Year-Round Hoophouse Book update, Growing for Market, Mother Earth News post

 My upcoming book The Year-Round Hoophouse is being copy-edited this month. I was lucky enough to get the same copy-editor who I worked with on Sustainable Market Farming. Meanwhile the designer is working on the layout design, and a bookmark. I already have the pre-publication postcards to give away at events I attend. See my Events Page for that information.

My hoophouse book will be published November 20, which means it will come off-press (all being well) on October 12. Between now and then, we will finish the copy-edits, proofread for errors, then go back to the designer to enter the corrections (in June). In July the index gets made, by one of the Twin Oaks Indexing crew. That can take three weeks. Then there’s a last check (August) before the book goes off to the printers. The press needs five weeks to turn the book around (September and some of October). Meanwhile the electronic version (Ebook) is prepared.

The foreword will get written, as will those endorsements you see on book covers from well-known people who have been given a copy of the advance page proofs to read. Also happening is a lot of attention to marketing–sending information to the sorts of people who will be interested in the book.


The May issue of Growing for Market is out. The cover article is about wholesaling, by Jed Beach. His purpose is to encourage growers who are dissatisfied with the stiff competition in retail, to look carefully at comparative costs of selling wholesale. Receiving a lower price (wholesale) will not lead to lower income if you costs are considerably lower.

High Mowing Seeds is sponsoring farmer emeritus Ellen Polishuk to travel the country interviewing farmers for a Farmer to Farmer Profile series, which will be featured in Growing for Market each month.  This month her profile is of High Ground Organics in California, just two miles from the ocean. As well as the climate, Ellen tells us about the state laws that require overtime to be paid at 1.5 times the regular wage, and the requirement for wages for agricultural work to line up with other employment and achieve a minimum wage of $15 in six years’ time. This is causing big increases to labor costs. In addition, the national political situation is causing fewer immigrants to reach the farms. Hence, some farmers are selling up. The farmers at High Ground are selling one of their two farms in order to focus on farming one well. Eco-stewardship is an important value.  They are excited about improving at managing people and weeds, transitioning to only organic seeds, and growing strawberries with anaerobic soil disinfestation (ASD).

Photos of all the  farms featured in Profiles are here.

Ellen has written an upcoming book, with Forrest Pritchard, called Start Your Farm.It will be published in September 2018.

Morgan Houk compares a trip to the accountant very favorably with a trip to have teeth pulled. She encourages all farmers to learn from an accountant:

“the financial success of my business is critical in order for me to continue building community and growing healthy food”

 

Kai Hoffman-Krull writes about two no-till methods: tilling with chicken tractors, and occultation (the cumbersome name of a system using impermeable plastic silage covers to kill weeds and cover crops and leave the soil ready-to-use). The main purpose of using no-till methods for Kai is to keep the carbon in the soil, as both social and environmental activism.

Gretel Adams closes this issue with her usual solid information on growing cut flowers, This issue the topics are ranunculus and anemones. As always, the flower photos are mouth-watering.


A hose with pinholes repaired using bicycle inner tube and old repair clamps. Photo Pam Dawling

I have a new blog post on Mother Earth News This one is a tip for repairing pin-holes in garden hoses. Cheap hoses don’t spring pin holes, they just crack up. But if you invest in good quality hoses, eventually they start to develop pin holes. Cutting the hose and inserting a repair connector is unnecessary. You just need a leftover clamp from a repair coupling (I found I had a whole boxful!) and a square of inner tube. Mark the hole before turning off the water. Wrap the rubber inner tube over the hole, then assemble the old clamp over that.


Meanwhile in the garden this week, we have transplanted tomatoes outdoors, as well as the first cucumbers. The first lettuces are almost ready to harvest, just as the last hoophouse lettuce mix is getting less desirable – milky sap, slightly bitter flavor. We’ve planted out six sowings of lettuce so far. We’ve hilled the potatoes and disked lots of areas for sweet corn and  sweet potatoes.

Lettuce bed in May.
Photo Wren Vile

Tools for small-scale growers

Rolling drip tape on shuttles for storage and reuse.
Photo Luke Stovall

It’s been raining all day, so I look around for inspiration and useful rainy day work. Repairing things and making useful tools are usually satisfying.And I found a couple of fun and inspiring inventions by others to share.

