from nursery seedbeds around August 3. We grow twice as much in fall as spring, because we can store them for winter.

We have grown both Early White Vienna and Early Purple Vienna. Growing both provides for pretty harvests. We sow February 8 at 4 seeds/inch (0.5 cm apart) in open seed flats, aiming to have the plants spotted out, hardened off and transplanted outdoors with rowcover on March 13. Fast work!

Root Crops to Harvest in Central Virginia in February

Hakurei turnips harvested late January.
Photo Pam Dawling

As for January, in central Virginia, there are normally no roots that we could be harvesting outdoors in February except parsnips, Jerusalem artichokes and horseradish.  We do have horseradish, but not the others. Of course, you can only dig up root crops if the ground is not frozen!

We have had outdoor night temperatures of 16°F/-9°C and 12°F/-11°C. This winter we have some carrots “growing” in the fresh air and some late-sown beets under rowcover. I don’t think we’ll get roots from the beets, but the leaves might make a nice change from brassicas as cooking greens.

In the hoophouse our radishes #3 (sown October 30) will come to an end by 2/1. Our #4 radishes will get harvested this month. Our #5 radishes, sown 12/23, will feed us from then until around April 7

We still have some of our first turnips (sown around October 13) until mid-February, and they have reached a really good size, thanks to early thinning. This month we can harvest the second sowing (October 25). We thinned turnips #2 in early January. They are looking good too.

Red Round turnips in our hoophouse in late January.
Photo Pam Dawling

We have not yet needed to unroll our inner rowcovers in the hoophouse. We wait until we expect it to get down to 8°F (-13°C) outdoors, as we like to avoid extra work!

Other Root Crop Tasks in Central Virginia in February

Potatoes stored in crates in our root cellar.
Photo Nina Gentle

Check stored vegetables

Stored crops need to be checked for decay at least once a month, preferably once a week now the days are getting longer and the temperatures will get warmer. From storage, we can eat beets, carrots, celeriac, kohlrabi, parsnips, potatoes, rutabagas, sweet potatoes, and turnips, if we grew them.

Special Root Crop Topic for February in Central Virginia

Wrap up the winter planning

Our garden planning wraps up by mid-February, with all the budgets, crew selection and shift decisions (afternoons in cold weather, mornings in hot weather –  we’re mostly half-day gardeners, with one or two stalwart all-day workers)

Order summer cover crop seeds

Buckwheat cover crop in flower.
Photo Pam Dawling

For early spring, if we find an area without a winter cover crop and we realize we won’t plant it with a vegetable crop for at least 8 weeks, we sow oats. They will smother weeds and add organic matter to the soil when you till them in.

If you have not already ordered summer cover crop seeds, this would be a good time to do so. Cover crops suppress weeds, add organic matter, feed the organisms in the soil and attract beneficial insects, birds and amphibians to feed and reproduce. Biodiversity encourages ecological balance that can help reduce plant diseases and pest attacks. Have a goal of No Bare Soil. Seek out odd spaces to fill with cover crops.

Once frosts are past, buckwheat is an easy cover crop. Its flowers attract beneficial insects, and it is a very manageable (not too tall) fast-growing crop. Buckwheat can be in and under in a month.

Just as fast is mustard, but we don’t grow that because it’s a brassica and we grow a lot of brassica food crops. Keeping a good crop rotation is important to us. Also we have harlequin bugs and we don’t want to feed them year round.

Sorghum-sudangrass hybrid is a fantastic, huge warm weather grass type cover crop, but don’t grow it if you have only a lawnmower, a scythe or a nylon line weed whip to cut it down! For smaller scale gardens, choose Japanese millet.

Soybeans, southern peas and sunn hemp are easy legume cover crops for warm weather, providing nitrogen for the next crop.

Cover cropping is a big topic. See my book Sustainable Market Farming for more. Here I’m just pointing you in the right direction enough to order seeds soon. You can read up more later.

Book Review: The Chinese Greenhouse, Dan Chiras

Book Review: The Chinese Greenhouse: Design and Build a Low-Cost, Passive Solar Greenhouse, Dan Chiras

New Society Publishers, 2021. 230 pages, color photos and diagrams throughout, $34.99.

I have been eagerly awaiting this book, after attending several of Dan Chiras’ workshops where he talked about the evolution of Chinese Greenhouses. This is a next step for those of us thrilled with what we can grow in a passive solar hoophouse. As we harvest our abundant winter greens, we might ponder “What if it were possible to grow warm weather crops in winter without fossil fuels, given a careful greenhouse design with attention to insulation and so on?” The Chinese Greenhouse provides the answers, design and construction tips for pioneers in this new kind of greenhouse. Don’t reinvent the wheel – get this book and learn from those who have gone before.

Chinese Greenhouses are not readily available off the shelf, and are best designed to suit the particular site. This book tells you, step-by-step, how to build your own. Naturally, building one of these high-performing structures is more work than putting up a standard hoophouse (high tunnel), but once you have put up one of those, you might be ready for more challenge (and rewards).

Chinese greenhouses are solar-heated, earth-sheltered, well-insulated, plastic-glazed structures, using heat-banking, and shaded and curtained when appropriate. They are always oriented with a long side facing the sun. In the winter, this allows maximum (low-angle) sun exposure. In the summer, the high arc of the midday sun goes over the roof, and crops don’t get baked. The energy-intelligent design reduces your carbon footprint and saves you from future fuel bills, or imported vegetables.

Dan identifies six design problems with standard greenhouses that are solved with Chinese greenhouses. If you have a standard greenhouse, you can modify it to reduce the impact of the short-comings, by adding water for heat storage, using compost as a heat source, or storing pumped hot air in pipes in the soil. Dan Chiras has tried some of those. Also see The Bio-Integrated Farm by Shawn Jadrnicek. Or you can keep your existing hoophouse for growing winter greens, and put up a Chinese greenhouse for winter tomatoes and citrus trees.

Enclosing the north (south in southern hemisphere) side in the ground (which is 50-55°F (10-13°C) below the frost line year-round) is an important feature of these Chinese greenhouses, helping stabilize the temperature. To grow warm weather crops you need to maintain a greenhouse minimum temperature of 40-50°F (4-10°C). These crops may survive lower temperatures, but they will not thrive or be productive.

A Chinese greenhouse with metal roof trusses and a heat-banking back wall. A path by the wall gives access for harvesting and tending to plants. Photo by Dr. Sanjun Gu, courtesy of Dan Chiras

Dan Chiras met Dr Sanjun Gu, a world authority on Chinese Greenhouses, in Iowa in 2014, and gathered the available information (it wasn’t much, most was in Dr Gu’s slides!). Chinese greenhouses emerged in the mid-1980s, as a way to feed the expanding population. There have been three generations of such greenhouses, and traditional materials such as bamboo posts and external straw mat night curtains have now been replaced by easier-to-use modern materials. The first generation Chinese greenhouses had a bowed roof framing of bamboo poles in a mesh of tensioned steel wires. This framing was supported by many posts, and plastic sheeting was stretched over the top. At night, straw matting was unrolled on top of the roof (effective but labor-intensive). The second generation design reduced the number of posts supporting the roof, allowing the use of small machinery to till the soil. Third generation Chinese greenhouses don’t need posts at all, but have curved steel roof trusses (bows).

Newer models have replaced the straw matting on the outside with synthetic insulated blankets, or with reflective curtains on the inside of the roof, and replaced the hours of manual adjustments with mechanization. There are now billions of acres of these greenhouses in China. About one-third of Beijing’s winter vegetables are grown in greenhouses (I’m unclear if that’s one third of all their vegetables, or one third of warm weather crops.)

Dan has logged winter indoor and outdoor temperatures at his home-built modified Chinese greenhouse in Missouri, and found an indoor minimum of 48°F (9°C) with outdoor temperatures of -10°F (-23°C) for the first two winters. One feature of this book that especially appeals to me is that Dan describes the pros and cons of multiple options for achieving various goals – thermal mass, insulation, glazing, trusses – no need for expensive mistakes!

To build your Chinese greenhouse, you first need to choose a site, excavate it and take steps to prevent water leaking into your greenhouse. Yes, you really do need to earth-shelter your Chinese greenhouse, unless you are in the southern tier of the United States. While you are planning your excavation, consider the options of geo-thermal heating/cooling tubes, or tubing to take excess hot air from the greenhouse and store it in the earth berm until winter.

Check the slope of your land and draw a scale plan to make sure it will work. The perfect slope is 20° south, but anywhere between 10° and 30° will work. It partly depends on the height you want inside. You can also import soil if you need more than your excavation will provide. Stake out the site, using a compass to get the best orientation, correcting for magnetic declination (it’s all in the book). Ensure you are not excavating in a natural drainage path – observe the path of heavy rainfall or snowmelt. Look for subsurface springs or seeps. Look for wet areas in spring. You don’t want to have to incorporate a “water feature” in your new greenhouse! Perhaps consult a water engineer or locally experienced excavator. If necessary, construct swales uphill from your site, to divert water away from your greenhouse. Details of these and various drainage possibilities are in the book.

Dan recommends renting a skid steer loader with tracks rather than tires, or a small excavator. Keep the topsoil and subsoil separate, and covered if it might rain before you finish. Get seed on hand to sow on the berm as soon as possible after creating it, and/or transplant native ground cover plants.

If you really can’t do earth-sheltering, you can compensate to some extent in an above-ground greenhouse by adding lots of thermal mass in the floors and walls. I have some mixed feelings about the use of interior thermal mass. In the 1970’s there were greenhouse books advocating so many barrels of water to store heat, that there was little space left to grow plants!