Drip tape shuttles and winding system

I’ve written before about our drip tape shuttles, which enable us to save and reuse drip tape. Here’s our Perfect Drip Tape Pack-up Check List

  1. Gather spring clamps (4 per cart), rebar axles, carts, small bucket for end caps, black marker, yellow or white grease pencil (in Drip Tape First Aid Kit), a few pieces of rope 2-4 ft long.
  2. Remove end caps and collect in small buckets
  3. Remove any rope/cord tying drip tape to end stakes (if any)
  4. Pull up stakes
  5. Disconnect drip tape at main pipe, by unscrewing the connector from the tape, not by pulling the connectors out of pipe. Don’t disconnect any short drip tape blank ends, leave them in the pipe.
  6. One person coils the mainline pipe in big 4-5 ft diameter loops, with NO kinks. Tie in three places with rope. Make and affix a plastic label if there is not already one attached. Describe what crop it was used for, and what row spacings, number of rows. Store.
  7. Meanwhile, other people free up the drip tape without destroying the crop too much, and write the length on the ends, using the grease pencil.
  8. Set up the cart with the axle and spring clamps, on the uphill side of the patch (helps drain the tape as you roll it)
  9. Then roll it on appropriately labeled shuttles, two lengths at a time, tightly and tidily, each keeping to cos own side of the shuttle (so they can be unwound separately). Tuck last end in, and ensure the end of the drip tape is labeled with the length, and both sides of the shuttle are labeled.
  10. Take all the shuttles to the barn, and hang them in pairs over the beams using rope. Use knots that a normal human will be able to undo easily. Hang shuttles high enough so people won’t bang their heads, but low enough to be reachable by someone standing on a chair.
  11. Return all the tools and supplies.

Unrolling drip tape from shuttles, using a garden cart as support.
Photo Luke Stovall

I was reminded of our drip tape system when I came across this Rowcover roller

Rowcover rolling with crank handle.
Photo Rodale Institute

Taming the floating row cover is a blog post on the Rodale site by John and Aimee Good. They say

The row cover reel is our favorite part of our system, and it is super low-tech. It is comprised of two portable saw horses with pipe straps attached and a PVC crank we made to fit on the end of the row cover pipe. We set up the saw horses at the end of the bed about eight feet apart. We then push the PVC pipe through the pipe straps on each saw horse and hammer our crank onto the end of the pipe with a rubber mallet.

By using long pipes to roll the row cover on, they have handles to hold, and a space to label length, width, condition of the row cover.


While researching a term new to me: “Personalized Harvie Farm Shares

I learned from the Small Farm Central blog that Harvie connects customers directly with  local farms who deliver shares of farm fresh produce customized to meet personal preferences. Like a CSA, but with choices.


Towards the end of that post I got a chuckle when I saw this flame weeder:

Repurposed stroller makes a fine flame weeder.
Photo Sustainable Harvest Farm Kentucky

The blog post is entitled

3 Themes from 2,000 miles of driving visiting farms in TN and KY

and the inventive farmers Ford and Amanda are from Sustainable Harvest Farm in Kentucky.

I’ve written before about the wonders of flame weeding. We bought our Red Dragon backpack flame weeder from Fedco.

We’re going to need the stroller! Single-torch flamer saves lots of weeding time.
Photo Kati Falger


Broadfork from Way Cool Tools.
Photo Way Cool Tools

Another tool we love is our all-steel broadfork from Way Cool Tools.

I wrote about it last September, when we were preparing our hoophouse beds for winter crops.

This tool is great for aerating compacted soil without inverting it. The soil beasties thank us.

Below is a photo of a hoophouse bed after broadforking before the (immediately following) task of raking to break up the big clumps and produce a fine tilth. It’s important not to let the soil dry out into bricks before raking, or life will be hard (and those soil beasties may be dead).

Hoophouse bed broadforked to aerate the soil without inverting.
Photo Pam Dawling


Lastly I’ll mention our blueberry hoop method. Maybe your bushes, like ours, are flowering now, and maybe you are determined to have a better netting system than you had last year. I described our (then new) blueberry hoop system in 2013. The blueberry area is 16′ x 65′ approx. Height of the netting supports needs to be 7′ or more for most of the space. The 20 blueberry bushes are 66″ apart, in two rows.