After completing the excavation you can start incorporating heat-absorbing dark colored thermal mass in the floor and back wall, up to the optimal 4” (10 cm) thick, to store heat gained during sunny days. Dan discusses several possible materials: poured concrete, bricks, flagstones, soil-cement, cement blocks, bin blocks, adobe, cob and rammed earth. How’s that for a thorough review of options? Beware earthen materials that can disintegrate in a damp environment (you can’t use them underground). An adobe, stone or blockwork north wall works. Be aware of all the ecological pluses and minuses of concrete. Bin blocks are large concrete blocks made by concrete contractors when emptying out returning concrete mixers. The price is good! Paying for transportation is expensive! The smallest ones weigh half a ton, so you’ll need at least a tractor with a bucket, if not a crane, to stack them.

If this sounds like a lot of work and you start thinking about installing a wood stove instead, Dan invites you to think again: wood heat is “the black sheep of the renewable energy field.” Burning wood produces carbon dioxide, contributing to global warming. It also produces toxins such as sulfur and nitrogen oxide gases, which form acid rain. And particulates that irritate lungs.

Author Dan Chiras.
Photo Dan Chiras and New Society Publishers

The next group of decisions is about wall framing and glazing. Will your framework be curved or in flat planes? Only some kinds of glazing curve, so figure these two items out together. Soil is not a good insulator, as many people wrongly assume. The water in the soil conducts heat, so it is important to insulate the north wall, north roof, and the east and west ends.  You’ll need deep walls with space for R-40 to R-50 insulation. Dan discusses options: loose-fill cellulose and fiberglass; batts of fiberglass, rock wool and cotton; rigid foam sheets of polystyrene, polyisocyanurate, and mineral wool board; liquid foams like Icynene and Air Krete. He recommends loose-fill cellulose, which is made from old newspapers.

Framework options include traditional lumber, home-made or purchased laminated wood rafters (straight or arched), steel tubing (round or square), or metal trusses. There are photos and tips for each of these. Be sure to consult a structural engineer or architect to ensure your roof will support the snow and wind loading that you might experience in your location. While tubing is adequate for smaller greenhouses, steel trusses are stronger and advised for wider greenhouses.

If you are using standard lumber and vertical walls, you will need to carefully determine the roof angle giving the best light transmission without too much summer heat gain. Light hitting the glazing at small angles will reflect rather than pass through. The rule of thumb is to add 20° to your latitude to get the ideal roof angle for maximum winter sun transmission. I found this particular sidebar confusing, but happily, I don’t need to know right now. Dan recommends a lower sloped roof than the calculation suggests, perhaps 30°.

Options for glazing include glass, ETFE, rigid polycarbonate, poly reinforced polyethylene sheeting, and polyethylene film. Light transmission ranges from 75-95%, but light transmission is not all we care about. Plants can do better with light diffused through translucent materials, bouncing around at all angles rather than beaming straight in. Glass is fragile and expensive.

The price of the plastics starts with a high for ETFE (ethylene tetrafluoroethylene), For most of us, this is outside the budget: $9,000 for a 20 ft (6 m) greenhouse. Sell 7,000 bags of lettuce to pay for it! Double-wall acrylic is another very pricey option, with very pricey shipping costs. Solawrap looks like bubble-wrap on steroids, provides some insulation (R-1.7) It is sold in rolls the width of the gap between bows (or rafters). A roll 4’ x 328’ (1.2 x 100 m) costs about $2,200 plus shipping. Polycarbonate has channels of air providing some insulation. The price is lower than Solawrap, but the special hardware adds to the cost. Poly reinforced polyethylene (PRP) resembles rip-stop fabric used for outdoor gear, with a reinforcing mesh embedded in it. It comes with a ten-year UV warranty. Avoid wearing holes in your PRP by fitting it snugly after duct-taping any hardware that will contact the sheeting. The price is one-tenth that of Solawrap (but it provides no insulation). Standard 6 mil greenhouse poly is much cheaper, and using two layers with an inflated air space provides some insulation. You’ll need to replace the plastic every 5-7 years.

Watch this YouTube of Dan Chiras talking about the Chinese Greenhouse

To reduce heat losses through the glazing at night, install a blanket. White shadecloth resting on plastic-coated cables or laundry line works well. Aluminet and Tempa Interior Climate Screen work even better as heat reflectors, keeping heat out in summer, in during the winter. Radiant heat barriers can be used on the inside surfaces of roofs and walls to reflect heat back. One kind is a shiny aluminized sheet with a scrim backing, another kind is reflective bubble wrap.

The next part of the book explains ways to improve on the performance of Chinese greenhouses, to consider before you start. Use the excess heat on sunny winter days to mitigate the cold night temperature. Hot air from the top of the greenhouse can be pumped into porous pipes running through an in-floor storage medium such as a bed of gravel. You can wire thermostatically-controlled low-wattage DC fans directly to 50-watt photovoltaic modules, without batteries. When the sun shines, the fans operate. Having air movement in a greenhouse is helpful in managing fungal diseases and bugs, even when it isn’t banking heat. And bringing hot damp air through a gravel bed allows condensation to form in the gravel bed, effectively reducing the humidity of the air above.

Seasonal heat banking is designed to store excess heat from the summer to use in the winter. The usual method is to construct a large heat exchanger, composed of lots of plastic pipe deep underneath the greenhouse. Underground heat at 7 m (23 ft) deep moves through the soil by conduction at a rate of 1 m (3.3 feet) per month. Another method (without pipework) is to install a skirt of rigid board insulation just underground, all around the building to 20 feet (6 m) out. This catches the heat escaping from the building as well as that coming up from deeper in the earth.

I’m going to slide right over the details of designing and building heat bank systems. They involve pumps capable of providing five air changes per hour, thermostats, fans, piping sufficient to allow an airflow rate of 5 feet (1.5 m) per second – that’s 3 mph! Before installing any expensive heat banking and recovery systems, talk with people already using such a system. Once you have literally sunk a lot of money underground, it is very expensive to change. “If you get it right, you should be able to create a structure whose internal temperature in the winter is a heart-warming 35-40 F higher than ambient temperatures.” And pleasant summers too.

Next we have a chapter on minimizing summertime heat gain. One aspect is the roof angle, which we already looked at. A design that works at one latitude won’t be as good at a location with different sun angles. You can shade, vent and (if not in a humid climate) mist, in order to cool the space. That should provide for an extended period of summer use, if not the whole of the summer. Your cooling efforts might need to be moderated by your bug-excluding efforts. You could build a pond (10-15 feet (3-5 m) deep) with cooling loops of pipe. That’s one improvement you can add after construction, adding a fan to spread the cooled air inside.

Next there is info about supplementing the lighting with LEDs, for cloudy areas, or if you are growing commercially. There are explanations about different wavelengths of light, which ones plants use, and in what proportions (65% red, 15% blue, 20% green), and about total PAR, photosynthetically active radiation, the proportion reaching your plants, and the varying PAR requirement at different stages of plant growth. Another consideration is the total amount of light the plants receive each day (the daily light integral).

The final chapter of the book is Dan’s illustrated description of building his Chinese greenhouse in Missouri. His goals are to be cost-effective and environmentally friendly. For simplicity, Dan chose a lumber vertical south wall and sloped (not arched) roof, a departure from the usual curved Chinese greenhouse look. It appears to be about 21 ft long and 30 ft wide/deep. He used 3ft x 16ft (1 m x 5 m) polycarbonate roofing sheets, with plastic H-profile connector strips.

Dan does not gloss over the problems he and his band of helpers met during the 2-3 years spent building his greenhouse. His site was only slightly sloped, so he needed to dig down till he hit bedrock at 6 ft (2 m), then build up and import topsoil to complete the berm. His greenhouse uses rammed earth-filled tires (two summers of work). This is a labor-intensive method, physically draining. Think twice. You’ll need sturdy friends to help you. Even Dan says he would make a different choice if he had it to do over.

There are photos of the gravel footings, the underground pipework, the thermal mass north side and end walls and their insulation, concrete foundations, the Herculean rammed earth tire walls, earth cooling tubes, L-bolts to anchor the tire walls to the sill plate for the glazing, waterproof membranes for the walls that will be in the ground, framing, roofing, and glazing. Keep the chickens from pecking your cob infill, the new berm, suitable groundcover plants, and foam insulation board! Finally a photo of the first plateful of spinach!

Dan ends the book with two of his newest ideas – wind scoops and a methane digester. Of course, all these engineering tweaks won’t help if you’re not a good plantsperson to start with, so you might brush up those skills too, with a different book.

Remember, these are the pioneering days for Chinese greenhouse builders and growers. Not everything has been figured out, especially for locations very different from China or Missouri. You can’t buy exactly what you need “off the shelf”. You have to figure out some things for yourself. Some ideas in this book are untested. Don’t take anyone else’s ideas as the perfect solution, This book would have benefited from a bit tighter editing to remove a few slip-ups. Growing warm weather crops in winter, without fossil fuels, in countries outside sub-tropical zones is a goal worth working for.

Winter hoophouse growing

 

Hoophouse Yukina savoy at the end of November.
Photo Ethan Hirsh

Last week I wrote about Winter Preparations for Vegetable Gardens. For those with a hoophouse, here are some notes on all the work we can do to grow winter crops there! For those without a hoophouse as yet, scroll to the end for Twenty Benefits of Having a Hoophouse

First, a roundup of previous blogposts on winter hoophouse topics.

Planning winter hoophouse crops includes a description of how we do our hoophouse crop planning so we can maintain a crop rotation and still pack the beds fully with hardy crops.

Fall hoophouse bed prep and shadecloth removal includes spreading compost, broadforking, and a step-by-step guide to hoophouse fall bed prep.