We chose PVC Electrical conduit to make our hoops. Unlike PVC water pipe,  plastic electrical conduit is UV-inhibited for outdoor use. Lengths have flanged (bell) ends, and can be joined without any connector pieces. It’s lightweight, and no bending tools are needed (unlike for metal conduit or fencing top-rail). It packs flat for out-of-season storage, and is relatively cheap.

We made a “Spider-House” temporary framework: An idea used for temporary “field houses”. It consists of pairs of bows fastened together at the apex, in a way that spreads out into a 4-legged structure. A row of these make up the frame. An advantage is that the spiders are stronger than simple bows, and that the whole thing can be dismantled relatively easily. The shape helps add strength to lightweight bows.

Blueberry netting on hoops.
Photo Bridget Aleshire

Asian Greens for April: Mizuna and ferny mustards

Green mizuna in its prime in our hoophouse in November. Photo Pam Dawling

In April, sadly, our last mizuna and ferny mustards will come to an end. In our hoophouse we do three plantings of these frilly leaved greens, which we use for salads all winter and early spring.

Mizuna (also known as kyona  and shui cai) is a Brassica rapa var. japonica, meaning it’s in the turnip family. The other frilly mustards, such as Ruby Streaks, Golden Frills, Red Rain are Chinese Mustards, B. juncea. We tend to treat them as if they are all types of mizuna. True mizuna is available in green or purple (but Ruby Streaks and Scarlet Frills mustards are much better colors than Purple Mizuna.)

Golden Frills and Ruby Streaks in our hoophouse in February.
Photo Pam Dawling

All are very easy to grow, can be transplanted or direct-sown, and tolerate cold wet soil. They are ready to be harvested for baby salads only 21 days after sowing in the fall (longer in winter). They grow to maturity in 40 days. They are easy-going vegetables, fairly heat tolerant (well, warm tolerant) and cold-tolerant to 25°F (-4°C).  All regrow vigorously after cutting. The ferny leaves add color and loft in salad mixes, as well as an attractive leaf shape.

Mizuna is very mild-flavored. The ferny mustards vary in pungency, but most only become markedly spicy when they start bolting.

Like all Asian greens, they need similar care to other brassicas, doing best in very fertile soils. They are shallow-rooted – pay extra attention to providing enough water during hot weather to prevent bitter flavors and excess pungency, especially with the B. juncea ones. Provide 1” (2.5 cm) of water per week, 2” (5 cm) during very hot weather.

Do close monitoring of pests, which can build up large populations during the summer. Growing these over the winter, as we do, we have not had many pest problems. Flea beetles sometimes, once the weather starts to warm.

Young Ruby Streaks (our second planting) in our hoophouse in early February. We thin for salads until the plants are at final spacing.
Photo Pam Dawling

Our mizuna schedule

On September 24 we sow these little crops in our outdoor nursery seedbed, which is covered with insect netting on hoops. We sow 7.5′, with roughly equal amounts of Green Mizuna, Golden Frills, and Ruby Streaks or Scarlet Frills. Red Rain is another we like. We are aiming for about 75 transplants on October 20. We transplant them 8″ apart with 6 rows in a 4′ bed. This takes 8′ length of a bed. This first planting will feed us from November 27 to January 25, with light harvests possible from November 5, and flowers and sprouting shoots as late as February 10.

Our second planting is direct sown in the hoophouse on November 9. We sow 6 rows about 6′ long (depending on available space). We thin these into salad mixes several times as they grow, increasing the spacing until they are about 6-10″ apart. After that we harvest by cutting off the larger leaves, sometimes individually, sometimes by “buzz-cutting” (snipping off leaves on one half of the plant an inch (25 mm) above the ground). Leaving half of the leaves growing seems to help the new leaves grow faster. Next time we harvest, we cut the other side. This planting provides harvests from February 26 to March 24 – just one month, although we get the thinnings from January 20, and the flowers and bolting shoots until mid-April.

Our third planting, green mizuna and Scarlet Frills, in our hoophouse in mid April. The mizuna is bolting, but the Scarlet Frills is hanging in there.
Photo Pam Dawling

A couple of years ago we added in a third planting, because we had some open space in the hoophouse. It follows the first Yukina Savoy. I wrote about some differences between the OP Yukina Savoy and the hybrid Koji. Perhaps Koji is less bolt-resistant than the OP. Late January brings it to an end.

We sow this third planting on February 1 and harvest it for a month from March 24 to April 23. This year this third planting is bolting April 15. (We have had a lot of temperature reversals this spring, which encourage bolting in brassicas.) Scarlet Frills and Golden Frills bolt later than Ruby Streaks and Green Mizuna. The timing of harvest fits perfectly with the second planting. We have sown it as late as March 3 and harvested April 10-April 30 (only 3 weeks when we sow that late).

Seed sources

Kitazawa Seeds sell 18 baby leaf mustards, including four red, purple or streaked mizunas. The other 14 are B. juncea, although a few don’t say. Most are frilly or ferny, a few merely wavy. Something for everyone.

Johnnys lists their selection under “Greens” along with arugula, large Asian greens, mixes. I counted about 15 mustards that fit the loose category I’m talking about here.

Fedco lists theirs under “Asian greens”. Scroll down past Mizuna to Mustards to find several interesting gene pool offerings such as Pink Lettucy Mustard (Variations of greens with pink or purple pigments in midribs) for those seeking milder flavors; and the medium hot Purple Rapa Mix Gene Pool (sold out as I write this): Very vigorous tall serrated green leaves with purple veins and shading.

Bye bye mizuna! Bolting mizuna (our third planting) in our hoophouse in mid-April.
Photo Pam Dawling

This is my twelfth and last Asian Greens of the Month series. You can see the others here:

May Senposai outdoors

June Tokyo Bekana

July Maruba Santoh

August Fall Senposai, winter Yukina Savoy

September Komatsuna outdoors

October Yukina Savoy outdoors, Tatsoi

November Daikon and other winter radish

December Pak Choy

January Chinese cabbage

February Tatsoi

March Yukina savoy in the hoophouse

Next month I’ll start another year-long series Allium of the Month

Spinach Variety Trials and Planting Plan

Avon spinach in our hoophouse October 25.
Photo Pam Dawling

For years we grew only Tyee savoyed spinach. It did very well for us in central Virginia. It survived our zone 7a winters outside under rowcover. It could survive without the rowcover, but given that spinach makes growth whenever the air temperature is above 40F, and that the air under rowcover reaches that a lot more often then the air outside, we got much more growth using rowcover. We also got much better quality leaves, as they didn’t get battered by the weather.

Tyee is bolt-tolerant too but tended to yellow, slightly tough, leaves in the fall.

Tyee was dropped as a variety by the growers because (as I understand it) it suffered from a disease that is prevalent in the Pacific Northwest, where spinach seed is grown. It’s a hybrid, so we can’t just save our own seeds. We set out to try other varieties in order to find something to replace our beloved Tyee.

I wrote about spinach varieties here  in October 2016.

We tried Chevelle and Avon. Chevelle didn’t do that well for us. Part of the problem was poor germination, which could have just been that one packet of seed. But the pressure was on to find a productive variety, so we gave up on Chevelle.

We strongly prefer savoyed spinach over flat leaf spinach, because it has more loft in salad mixes and is more wilt-resistant after harvest. Apparently the East coast prefers savoyed spinach and the West coast the flat leaf kind, for what that’s worth. And of course, that takes no account of the millions of people between the coasts!

Reflect spinach from a September 12 sowing, outdoors under rowcover after the -9F night in early January.
Photo Pam Dawling

Next we tried Avon and Reflect, and they seemed pretty similar, both have good flavor.

Avon (42 days mature, 20 to baby leaf) semi-savoyed F-1 hybrid with upright growth, https://www.fedcoseeds.com/seeds/search?item=2538. Fedco likes Avon as a replacement for Tyee, but cautions

“We found Avon’s DM [Downy Mildew] resistance is not adapted to overwintered protected culture. Otherwise resistant to DM1,2 and CMV [Cucumber Mosaic Virus].”

Sounds like it might not do as well if water supplies run short once it gets hot. Bolting is initiated by heat, crowding and day-length over 14 hours. Avon claims strong bolt resistance.

Reflect (38 days to mature) semi-savoyed hybrid is recommended by Johnnys as a good alternative to Tyee. It has much more resistatnce to various Downy Mildew strains (1-11, 13, 15, 16), but is “slightly” faster bolting than Tyee. This factor could be set against its very fast growing rate. Its color is a medium-green, less dark than some other varieties.

This winter and spring we are trying Avon, Reflect, Renegade, Escalade and Acadia.

Renegade (43 days mature) smooth leaf hybrid. Slower growing than Corvair, which it resembles in flavor. Does well in chilly damp conditions (our winter hoophouse?) Has resistance to DM 1-7. Bolt-resistant, dark green leaves.