Hoophouse fall bed prep Plans A-D and spider-webs includes some lovely spider photos and a short video of ballooning, as well as info about our first-planted winter crops.

Hoophouse bed broadforked to loosen up slumped soil. I’m happy to say our soil structure has improved in the 18 years since this photo was taken!
Photo Pam Dawling

Young greens in the hoophouse

After the set-backs with our winter hoophouse greens transplants that I wrote about in Hoophouse fall bed prep Plans A-D and spider-webs, we worked really hard and got the whole house planted up. Most of the transplants have recovered from their transplant shock (wilting each day), during the cloudy weather we had.

The new seedlings are coming up fast and calling on us to thin them. We ended up not needing so many of the Plan D plug flat plants, but we’ve kept them for now “in case” .

Plan D: Winstrip seed flats in our hoophouse on Oct 16, a late attempt to catch up!
Photo Pam Dawling

Ultimately if we don’t need them, they’ll go in a salad mix. I wrote about Making baby salad mix last year. The past two days I have been able to harvest a mix in the hoophouse. The ingredient we are shortest of is lettuce. My first mix was spinach, Bulls Blood beet leaves, a few leaves of Tokyo Bekana, Bright Lights chard, Scarlet Frills, Ruby Streaks and Golden Frills, and a handful of lettuce leaves Red Tinged Winter is growing fastest, of all the varieties we planted this year.

Sowing hoophouse winter crops includes some discussion of the tools we like; pre-sprouting spinach seed and growing multi-leaf lettuce.

What’s growing in the hoophouse; reading; planning for winter is an October view of crops.

Frilly Mustards in our Winter Hoophouse is exactly what it sounds like. Four sowings, six varieties. All delicious.

Making baby salad mix includes a discussion of ingredients and methods, balancing nutrition, color, shape and loft.

Young green Panisse and red Revolution lettuce in our hoophouse in November.
Photo Pam Dawling

Cold-tolerant lettuce and the rest, our January 2018 assessment of the varieties we grew that winter and which survived the unusually cold spell we had. Includes sad photos of the casualties!

Also see my Mother Earth News blogpost from August 2018 Grow Great Lettuce in Winter

———————————————————–

Hoophouse seedlings growing outdoors under insect netting. Starting transplants outdoors helps the rotation by reducing the time the crop is growing in the hoophouse
Photo Pam Dawling

Do you value crop rotation in your hoophouse?

In the winter 2019-2020, a reader in the Pacific Northwest wrote: “This winter I have been re-thinking my crop rotation plan after having some issues (with flea beetle larvae in the soil outsmarting my diligent insect netting of my brassica salad crops). These days I see intensive market gardeners seeming to not worry so much about rotation (i.e. Neversink farm, etc), and yet I’ve always been taught that it is such an important principle to follow. I reviewed your slideshows on crop rotation and also cool crop planning in the greenhouse (which briefly addresses salad brassica rotation with other crops). With how much space I have and the high demand I have for brassicas, for salad mix (mustards) and also the more mainstay cole crops, I had settled on a 2.5 yr between brassica crop rotation (but planting two successions of mustards in the same bed within one year, in the year the bed was in mustards, with a lettuce or other crop breaking up the successions, with the idea that they were very short day and also light feeder crops). Wondering if you think this just doesn’t sound cautious enough, or if this sounds like a reasonable compromise with not having more space to work with (and wanting to satisfy the market demand for brassicas).”

I replied: “Yes, I do think crop rotation is important. I do know some farms seem to have given it up. I think what you are seeing shows one reason why rotation is important. In our hoophouse, we do as you do, allocating brassicas to a space for that winter season and perhaps doing more than one round of brassica crops. Then moving away from brassicas for the next two winters. If doing that doesn’t get rid of the flea beetle problem, and you are being thorough about netting with small-enough mesh netting (sounds like you are, but maybe check the mesh size), then my next step would be spinosad when the flea beetles appear. You can spray the inside of the netting too, and close it quickly. It’s that or a longer rotation, which it sounds like is not financially viable. You could also try farmscaping and/or importing predatory insects (not sure if there are any), Are there beneficial nematodes that attack flea beetle larvae? These are things I don’t know about, but might be worth looking into.”


Doing a spot of research today, I find that Heterorhabditis bacteriaphora, (Hb nematodes) a beneficial nematode fromArbico Organics will attack flea beetles. also known as NemaSeek, and sold separately. This is the wrong time of year for introducing nematodes in most of the US. They need warm weather to thrive.

Another suggestion from Arbico is BotaniGard Maxx & other B. bassiana sprays, which infect and kill adult flea beetles. Repeat applications as needed throughout the growing season.

Kaolin clay (Surround) is another possibility.

Also see Harvest to Table on the topic of dealing with flea beetles

———————————————————–

View through the hoophouse doors in December.
Photo Kathleen Slattery

Add a hoophouse to your food production

For those of you wistfully thinking about a hoophouse, let me help you a step closer to having one next year! Sales of my Year-Round Hoophouse book are doing well, which suggests to me that quite a few gardeners and growers are thinking in this direction.

Twenty Benefits of Having a Hoophouse

  1. An extended growing season because plants are protected from cold weather.
  2. Faster growth and higher total yields.
  3. Beautiful unblemished crops not battered by the elements.
  4. Fewer foliar diseases because the leaves can stay dry.
  5. Crop survival at lower temperatures in the hoophouse than is possible outdoors.
  6. Better crop recovery in winter due to warm sunny days following the cold nights.
  7. Some protection from deer and other pests large and small.
  8. Soil temperature stays above 50F (10C) in zone 6b. Warm soil = faster cold weather growth.
  9. Higher proportion of usable crops – more food, higher sales dollars.
  10. Diverse crop portfolio – grow crops that wouldn’t succeed outdoors in your climate.
  11. Harvest whenever you need the crops, even during pouring rain!
  12. Wonderful working conditions – no need for gloves and hats; take off your coat.
  13. A food garden on a manageable scale.
  14. A place to enjoy practicing intensive food production.
  15. The chance to have an area completely free of weeds – new weed seed doesn’t blow in.
  16. No need to work with heavy machinery.
  17. Much better value for producing crops (per dollar invested) than a heated greenhouse.
  18. Can be constructed by generally-handy people. Specialists are not needed.
  19. NRCS grants are available for some hoophouses. Natural Resources Conservation Service, Environmental Quality Incentives Program, High Tunnel System Initiative.
  20. Ecological energy use. The embodied energy of the plastic is less than the energy that would be used to ship similar produce from somewhere warmer (Eliot Coleman, Four Season Harvest). Another study found this was not true for smaller (9 x 12 m) hoophouses – although the economic incentive for growers is still true, there is no energy efficiency advantage to the planet. Smaller carbon footprint: shipping 1 kg lettuce has 4.3 times the CO2 footprint of locally grown hoophouse lettuce. Plawecki, R., Pirog, R., Montri, A., & Hamm, M. (2014). Comparative carbon footprint assessment of winter lettuce production in two climatic zones for Midwestern market. Renewable Agriculture and Food Systems, 29(4), 310-318. doi:10.1017/S1742170513000161.
September sown White Russian kale (transplanted in October).
Photo Wren Vile

———————————————————–

Know your climate

WeatherSpark climate summary for Louisa, Virginia. Go to the website to click for more information

The WeatherSpark website provides “The Typical Weather Anywhere on Earth”. Enter your nearest town or airport and you get clearly explained info with fascinating graphics of how the weather goes over the year in your locality. Note this is not a forecast site, it’s about average weather for each place. Useful to people who’ve recently moved and want to know what to expect this winter, or to new gardeners who haven’t paid so much attention previously. Or to those who want to check their assumptions (I really thought the wind was out of the west more of the time than records say). There are charts of high and low temperature, temperature by the hour each month, cloud cover, daily chance of precipitation (both rainfall and snowfall), hours of daylight, humidity, wind speed and direction and solar energy. A big help in making wise decisions. I know that climate change is going to cause havoc with averages, and we’ll need to learn to become better weather forecasters individually, and to use soil temperature and other metrics to decide when to plant. This website explains things well.

———————————————————–

Winter gives a time for most of us to ponder success, failure, and possibilities for doing things differently.

 

Cooking Greens in April

Cooking Greens to Harvest in Central Virginia in April

Out with the old! In with the new!

A bed of spring Senposai.
Photo by Wren Vile

Outdoors, collards, kale and spinach that have over-wintered will be coming to an end. Most years, the collards and then the kale bolt in mid-late March, and the overwintered spinach in April.

Fast growing crops like mustard greens and senposai from spring transplanting will be ready to harvest as leaves from early April; collards and kale from mid-April. Beet greens might be ready at the end of April, or it might be May before we get those, depending on the weather and our sowing dates.

From the hoophouse, we are getting the last of most of our indoor greens. The Russian kale, the chard and the Frills (frilly mustards) are bolting. We do have spinach we sowed in January, which will continue all this month. The Bulls Blood beet leaves no longer look very appetizing, but we could cook those up early in the month. The milder winter means earlier bolting this year.

Cooking Greens to Sow in Central Virginia in April

Bright Lights chard in our garden in July.
Photo Pam Dawling

Chard is our best summer cooking green. Chard (Beta vulgaris var. cicla) is the same species as beetroot and, like beets, is a biennial. Hence it will not flower until the second year after planting, and can provide fresh greens all summer and fall, until halted by hard frosts. Even then, the root may survive and regrow the next spring. Leaf beet, also known as perpetual spinach, is a chard, with thinner stems and smaller leaves than most Swiss chard. It is the closest in flavor to spinach for growing in hot weather

Leaf Beet (Perpetual Spinach)
Photo Fedco Seeds

If you prefer spinach in spring, as we do, grow that first, and switch to chard for summer, sowing in plug flats or soil blocks three weeks before your last frost date. (We sow March 24-April 6)

If you want chard in spring, you can start flats earlier or direct seed outdoors two or three weeks before the last frost date.