Escalade (43 days mature) slightly savoyed hybrid, with upright growth, claims high bolt resistance. Resistant to DM 1-14, 16. Slower growing than some. Expected to handle temperature and light variability. Good for baby leaf production (not what we do). The flavor is mild (not a good thing, for those of us who love spinach!) Will it grow fast enough in our short springs to give high yields before it bolts? We’ll let you know.

Acadia (45 days mature) slightly savoyed hybrid with upright growth. Resistant to DM 1-13, 15, 16. Even slower growing than Escalade, even more suited to baby leaf production

Our second sowing of hoophouse spinach. Left row Avon, then Acadia, then Escalade, with Renegade nearest the plastic. Sowed 11/8, photographed 2/5.
Photo Pam Dawling

Paul and Sandy Arnold in Argyle, New York, made a great slide show reviewing  Spinach Varieties in High Tunnels

The winners (in order) in terms of yield were Pigeon, Space, Giant Winter, Tyee, Palco. These were followed, after a noticeable drop in yield, by Raccoon, Renegade, Donkey, then another noticeable drop to Corvair, Regiment, and a plummet to Bloomsdale Longstanding and Samish. Giant Winter and Bloomsdale Longstanding are the only OPs in the list. We grew Giant Winter once. It did grow enormous leaves, but was very quick to bolt. Unsuited to repeated harvests in our climate.

In 2011-2012, High Mowing Seeds in northern Vermont did a spinach variety trial with 24 varieties, assessing productivity, color and harvest time. The 24 varied a lot in earliness, upright growth habit or not, flat or savoyed leaves, and level of pest resistance.

On color, America, Corvair, Crocodile, Donkey, Emilia, Lazio, Menorca, Queen, Raccoon, Red Kitten, Regiment, Samish, Seven Green, Space, Spargo, St Helens and Tyee scored 7 out of ten or better. Tyee only scored 7, Reflect only 4-5. The best were Corvair and Crocodile.

  • Corvair had a good color and upright growth (clean leaves, easy to pick).
  • Donkey was dark and productive.
  • Emu was an early producer with a better color,
  • Giant Winter was a great early producer although poor on color (and terrible on bolt-resistant when we grew it in Virginia).
  • Lombardia was good on yield and flavor,
  • Raccoon was one of the easiest to pick,
  • Red Kitten (red stems) was pretty and heavy but not high yielding,
  • Reflect was a good survivor in heavy rains,
  • Regiment gave high yields and had a good green color.
  • Space was one of the highest for yield,
  • Samish was good on yield and OK to pick,
  • Tyee had good savoy-ness but lower yield, although many other good points.

Our first sowing of spinach in the hoophouse, photographed in late September. Reflect on the left, Avon on the right.
Photo Pam Dawling

Here’s our spinach planting plan:

We are able to keep harvesting spinach from October 15 to May 25, all the way through the winter.

September 6 is our first sowing (sprouted seeds) in the hoophouse for winter harvest 10/30-2/15,

We sow outdoors on September 7 (sprouted seeds) for growing under rowcover and harvesting in fall and winter,

September 18-20 we sow in our coldframes and outdoors for harvest in early spring, until late May,

October 24 we make our second hoophouse sowing, to feed us November 25 to May 7. In 2017, we failed to water this planting enough, and had to resow November 8.

November 9  we make a third hoophouse sowing, intending to use these plants to fill gaps in our hoophouse as other winter crops come to an end.

January 16 we make more sowings in the hoophouse, some to continue to fill gaps there along the edges of the beds where they won’t fight with the tomatoes and so on, which we transplant starting March 15.

Most of the spinach sown this date is for transplanting outdoors February 21.

January 29 we sow in flats in the greenhouse if we see we haven’t got enough bare-root transplants in the hoophouse.

If we don’t have enough transplants, then on February 10 we sow outdoors with rowcover, for spring harvests until May 25 if we’re lucky. We have backup plans on backup plans for this!

In the hoophouse we continue transplanting spinach to fill gaps until March 31.