We also use beet greens for cooking, although our main purpose is to grow beets. Our last date for sowing beets in spring is 4/15.

There are other hot weather greens you could sow in central Virginia and warmer climates.

In the hoophouse, it is definitely too late to plant cooking greens. Anyway, we are filling the tunnel with early tomatoes, squash, cucumbers, and peppers.

Cooking Greens to Transplant in Central Virginia in April

Broccoli head after rain
Photo Wren Vile

Outdoors, we transplant our main cabbage and two sowings of broccoli under nets or rowcover within 6 weeks of sowing. Rowcover is our usual choice, because changeable weather and late frosts are more of an issue here in spring than bugs are. It is important to protect young cabbage and broccoli with 5-8 true leaves from cold stress (<40°F/4.5°C for a few days, or longer at 50°F/10°C). At this stage they are particularly sensitive to cold, which can cause early bolting (and very low yields). After a few weeks, when the weather is more settled, we move the rowcover to newer, more tender crops.

Mid-April: We use saved extra transplants to fill gaps in the broccoli and cabbage plot, at the same time planting out alyssum every 6’ (1.8 m) in the center of the beds. These little flowers attract beneficial insects (see more below).

Ruby Red chard.
Photo Kathryn Simmons

Late in April we will transplant leaf beet and chard – it doesn’t take long for the seedlings to grow. Often we cover the prepared bed with hay mulch, then make two rows of “nests” in the 4’ (1.2 m) wide beds. We don’t space the rows evenly across the bed, but bunch them in close to each other in the middle. This saves the paths for us to walk down.

In the hoophouse, in very early April we use young spinach transplants to fill gaps only in the outer thirds of the beds, leaving the bed centers free for the tomatoes, etc. It would be better to have done this in late February and March, but this year we didn’t get to it. We won’t get high yields, planting this late.

Other Cooking Greens Tasks in Central Virginia in April

Early April: We move rowcover from turnips, senposai, early cabbage, kohlrabi and onions as needed for the broccoli and the maincrop cabbage.

Mid-April: We move rowcover from spring-planted kale, collards, mustard and early lettuce for the tender crops. We finish filling gaps in the broccoli and cabbage plot, at the same time planting out alyssum (sown March 3) one plug every 6’ (1.8 m) in the center of the beds. See the Special Topic for April below, for more on farmscaping, as this method of pest management is called.

Early spring cabbage with alyssum to attract beneficial insects.
Photo Pam Dawling

Late April: We move rowcovers from for the broccoli and the maincrop cabbage. With broccoli, the first weeks after transplanting are vegetative growth, adding leaves until there are about 20, when “cupping” starts — the leaves start to curl up, forming a convex shape rather than growing straight out. The cupping stage is usually10-14 days before harvest starts, depending on temperature. If the weather gets too hot — more than 80°F (27°C) — too soon, the broccoli may grow only leaves, and not head up.

In the greenhouse, we start to have less work, which is fortunate as outdoor work increases.

Special Cooking Greens Topics for April: Farmscaping for Brassicas

Farmscaping is the inclusion of specific flowers to attract beneficial insects. The pollen and nectar offer an alternative food source to beneficial insects when their insect prey is scarce. And if their insect prey is right by the flowers, what could be better?

Alyssum.
Photo Raddysh Acorn

We plant Sweet Alyssum in our spring broccoli patch to attract predators of aphids and caterpillars; Putting 5 percent of the crop area in plants that attract beneficial insects can seriously reduce pest numbers. Sweet alyssum, yarrow, dill, coriander (cilantro), buckwheat, mung beans, other peas and beans, black oil-seed sunflower, calendula and cleome all work well to attract a range of insects (especially ladybugs and lacewings) that eat or parasitize aphids. Pans of water and gravel will help attract aphid midges and lacewings. The gravel provides surfaces for the insects to land on while drinking. Farmscaping can make other insect control unnecessary in a good year. Beneficials will generally move up to 250 feet (75 m) into adjacent crops.

We also plant “insectaries” around the garden, usually at the ends of beds with crops that will be growing for several months. These flowers are planted inside rings sawn from a plastic bucket. The rings alert the crew that something special is there, not just a clump of weeds. Mix flowers to have something blooming all the time.

Insectary circle with sunflower, tithonia, borage, zinnia.
Photo Pam Dawling

Another method for incorporating farmscaping is to plant beneficial-attracting perennial flowers in areas that are too challenging to use for production: edges, slopes, tight corners, hedgerows, and field borders.

Other Pest Management for Brassicas

Using rowcovers keeps many pests off the plants while they are small. We have not had much trouble with aphids, perhaps partly because our overhead sprinklers wash them off and they can’t travel far. Insecticidal soap sprayed three times, once every five days, can usually deal with aphids. Our worst pest is the harlequin bug. For lack of a better organic solution, we handpick them. Ladybugs are reputed to eat harlequin bug eggs.

Sometimes we have had enough cabbage worms to make Bt (Bacillus thuringiensis) necessary, but usually paper wasps eat the caterpillars. The action level threshold is an average of 1 cabbage looper, 1.5 imported cabbageworms, 3.3 armyworms or 5 diamondback moth larvae per 10 plants. Below this level you can do watchful waiting rather than spraying with Bt or spinosad. We are lucky enough to have the naturally occurring wasp parasite of cabbage worms, the Braconid wasp Cotesia species, which are found as small cottony white or yellowish oval cocoons in groups on brassica leaves. The Cotesia wasps like umbelliferous flowers, and overwinter on yarrow as well as brassicas. If you find Cotesia cocoons in the fall and your brassicas aren’t diseased, you can leave plants in the field over winter. Or you could collect up leaves with cocoons in late fall and store them at 32°F–34°F (0°C–1°C) until spring. Hopefully no one will clean out your fridge without checking.

Richard McDonald has good information in his Introduction to Organic Brassica Production. He reports that broccoli plants with six to sixteen leaves (just before cupping) can lose up to 50 percent of their leaf area without reducing yield. Moderate defoliation (20–30 percent) causes the plant to exude chemicals that attract parasitic wasps and predatory insects. If you relax and allow this amount of defoliation early on, you can encourage these beneficial insects to move in and begin foraging in the area. Once the plants cup, you want to prevent further defoliation by having the most beneficials and the fewest pests on site. If pest levels are above the action threshold, cupping is the stage to take action, and probably not earlier.

Broccoli side shoots offer harvest after the main head is cut.
Photo Nina Gentle

To float out worms and aphids after harvest (before cooking!), use warm water with a little vinegar and soak for up to fifteen minutes, then rinse.

Winter-Kill Temperatures of Cold-Hardy Vegetables 2020

Overwintered Vates kale in central Virginia in March.
Photo Nina Gentle

At the Organic Association of Kentucky Conference, I gave a a presentation on Winter High Tunnel and Outdoor Vegetable Production. You can see it here. Click on the diagonal arrow icon to see it full screen, then click on the right pointing triangular arrow

Winter-Kill Temperatures of Cold-Hardy Vegetables 2020

I keep records of how well our crops do in the colder season, both outdoors and in our double-layer hoophouse. I note each increasingly cold minimum temperature and when the various crops die of cold, to fine-tune our planning for next year. We are in zone 7a, with an average annual minimum temperature of 0-5°F (-18°C to -15°C). 

The winter 2019-2020 has been mild, with our lowest temperature being a single night at 12°F (-11°C). The Koji became completely unmarketable but did not completely die. Yukina Savoy is indeed hardier, being OK down to 10°F (-12°C). We had one night at 13°F (-10°C) and two each at 17°F (-8°C), 18°F (-8°C also) and 19°F (-7°C).

This winter I noted the death of rhubarb stems and leaves at 25°F (-4°C), rather than 22°F (-6°C), as I noted a year or two ago.

In early January 2018, we had some extremely cold temperatures of -8°F and -9°F (-22°C and -23°C). The winter of 2018-2019 was not as brutal. Our lowest temperatures were 6°F (-14°C) in late January, 8°F (-13°C) in December 2018 and a couple of 11°F (-12°C). I found that senposai is more cold-tolerant than I had thought. Averaging our winter low over those three winters gives 3.2°F (-16°C), completely within the zone 7a range.

My other results from other years still hold up.

I also learned that there is more damage when the weather switches suddenly from warm to cold. And that the weatherman in Raleigh, NC says it needs 3 hours at the critical temperature to do damage.

Radicchio seeds from Seeds from Italy

Notes on Chicories and Endives

We gave up growing chicories and endives because we really didn’t like the bitterness. I decided to do some more online research to make sure I wasn’t spreading untruths. Chicories and endives fall into two groups, but they are confusing because the common names sometimes suggest the opposite group than they are botanically. Here’s the best info I have. If you know differently, please leave a comment.

Cichorium intybus, commonly called chicories, are mostly heading crops. The group includes radicchio, both Treviso and Chioggia (hardy to about 20°F (-7°C). Belgian Witloof endive (the kind for forcing chicons) is also a chicory. It dies at 25°F (-4°C). Sugarloaf chicory is the least hardy chicory, and dies at 27°F (-3°C).

Cichorium endivia, commonly called endives, are mostly loose-leaf crops, less cold-hardy than intybus types (chicories). This group includes Frisée types and escaroles, which are also known as Batavian endives. They generally survive down to 22°F (-6°C), although Perfect and President endives can survive down to 10°F (-12°C) – can anyone confirm or deny this?

Using the List

Unless otherwise stated, these are killing temperatures of crops outdoors without any rowcover. All greens do a lot better with protection against cold drying winds. Note that repeated cold temperatures can kill crops that can survive a single dip to a low temperature, and that cold winds, or cold wet weather can destroy plants quicker than simple cold. Your own experience with your soils, microclimates and rain levels may lead you to use different temperatures in your crop planning.

Hoophouse beds in November.
Photo Ethan Hirsh

Hoophouse Notes

Our double-plastic hoophouse keeps night time temperatures about 8F (4.5C) degrees warmer than outdoors, sometimes 10F (5.5C) degrees warmer. Plus, plants tolerate lower temperatures inside a hoophouse. The soil stays warmer; the plants recover in the warmer daytime conditions (it seems to be the night+day average temperature that counts);

In the hoophouse (8F (4.5C) degrees warmer than outside) plants without extra rowcover can survive 14F (7.7C) degrees colder than they could survive outside; with thick rowcover (1.25oz Typar/Xavan) at least 21F (11.6C) degrees colder than outside.

For example, salad greens in our hoophouse can survive nights with outdoor lows of 14°F (-10°C). Russian kales, lettuce, mizuna, senposai, spinach, tatsoi, turnips, Yukina Savoy survived a hoophouse temperature of 10.4°F (-12°C) without rowcover, -2.2°F (-19°C) with. Bright Lights chard got frozen leaf stems.

Young Bright Lights chard.
Photo Pam Dawling

Lettuce varieties for a solar-heated winter greenhouse or hoophouse in zone 7a: (hardiest are in bold) Buckley, Ezrilla, Green Forest, Green Star, Hampton, Hyper Red Rumpled Wave, Marvel of Four Seasons, Merlot, New Red Fire, North Pole bibb, Oscarde, Outredgeous, Pirat, Red Cross bibb, Red Sails, Red Salad Bowl, Red Tinged Winter, Revolution, Rouge d’Hiver, Salad Bowl, Sylvesta bibb, Tango, Winter Marvel, Winter Wonderland.

Outdoor killing temperatures of crops (unprotected unless stated)

35°F (2°C):  Basil.

32°F (0°C):  Bush beans, some cauliflower curds, corn, cowpeas, cucumbers, eggplant, limas, melons, okra, some pak choy, peanuts, peppers, potato vines, squash vines, sweet potato vines, tomatoes.

27°F (-3°C): Many cabbage varieties, Sugarloaf chicory (takes only light frosts).

25°F (-4°C): Some cabbage, chervil, Belgian Witloof chicory roots for chicons, and hearts, Chinese Napa cabbage (Blues), dill (Fernleaf), some fava beans (Windsor), annual fennel, some mustards (Red Giant, Southern Curled) and Asian greens (Maruba Santoh, mizuna, most pak choy, Tokyo Bekana), onion scallions (some are much more hardy), radicchio, rhubarb stems and leaves.

Tokyo bekana in our hoophouse.
Photo Twin Oaks Community

22°F (-6°C): Some arugula (some varieties are hardier), Bright Lights chard, endive (Escarole may be a little more frost-hardy than Frisée), large leaves of lettuce (protected hearts and small plants will survive colder temperatures).

20°F (-7°C): Some beets (Bulls Blood, Chioggia,), broccoli heads (maybe OK to 15°F (-9.5°C)), Brussels sprouts, some cabbages (the insides may still be good even if the outer leaves are damaged), some cauliflower varieties, celeriac, celtuce (stem lettuce), some head lettuce, some mustards/Asian greens (Tendergreen, Tyfon Holland greens), flat leaf parsley, radicchio, both Treviso and Chioggia, radishes (Cherry Belle), most turnips (Noir d’Hiver is the most cold-tolerant variety).

Large oat plants will get serious cold damage. Oats seedlings die at 17°F (-8°C)

Canadian (spring) field peas are hardy to 10-20°F (-12 to -7°C).

15°F (-9.5°C): Some beets (Albina Verduna, Lutz Winterkeeper), beet leaves, some broccoli, some cabbage (Kaitlin, Tribute), covered celery (Ventura), red chard, cilantro, fava beans (Aquadulce Claudia), Red Russian and White Russian kales, kohlrabi, some lettuce, especially medium-sized plants with 4-10 leaves (Marvel of Four Seasons, Olga, Rouge d’hiver, Tango, Winter Density), curly leaf parsley, rutabagas (American Purple Top Yellow, Laurentian), broad leaf sorrel, most covered turnips, winter cress.

Young Cylindra beets.
Photo Wren VIle

12°F (-11°C): Some beets (Cylindra,), some broccoli perhaps, Brussels sprouts, some cabbage (January King, Savoy types), carrots (Danvers, Oxheart), most collards, some fava beans (mostly cover crop varieties), garlic tops if fairly large, Koji greens, most fall or summer varieties of leeks (Lincoln, King Richard), large tops of potato onions, covered rutabagas, some turnips (Purple Top).

10°F (-12°C): Covered beets, Purple Sprouting broccoli for spring harvest, a few cabbages (Deadon), chard (green chard is hardier than multi-colored types), some collards (Morris Heading can survive at least one night at 10F), Belle Isle upland cress, some endive (Perfect, President), young Bronze fennel, Blue Ridge kale, probably Komatsuna, some leeks (American Flag, Jaune du Poiteau), some covered lettuce (Pirat, Red Salad Bowl, Salad Bowl, Sylvesta, Winter Marvel), covered winter radish (Daikon, China Rose, Shunkyo Semi-Long survive 10°F/-12°C), Senposai leaves (the core of the plant may survive 8°F/-13°C), large leaves of savoyed spinach (more hardy than smooth-leafed varieties), Tatsoi, Yukina Savoy.

Oats cover crop of a medium size die around 10°F (-12°C). Large oat plants will die completely at 6°F (-17°C) or even milder than that.

5°F (-15°C): Garlic tops even if small, some kale (Winterbor, Westland Winter), some leeks (Bulgarian Giant, Laura), some bulb onions, potato onions and other multiplier onions, smaller leaves of savoy spinach and broad leaf sorrel. Many of the Even’ Star Ice Bred greens varieties are hardy down to 6°F (-14°C), a few unprotected lettuces if small (Winter Marvel, Tango, North Pole, Green Forest).

Garlic shoots in January.
Photo Pam Dawling

0°F (-18°C): Chives, some collards (Blue Max, Winner), corn salad (mâche), garlic, horseradish, Jerusalem artichokes, Even’ Star Ice-Bred Smooth Leaf kale, a few leeks (Alaska, Durabel, Tadorna); some bulb onions, yellow potato onions, some onion scallions, (Evergreen Winter Hardy White, White Lisbon), parsnips (probably even colder), salad burnet, salsify (?), some spinach (Bloomsdale Savoy, Olympia). Walla Walla onions sown in late summer are said to be hardy down to -10°F (-23°C), but I don’t trust below 0°F (-18°C)

Crimson clover is hardy down to 0°F (-18°C) or slightly colder

 -5°F (-19°C): Leaves of overwintering varieties of cauliflower, Vates kale survives although some leaves may be too damaged to use.

-10°F (-23°C) Austrian Winter Field Peas and Crimson clover (used as cover crops).

-15°F (-26°C) Hairy vetch cover crop – some say down to -30°F (-34°C)

-20°F (-29°C) Dutch White clover cover crops – or even -30°F (-34°C)

 -30°F to -40°F (-34°C to -40°C): Narrow leaf sorrel, Claytonia and some cabbage are said to be hardy in zone 3. I have no personal experience of this.

 -40°F (-40°C) Winter wheat and winter rye (cover crops).

Cooking Greens in March

 

White Russian kale in our hoophouse in March.
Photo Pam Dawling

Cooking Greens to Harvest in Central Virginia in March

Eat Your Greens! More Bolting Greens in the Hoophouse, Sigh.

Outdoors, we can still harvest collards, kale and spinach. We also have very nice spinach in our coldframes, where the crop gets better protection from the cold than the outdoor beds.

From the hoophouse, in the cooking greens department, we still have plenty of Bulls Blood beets (the leaves are getting a bit big and leathery for salads), chard, frills (frilly mustards such as Ruby Streaks, Golden Frills, Scarlet Frills), White and Red Russian kales, and spinach.

In the hoophouse, the extra warmth (at last!) and the considerably lengthening days are causing lots of the greens to bolt. This year our turnips, tatsoi, senposai, and the Koji were all bolting before the end of February, although other years these have not bolted until mid-March (or the later sowings at least). We are harvesting lots of greens, trying to eat them all before we lose them!

We are keeping an eye on our Russian kales, chard, beet greens and later spinach sowings. They usually last till late April or even early May, but this milder winter may mean they will bolt earlier this year.

Cooking Greens to Sow in Central Virginia in March

Outdoors in early March, or preferably mid-February we direct sow spinach if our January transplant sowings failed. This year, we have plenty of transplants. In early March we sow turnips, and give them rowcover.

In the greenhouse in early March, we sow broccoli #3, in open 3” (7.5 cm) flats. This sowing is intended as a gap-filler for the first two sowings, if any plants die after transplanting, or if we don’t get enough plants from the first two sowings.

Winstrip tray with chard seeds.
Photo Pam Dawling

In late March, we sow sow chard and leaf beet. Leaf beet, also known as perpetual spinach, is a chard, with thinner stems and smaller leaves than most Swiss chard. It is the closest in flavor to spinach for growing in hot weather that I have found. Because it is a biennial, it will not bolt the first year.

In the hoophouse, we do not usually sow any cooking greens. Because the hoophouse is much warmer on sunny days, annual greens (all the brassicas) will quickly bolt. We do better to focus on outdoor planting.