Hoophouse spinach #2. Front row (bottom of the picture) Acadia then Escalade then Renegade.
Photo Pam Dawling

 

Winter-Kill Temperatures of Cold-Hardy Vegetables 2018

Here’s the long version of one of the slideshows I presented on January 13 at the Future Harvest CASA conference. Since I got home, I updated my Winter-Kill Temperatures list, which appears in the slideshow. Compared to my list for 2016, there are a few differences, nothing major. We had some extremely cold weather, as I reported last week with some sorry pictures of lettuces. Now I have some photos of the outdoor crops too. The Vates kale had mixed survival, the rowcovered Reflect and Avon spinach are damaged but OK, the Tadorna leeks are battered but hanging in there (so are we!).

Vates kale which survived temperatures of -8F and -9F outdoors, uncovered.
Photo Pam Dawling

Vates kale with a freeze-killed center January 19 2018.
Photo Pam Dawling

For several years I have been keeping records of how well our crops do in the colder season. I note each increasingly cold minimum temperature and when the various crops die of cold, to fine tune our planting for next year. We had some extremely cold temperatures of -8°F and -9°F (-22°C and -23°C) in early January 2018. We are in zone 7a, with an average annual minimum temperature of 0-5°F (-18°C to -15°C).

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, micro-climates and rain levels may lead you to use different temperatures in your crop planning.

Hoophouse Notes

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

In the hoophouse (8F warmer than outside) plants without extra rowcover can survive 14F colder than they could survive outside; 21F colder than outside with rowcover (1.25oz Typar/Xavan).

For example, salad greens in a hoophouse can survive nights with outdoor lows of 14°F (-10°C) without inner rowcover. Lettuce, mizuna, turnips, Russian kales, Senposai, Tyee spinach, tatsoi, 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 hardy enough for a solar heated winter 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, 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.

35°F (2°C):  Basil.

32°F (0°C):  Bush beans, 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, chicory roots for chicons, and hearts, Chinese Napa cabbage (Blues), dill (Fernleaf), endive (Escarole more frost-hardy than Frisée), 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.

Spinach under rowcover, with our hoophouse in the background – crop protection pays!
Photo Pam Dawling

22°F (-6°C): Some arugula (some varieties are hardier), Bright Lights chard, large leaves of lettuce (protected hearts and small plants will survive colder temperatures), rhubarb stems and leaves.

20°F (-7°C): Some beets (Bulls Blood, Chioggia,), broccoli heads (maybe OK to 15F), Brussels sprouts, some cabbages (the insides may still be good even if the outer leaves are damaged), celeriac, celtuce (stem lettuce), some head lettuce, some mustards/Asian greens (Tendergreen, Tyfon Holland greens), flat leaf parsley, 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, endive, 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) if not covered, broad leaf sorrel, most covered turnips, winter cress.

12°F (-11°C): Some beets (Cylindra,), some broccoli, 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, most fall or summer varieties of leeks (Lincoln, King Richard), large tops of potato onions, covered rutabagas, Senposai leaves (the core of the plant may survive 10°F/-12°C), 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, 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), large leaves of savoyed spinach (more hardy than flat 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 savoyed 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).

Tadorna leeks, struggling but not dead, after -9F.
Photo Pam Dawling

0°F (-18°C): Chives, some collards (Blue Max, Winner), corn salad (mache), garlic, horseradish, Jerusalem artichokes, 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, Tyee). 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 die, Vates kale survives although some leaves may be too damaged to use.

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

-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

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

A cover crop of winter wheat untroubled by -9F.
Photo Pam Dawling

Book Review, The Bio-integrated Farm by Shawn Jadrnicek

Publisher: Chelsea Green. ISBN: 9781603585880

This book, by Shawn and Stephanie Jadrnicek, was hidden in my “to read” pile for too long! The title doesn’t make it clear enough that this is an authoritative text on all kinds of water management on the farm: integrating ponds, swales, ditches, water catchment, heat storage in water, irrigation, water for light reflection in winter, fish and shrimp-farming. Chickens and black soldier flies, compost-making and vegetable production in hoophouses and outdoors are all part of the bigger picture.

This book speaks from Shawn Jadrnicek’s experience at the Clemson University Student Organic Farm in South Carolina, and at his own homestead. The author tells us honestly when things he tried didn’t work out, and why. It is a permaculture book written for non-believers as well as the converted. It does not mystify with strange jargon. It does not make unsubstantiated claims about how things ought to be. Full disclosure: I suffer from having read too much permaculture writing that was obscure, convoluted, not backed with direct experience and written for people with a lot of time and only a small piece of land. This book is a breath of fresh air! The ideas have been tested on a farm scale, with a close eye on efficiency. It’s written for market farmers, homesteaders and serious gardeners, showing how to make best use of natural resources to help feed the world. Each technique has to have at least seven functions to qualify for inclusion in the author’s farming practices and the book.