Cooking Greens to Transplant in Central Virginia in March

Outdoors, we transplant cabbage #1 from flats in early March (3/10). These are fast-growing early varieties such as the hybrid Farao (65 days) and the OP Early Jersey Wakefield (63 days). This year we are also trying the larger but slower Early Flat Dutch (85 days)

A bed of Early Jersey Wakefield cabbage in mid-May.
Photo Pam Dawling

In mid-March, we transplant collards, mustard, kale (last date 4/1), and senposai. We use rowcover over all our early transplants outdoors, for a few weeks until the weather is milder. By then, we usually need the rowcover somewhere else for new transplants or sowings.

It is important to protect young cabbage and broccoli with 5-8 true leaves from cold stress (<40°F/4.5°C for a few days, or longer at 50°F/10°C). At this stage they are particularly sensitive to cold, which can cause early bolting (and very low yields).

In the hoophouse, after February 20 we use young spinach transplants to fill gaps only in the outer thirds of the beds, leaving the bed centers free for tomatoes, etc. in mid-March.

Other Cooking Greens Tasks in Central Virginia in March

Open flat of broccoli seedlings.
Photo Wren Vile

In the greenhouse, we are busy spotting (see February Special Topic) all our plants to give them two weeks of greenhouse protection and 10-14 days in the coldframe before their transplant date. During early to mid-March, this means the senposai, mustard, broccoli and main crop cabbage, as well as collards and kale (if we don’t have enough of those for bare-root transplanting from the hoophouse).

Special Cooking Greens Topics for March: Trap Flea Beetles, Extra Month of Greens in the Hoophouse

A row of mustard greens can be used to lure flea beetles.

They like the pungent compounds in brassicas.  Once you have lured the flea beetles you need to deal with them before you create a flea beetle breeding ground. Flaming the mustard plants is one possibility. If you have poultry that likes eating flea beetles, you could cut off some of the leaves and carry them to the chicken run. Bug vacuums are also a possibility. Another approach is to hold an inverted bucket lined with sticky trap compound over the plants and rap the stems with a stick. If you’re lucky, the pests will stick in the bucket.

North edge bed in our hoophouse flagged up for digging holes to plant peppers.
Photo Pam Dawling

Hoophouse transition to give an extra month of greens.

Preparing our hoophouse beds for our early tomatoes, peppers, cucumbers and squash is very different from our fall bed prep for winter greens. We stretch a long tape measure down the center of each bed, and put a flag every 2 ft (60 cm). All our transplanted crops in spring are at this spacing. We then prioritize harvesting the greens which are close to the flags. A day or two before transplant day, we dig a hole at each flagged spot and add a shovelful of compost to each hole. After transplanting the new crop plants, and watering them in, we start harvesting the greens directly to the south (in front of) the new plants. As the plants get larger, we pull more of the greens between the transplants. Anything that is touching leaves is too close and has to go. After a few weeks we also need to harvest the last of the greens, to the north of the transplants, which by then have reached a good size. This method gives us an extra month of greens and initially the relatively large greens protect the small transplants from too much direct sun or from cold breezes. If the night will be frosty, we pull rowcover over the beds – the greens hold the rowcover off the tender plants.

Tomato plants in our hoophouse, in early April, planted among the winter greens
Photo Kathryn Simmons

Cooking Greens in February

Plentiful spinach in our cold frame in winter.
Photo Wren Vile

Cooking Greens to Harvest in Central Virginia in February

Harvest in Time! Lots of Bolting Greens in the Hoophouse!

Outdoors, we can still harvest collards, kale and spinach. This winter our chard has died. Remember that red chard is hardier than multi-colored and green chard is hardier still. To maximize your chance of keeping chard alive over the winter, use hoops and rowcovers (in zone 6-8) or, in colder zones, cut the tops off the plants (above the growing point) before it gets much below 15F (-9C), remove those leaves, then cover the bed with a mulch of thick straw, hay or tree leaves. Mulching doesn’t work in milder climates, especially those with back-and-forth temperatures) because new growth forces up out of the mulch and gets killed.

From the hoophouse we continue harvesting chard, Frills, kale, senposai, spinach, tat soi, turnip greens, and also yukina savoy (if we had it). We normally grow the Frills as salad crops, but once they get large and plentiful, we can cook some.

Bolting Golden Frills and Scarlet Frills.
Photo Pam Dawling

In the hoophouse, the extra warmth (sometimes!) combined with the reliably lengthening days causes some of the greens to start bolting. In January, I told you the order of bolting of our hoophouse greens. Our Koji has all bolted by February 1, and I pine for Yukina Savoy which usually lasts till early-mid March here, from our second winter sowing. We didn’t have any this winter.

We are keeping an eye on our turnip greens #1 (they will bolt in mid-February); tatsoi #2, spinach #1, and turnip greens #2 (usually bolt in early March). Our senposai and our turnips #3 usually don’t bolt till mid-March. Our Russian kales, chard, beet greens and January spinach sowings last till late April or even early May.

Hoophouse turnips have delicious greens too!
Photo Wren Vile

Cooking Greens to Sow in Central Virginia in February

Outdoors in mid-February, we sow spinach if our January transplant sowings failed. We presprout 4oz/bed spinach for 1 week before sowing. This rarely needs to happen, as we have a backup transplant sowing date to seed in flats in the greenhouse, if our first-line hoophouse sowing of transplants doesn’t come up well. This year, those look great!

In the greenhouse in early February, we sow: kale, cabbage, mustard, collards, senposai, broccoli #1, kohlrabi in open 3” (7.5 cm) flats.

In late February, we sow broccoli #2. This year we have reduced the size of our planting to make it more manageable.

In the hoophouse, December 15-February 15 is the slowest growing time. We do sow some salad crops, but not usually any cooking greens. if the January hoophouse sowings of kale and collards have come up well, we don’t need to sow those in the greenhouse this year.

We have a couple of unexpected gaps this year. We followed Radish #2.5 (an extra sowing we squeezed in on October 20) with Frills (frilly mustards) and we plan to follow some of our Koji #2 with a quick catch crop of Tokyo Bekana, marking five rows in the bed, but leaving the central row unsown. This will hopefully let us leave the greens growing after we transplant the warm weather crops down the centerline of the bed.

Young Ruby Streaks, Golden Frills and Scarlet Frills provide continuous harvest after the older ones bolt.
Photo Pam Dawling

Cooking Greens to Transplant in Central Virginia in February

Outdoors, we transplant spinach from hoophouse [or flats] in early February

In the hoophouse, from January 25 to February 20 we fill gaps that occur in the beds with spinach wherever the gaps are, using the spinach Filler Greens which were sown October 24 and November 9 (spinach). We’re careful not to fill any places that will be sown in new crops in February, such as where we sow a row of early snap peas, or the salad crops I mentioned earlier.

From February 20, we only transplant spinach to fill gaps on the outer thirds of the beds, leaving the bed centers free for tomatoes, etc. in mid-March.

Other Cooking Greens Tasks in Central Virginia in February

Flats of cabbage in our greenhouse in February.
Photo Pam Dawling

In early February in the greenhouse we spot cabbage and kale. In late February, we spot senposai, cabbage #2 and collards. See the Special Topic below for more about the task we call ”spotting”. Other names for this task include “bumping up”and “pricking out.”

We really try to finish transplanting spinach outdoors, as our springs are short and quickly heat up, taking the spinach plants with them.

We weed our over-wintered spinach, kale and collards. Hoeing isn’t so effective in early spring, as the chickweed, henbit and dead nettle too readily re-root on damp soil. Hand-pulling weeds is slow, but more effective. Another approach is to hoe several times, choosing dry breezy sunny days.

During January we had two nights at 13F (-10.5C) and 12F (-11C). The Koji are looking quite damaged, beyond marketable but not beyond salvageable for home use. We grew too much of this, so we still have plenty to eat! The outdoor senposai is also damaged, but as this is a loose-leaf crop it could recover if it doesn’t get colder.

As I reported in January, we didn’t cover the spinach this winter, because of issues with rowcover fibers getting in the food. The plants are looking quite small, while those in the coldframes (with rowcover) are growing well. I have been expecting the growth of the uncovered spinach to be a lot slower, as spinach (like kale and lettuce) makes some growth whenever the temperature is 40°F (4.5°C) or more. 10°F (-12°C) could kill the large leaves and 5°F (-15°C) can kill spinach entirely. So far, temperatures haven’t get that cold this winter.

Weeding rowcovered spinach in winter. This winter we tried not using rowcover.
Photo Wren Vile

Special Cooking Greens Topic for February:

Planning our Field Planting Schedule.

In January we prepare our new Seedlings Schedule, then our complex Fall Brassica Spreadsheet and Map, Field Planting Schedule, Hoophouse Schedule for March to September crops (those are not cooking greens!), and then our Raised Bed Plan and our monthly Garden Calendar.

Field Planting Schedule:

We allow 6 hours. We bring the previous year’s greenhouse copy of the Seedlings Schedule, the shed copies (the copies we wrote notes on) of the previous year’s Field Planting Schedule and the shed and seed bucket copies of the Lettuce Log. We also bring the new (current year’s) Fall Brassica Schedule, Seedlings Schedule, Seed Order, Garden Plan, Rotation Plan, Maps, Succession Crop Plan, Sweet Corn Plan, Brassica Plan and Tomato Plan and any notes we made while doing the year’s planning so far.

  1. We work in Excel, copying last year’s Schedule to a new Worksheet and modifying that.
  2. We highlight and clear the contents of the“Location” column (Crop rotation in action!)
  3. We check against last year’s Shed copy and Field Manual copy of the Field Schedule. As we go, we make a list of questions or points to fix later.
  4. We check against the Seedlings Schedule for last year and the current year, for transplant date and varieties, row feet of the transplanted crops. (Leave the direct seeded crops varieties and row feet for step 6).
  5. Next we highlight the data, sort alphabetically by Vegetable, Variety to make the next stages easier.
  6. We check against the Seed Order (and Succession Plan as needed) for varieties and row feet of direct seeded crops.
  7. We check against the Tomato Plan for main crop and late bed.
  8. We check against the Garden Rotation Plan, Maps and Succession Crop Plan.
  9. We fill gaps in the Location column, in In-row Spacing and Space Between Rows cols.
  10. We check against Fall Brassica Schedule from the current or previous year, revising sowing dates, row feet, transplanting dates.
  11. We check against the Lettuce Log.
  12. We check against Hoophouse Schedule, for transplants in and out.
  13. We clean up the Notes column keeping useful info, adding any new useful info, checking against running list of things to fix.
  14. With all that done, we sort by Transplant date; then by Vegetable, then by Variety.
  15. We tidy up the page layout and print a draft copy
  16. We proofread and fix anything that didn’t make sense.

 

Hoophouse Musings, Bugs, Okra, Edible Landscaping Workshops in Maryland

Hoophouse beds in December. This is why we have a hoophouse!
Photo Wren Vile

Winter hoophouse posts in Mother Earth News newsletter

Sowing and Transplanting Winter Crops in a Hoophouse

Grow Great Lettuce in Winter

Winter hoophouse lettuce
Photo Kathryn Simmons

———————————————————

A photo of a Tiny House from Wikipedia

Would you live in a hoophouse?

A reader wrote in:

“I have actually been thinking of building a tiny house and putting it inside a big hoophouse, creating a living area that would include a yard, trees, and gardens – allowing me to snowbird in place in northern New England – but I’m concerned about outgassing, since I’d be there almost 24-7 most days (I work out of my home). Have you done any research on outgassing of hoophouses?”

A Tiny House is generally a residential structure under 400 sq. ft

First off, No I haven’t done any research about hoophouse off-gassing, but I wouldn’t worry about out-gassing from the polyethylene of the hoophouse. Other products  are much closer to your nose: All the materials used to construct, preserve and decorate the house and all the products within the house, such as furniture,  fabrics, soaps, appliances etc.

There are some other things I’d wonder about:

1.      Temperature. When the sun shines, the interior of the hoophouse warms up. When the sun doesn’t shine, it doesn’t. Would you heat the tiny house? You’d have to avoid heating systems that could damage the plants.

2.      Snowfall. When it snows, you need to remove the snow from the roof of the hoophouse. Some snow can be carefully pulled down from the outside. Usually we also walk around inside the hoophouse bouncing a broom on the inside of the plastic to move the snow off. You can’t do that if you have a house in the way.

3.      Humidity. In the winter we grow cold-tolerant hoophouse crops. We are aiming for 65 F (18C). We need fresh air for the plants and to deter fungal diseases. It doesn’t work to keep the hoophouse sealed up and “cozy”!

4.      Strong winds. In hurricanes and gales, hoophouses sometimes collapse or get destroyed. You don’t want to be inside when that happens.

5.      Height. Our hoophouse is less than 14 ft (4 m) at the apex.

In conclusion I’d say it’s better to have a small patio seating area within your hoophouse for suitable sunny days, rather than plan to live inside all the time.
Brassicas in a nematode-fighting hoophouse crop rotation in Hawaii.
Credit Gerry Ross, Kupa’a Farms

Do you value crop rotation in your hoophouse?

A reader in the Pacific Northwest wrote: “This winter I have been re-thinking my crop rotation plan after having some issues (with flea beetle larvae in the soil outsmarting my diligent insect netting of my brassica salad crops). These days I see intensive market gardeners seeming to not worry so much about rotation (i.e. Neversink farm, etc), and yet I’ve always been taught that it is such an important principle to follow. I reviewed your slideshows on crop rotation and also cool crop planning in the greenhouse (which briefly addresses salad brassica rotation with other crops). With how much space I have and the high demand I have for brassicas, for salad mix (mustards) and also the more mainstay cole crops, I had settled on a 2.5 yr between brassica crop rotation (but planting two successions of mustards in the same bed within one year, in the year the bed was in mustards, with a lettuce or other crop breaking up the successions, with the idea that they were very short day and also light feeder crops). Wondering if you think this just doesn’t sound cautious enough, or if this sounds like a reasonable compromise with not having more space to work with (and wanting to satisfy the market demand for brassicas).”

I replied: “Yes, I do think crop rotation is important. I do know some farms seem to have given it up. I think what you are seeing shows one reason why rotation is important. In our hoophouse, we do as you do, allocating brassicas to a space for that winter season and perhaps doing more than one round of brassica crops. Then moving away from brassicas for the next two winters. If doing that doesn’t get rid of the flea beetle problem, and you are being thorough about netting with small-enough mesh netting (sounds like you are, but maybe check the mesh size), then my next step would be spinosad when the flea beetles appear. You can spray the inside of the netting too, and close it quickly. It’s that or a longer rotation, which it sounds like is not financially viable. You could also try farmscaping and/or importing predatory insects (not sure if there are any), Are there beneficial nematodes that attack flea beetle larvae? These are things I don’t know about, but might be worth looking into.”

 

Late sweet corn and sweet potatoes
Credit Ezra Freeman

Sweet Potato fends off bugs

Modern Farmer has this fascinating article about sweet potato plants alerting their neighbors to pest attacks.

Researchers from the Max Planck Institute and the National Taiwan University found that when sweet potato plants are attacked by insects, they emit a bouquet of odors and start production of a protein called sporamin that makes them unappetizing. Neighboring sweet potatoes sense the odors and start their own production of sporamin.


 

A new Tokyo bekana transplant attacked by vegetable weevil larvae October 10
Photo Pam Dawling

Insect damage cause stress-response production of anti-oxidants

In a related piece of news, Agrilife Today from Texas A&M AgriLife Research has found some evidence that wounded plants produce anti-oxidants as a stress response, which may make them healthier for human consumption. Read the report here.

Edible Landscaping with a Permaculture Twist Spring Series

Michael Judd in cooperation with Common Market CO+OP is presenting a combination of hands-on workshops at Long Creek Homestead and evening talks at the Common Market, Frederick Maryland.

Click here for info on Spring Workshops/Talks/Tours

·        Inoculating Mushrooms

·        Fruit Tree Grafting

·        Herb Spirals

·        Creating Growing Beds- Swales and Hugelkultur

·        Edible Landscaping & Straw Bale Home Tour

·  For the Love of PawPaws


 

Fire Ants have reached Toronto

A reader wrote in that the European Fire Ant is now found in Toronto.


“There were two nests of these in my allotment garden 2018.
They actually moved the nest in order to be closer to the zucchini
plants.  Hand on heart: I never had  any cucumber beetles develop past
the instar stage.  The ants did not eat the eggs but they ate the larvae
as soon as they hatched.  Same for potato beetle.  My neighbours had
the best cucumber harvest in history. 
What I’ve read is these Fire Ants kill colonies of native ants.  Summer 2019 I had a Pavement Ant war that went on for days.  Clearly the Fire Ants did not wipe them out.  There are black ants and other smaller red ants
in my garden.  The Fire Ants appear to have moved on for some reason known
only to themselves.   Perhaps they too have enemies.”
“There’s a guy with a Youtube channel who keeps ant colonies.   AntsCanada although he is in the Philippines.  What happened was the feral Pharaoh Ants invaded his colony of Fire ants and killed them.  Pharaoh Ants are much smaller but perhaps that’s what gave them the advantage.   We have Pharaoh ants in Toronto also.   I spend a lot of my time looking at the little critters in my garden.  Like red velvet mites:  there were many in 2016.  Have not seen a single one in two years now. “

Video of Okra Taste Testing

Chris Smith, author of The Whole Okra

Chris Smith, author of  The Whole Okra: Chris has a video of
the taste testing on  Youtube, https://www.youtube.com/watch?v=sAy0pouxlME

Cooking Greens in January

Morris Heading collards, a reliable winter crop. Photo Kathryn Simmons

Cooking Greens to Harvest in Central Virginia in January

Harvest in time! Freezing or Bolting Greens!

Outdoors, the temperatures continue to get colder in January. In our garden outdoors, there are collards, kale, spinach, and sometimes chard,  senposai, and Yukina savoy, and over-wintered cabbage (not for much longer!).

Hopefully there is also cabbage stored in the cooler. The most cold-hardy greens are what we depend on for the next two months.

Tatsoi in our hoophouse in December.
Photo Kathleen Slattery

From the hoophouse we continue harvesting chard, Chinese cabbage, kale, frilly mustards, pak choy, senposai, spinach, (including thinnings from the newer sowings),   tatsoi (thinnings from the newer sowings, whole plants from the September 7 sowing), Tokyo bekana/Maruba santoh plants, turnip greens, yukina savoy.

In the hoophouse, the extra warmth combined with the lengthening days causes some of the brassicas to start bolting. After the Winter Solstice the order of bolting of our hoophouse greens is: tatsoi #1 (meaning, our first sowing 9/6), Tokyo bekana, Maruba santoh (all in early January); pak choy, Chinese cabbage, Yukina Savoy #1 (late January); turnip greens #1 (mid-February); Komatsuna, Yukina Savoy #2, tatsoi #2, spinach #1, turnip greens #2 (early March); Senposai, turnips #3, (mid-March); Russian kales (early April); chard, beet greens, later spinach sowings (late April or even early May.)

Tokyo bekana in our hoophouse in late December.
Photo Pam Dawling

Our knowledge of what will bolt first informs our plan of where to put the new crops we want to plant. To make space to sow spinach on 1/16, we need to clear the Tokyo bekana (and Maruba santoh) and the first tatsoi by 1/14. We keep a close eye on the Chinese cabbage and pak choy. Normally these will bolt in January, and we harvest the whole plants this month. They will be followed by sowings of kale and collard starts for outdoors on 1/24.

Chinese cabbage in November, not yet fully headed.
Photo Ethan Hirsh

It might seem sad, at first glance, that these big greens will bolt this month if we don’t harvest them in time, but in fact, it all works out rather well. The rate of growth of the “cut-and-come-again” leaf greens slows down in December and January, and while we eat the big heads of Tokyo bekana, Maruba santoh, Chinese cabbage, pak choy and the not-tiny tatsoi, we ignore the leaf greens, giving them more time to grow.

Pak Choy in our hoophouse in late December.
Photo Pam Dawling

December 15-February 15 is the slowest growing time for our hoophouse crops.

When the daylight is shorter than 10 hours a day, not much growth happens. The dates depend on your latitude. In Central Virginia, at latitude 38° North, this Persephone period (named by Eliot Coleman) lasts two months, from November 21 to January 21. We have found in practice, that soil temperature also affects the growth rate. And so we have a three week lag in early winter before the soil cools enough to slow growth, and then another 3 week lag  in January before it warms up enough again.

Transplanting spinach from a Speedling flat.
Photo Denny Ray McElya

Cooking Greens to Sow in Central Virginia in January

Outdoors, we sow nothing.

In the greenhouse we tidy up the workspace, “fire up” the germinator fridges (germination chambers made from the carcasses of dead fridges), and prepare our new Seedlings Schedule (see Special Topic for January below)

Around 1/17 we sow some fast early cabbage, such as the OP Early Jersey Wakefield and the hybrid Farao. (We sow lettuce and scallions then too, to keep them company.) At the end of January we sow spinach in Speedling flats if our hoophouse sowings have been insufficient. We have trialed the bare-root spinach against the Speedling spinach and both do equally well.

In the hoophouse, in mid-January we sow Spinach #4, to transplant in gaps in the hoophouse. We usually clear Tatsoi #1 to make space for this. Of the varieties we tried, Reflect does best for this planting, followed by Acadia and Escalade. This winter we have had difficulty buying Acadia and Escalade and are going to try Abundant Bloomsdale alongside Reflect.

Spinach seedlings in our hoophouse for bare-root transplanting.
Photo Pam Dawling

We also sow Spinach #5 for bare-root transplanting outdoors in February or early March under rowcover. This follows the Tokyo bekana or Maruba Santoh as noted above. Reflect and Acadia do well for this purpose, with Escalade close behind. We’ll have to improvise this spring.

In late January (1/24, 1/25), we sow kale and collards for transplanting outdoors in March. I have written before about how well these bare-root transplants work for us, compared to starting these seeds in flats in the greenhouse. It doesn’t work for lettuce at this time of year though – the tiny plants are too fragile and tender.

Vates kale seedlings in our hoophouse for bare-root transplanting outdoors.
Photo Pam Dawling

Follow-on Winter Hoophouse Crops

This is a  sequence of different crops occupying the same space over time. We try to keep the hoophouse fully planted all the time, and one aspect of this is knowing what we are going to sow when we pull an old crop out. Here’s our winter list:

  • 11/17: We follow our 1st radishes with 3rd  scallions
  • 12/23: 1st baby brassica salad mix with 5th radishes
  • 12/31: Some of our 1st spinach with our 2nd  baby lettuce mix
  • 1/15: Our 1st tatsoi with our 4th spinach
  • 1/16: Our Tokyo Bekana with spinach #5 for planting outdoors
  • 1/24: Our pak choy & Chinese cabbage with kale & collards for outdoors
  • 2/1: Our 2nd radishes with our 2nd baby brassica salad mix
  • 2/1: Our 1st Yukina Savoy with our 3rd mizuna/frilly mustards
  • 2/1: Some of our 1st turnips with our 3rd baby lettuce mix
  • 2/1: More of our 1st spinach with dwarf snap peas

Cooking Greens to Transplant in Central Virginia in January

Outdoors, we transplant nothing.

In the hoophouse, we fill gaps that occur in the beds. We replace spinach with spinach, brassicas with brassicas wherever possible. We use the Filler Greens which were sown October 10 and October 20 (brassicas such as senposai, Yukina savoy and the frilly mustards) and October 24 and November 9 (spinach). In December I mistakenly said that December 25 is our official last date for using the brassica fillers because there is not enough time for them to make worthwhile growth before they bolt. But I really meant January 25! Sorry!

  • Until January 25, fill gaps with Asian greens, spinach or lettuces as appropriate to match their neighbors.
  • From January 25 to February 20 fill all gaps everywhere with spinach transplants, except for places that will be sown in new crops in February.
  • From February 20, only fill gaps on the outer thirds of the beds, leaving the bed centers free for tomatoes, etc. in mid-March.

Other Cooking Greens Tasks in Central Virginia in January

We continue to harvest the hardier greens, and if (when) low temperatures are forecast, we might decide to clear the vulnerable crops and put them in the cooler.

See Cooking Greens for November for more details on winter-kill temperatures

During December we had two nights at 17°F (-8.5°C). The Koji are looking quite damaged. We grew more of this than we could eat before temperatures got too cold. Next year I hope for a return to the more cold-tolerant Yukina Savoy instead. We have not covered the spinach, because of issues with rowcover fibers getting in the food, and we’ll see how much production we get without rowcover. I’m expecting it to be a lot less, as spinach (like kale and lettuce) makes some growth whenever the temperature is 40°F (4.5°C) or more. That happens much more often under rowcover on sunny days than in the open. Savoyed spinach which we prefer) is hardier than smooth-leafed varieties. 10°F (-12°C) could kill the larger leaves and 5°F (-15°C) could kill it off entirely. This would be unfortunate as we expect to harvest a lot from out over-wintered spinach in the spring. Maybe temperatures won’t get that cold this winter, but I’m not holding my breath. Some spinach (Bloomsdale Long Standing, Bloomsdale Savoy, Olympia) is hardy down to 0°F (-18°C). We, however, have not been focused on growing the variety with the best absolute cold-tolerance.

Our chard is pretty much dead. The green is hardier than the multi-colored, which died a while back. Green chard is hardy to 12°F (-11°C), but ours is already weather-beaten. Because we have nice chard in the hoophouse, we no longer try to preserve the outdoor crop in winter.

I’m expecting January temperatures to bring the outdoor Koji and senposai to an end.

Spotting cabbage seedlings from a seed flat into a transplant flat.
Photo Wren Vile

Special Cooking Greens Topic for January: Lots of Planning!

We get our Crop Review, Seed Inventory and Seed Orders out of the way before the end of the year, then dive in during January to line everything else up for the next growing year. We use a lot of spreadsheets, and also maps and lists. First we prepare our new Seedlings Schedule, then our complex Fall Brassica Spreadsheet and Map, Field Planting Schedule, Hoophouse Schedule for March to September crops (those are not cooking greens!), and then our Raised Bed Plan and our monthly Garden Calendar.

The Seedlings Schedule Spreadsheet is most pressing, as we start greenhouse sowings in mid-January. Updating the spreadsheet from last year’s to create the new spreadsheet takes us three hours, plus proofreading and corrections. As we go, we make a list of questions or points to fix later, and we use highlighter on cells with unsure data to go back to. Our seedlings schedule has a column for the planned sowing date, one to write in when we actually do that sowing (in case it’s different), columns for the germination date, and the hoped-for transplant date, the vegetable, variety, how many row feet we want to plant, how many plants we will transplant in 100ft, and then a column with a calculation of how many plants we want to grow (allowing 20% extra on most crops). We will be spotting our transplants into flats of 40 plants, so next we calculate how many spotted flats we will need (simply the number of plants divided by 40). From that we calculate how many seed flats to sow. We reckon on getting 6 spotted flats from one seed flat, so again it’s a simple division. And we round up.

For crops that we sow in cell-packs (plug flats) we add another 20% to the Plants number. Lots of things can go wrong in January and February and we want to be sure to have enough plants. Also a lot of these early cell-packs are tomatoes for the hoophouse and we might want 15 different varieties.

All our spreadsheets have a Notes column, either with a pre-recorded reminder or hint, or with space to write in anything unusual or a different idea for next year. We check this and revise the sowing and transplanting dates accordingly.

Once we have the new spreadsheet set up, we get ready for the slow part of the job. One nice thing about spreadsheets is that you can sort the data each time you want a different perspective. We want to end up with a schedule in date order, but as far as feeding in the crop data, an alphabetical list by crop is much easier.

First we go through the current year’s Seed Order updating Varieties and Row Feet. Then we go through the Seed Order line by line, cross-checking to ensure that everything ordered gets sown (crops for transplanting only).

When we’re satisfied with that, we resort the data by transplant date, then by Vegetable, then Variety. We take the previous year’s Outdoor Planting Schedule (Field Planting Schedule) and revise the Seedlings Schedule accordingly.

Before we’re done, we check the highlighted cells and resolve any unresolved issues on our piece of paper. We check germinator shelves in use on any one day: We have space for 24 flats at once. Check the number of Speedlings in use at one time, we have 27. We refer to last year’s Seedlings Schedule for days to germination.

With all that work done, we can resort the data by Sowing date, then by Vegetable, then Variety. We proofread for sense before tidying up the formatting, and making sure all the columns fit on one sheet. We revise the instructions before we forget!