You may not want to follow all of the author’s methods. I, for one, am not going to grow hydroponically. (I doubt that fully nutritious food can be grown without soil, with just the nutrients we know to feed in.) You may not want a hoophouse that is almost all pond. But you may be very happy to find a book that describes how to build a hoophouse on sloping land; very happy to learn how to grade your land to move rainwater away from where you don’t want it to sit, to where you do want it to improve growth of your pastures. You may be very happy to learn how to use a pond to grow minnows (tadpoles in the non-minnow season) to feed chickens. You may like the idea of filling your hoophouse with sweet potatoes or cowpeas in summer to act as a “smother crop,” dealing with weeds while keeping the soil alive. Perhaps you’d like to try freshwater prawn (large shrimp) farming? The regulations are easier than for fish-farming. Giant river prawns can weigh as much as a pound, they are easy to process and cook, and they sell at a good price.

Water management fills over half of the book, complemented by 30 pages on chickens, 33 on compost, 13 on fly farming, 28 on field layout and drainage, and 56 pages of case studies. Most of the vegetable production mentioned takes place in hoophouses (high tunnels). The book includes various ideas for heating the indoor crops, using hydronics (indirect heating with water in pipes warmed in outdoor ponds or compost piles), indoor ponds with solar pool covers, and compost piles leaning on the sidewall of the hoophouse. The information on rainwater harvesting includes checking your roofing material for toxicity (there is a special coating you can put on if necessary), how to avoid leaves clogging gutters (cleverly designed downspout filters), regulations about harvested rainwater, how to make gravity flow toilets and gravity drip irrigation systems that really work, and how to find the data and do the calculations. The level of detail in this book inspires confidence!

The chicken-farming system in this book uses a permanent coop and alley (mulched corridor) along with temporary pens made with electric netting. This makes better use of resources than free-ranging, unless you have only mature trees and grass. The birds get 30% of their dietary needs from the landscape, if rotated every 6-12 days onto perennial clover and grass pasture that has regrown to 4-8″ in height. This system ensures the chickens can always reach shade, and you can reseed bare spots in the resting pens with rye, wheat, millet, sunflowers and buckwheat, and reduce their feed costs by 30%. I liked the careful thinking and observation behind this scheme.

And then we come to the black soldier flies. The mesh flooring of the chicken pen lets the manure fall through into a fly digester below. The fly larvae digest the manure and grow, later becoming chicken food themselves. I wasn’t initially attracted to the idea of deliberately breeding flies, but the system has a lot going for it. Black soldier flies (Hermetia illucens) are not a pest. In fact they out-compete houseflies and thus reduce their numbers 95%! The adult soldier flies live only 5-15 days – they have no functioning mouthparts, and they don’t vector diseases. They are native in zone 7 and warmer, especially in the Southeast, so consult your Extension Service to find out if you’ll need to mail order them or just set out a nice digester once it’s warm enough. This sounds better than worm-bin farming! The flies tolerate a wider range of conditions and consume waste faster than earthworms. The large segmented larvae will “self-harvest” into buckets, if you have a well-designed digester. Two commercial models are available, the larger ProtaPod (4 ft diameter) and the smaller BioPod. They have internal ramps that the pre-pupae will climb, and a curled rim that prevents escape. The creatures launch themselves down a tube into a lidded bucket. All the details are in the book! Add fresh waste daily, and empty the bucket at least weekly (to prevent adult flies hatching out and setting up residence where you don’t want them).

The section on compost-making includes how to extract heat from your compost pile to warm your hoophouse, and how not to extract so much heat that the compost stops working. My beef with some other books about methods of heating greenhouses is that they fail to address the unintended side-effects, such as having very humid air go into your living space, or having little space left to grow plants because the greenhouse is full of heat-storing devices. Make good compost, and warm your hoophouse a bit.

The section on field application of these ideas is not about growing vegetables, but about field layout and drainage. It includes useful calculations on using drip irrigation. It also discusses keyline plowing, which had previously been just a bit of permaculture theory to me. Shawn says, “keyline pattern cultivating intrigued me for years, but I first had to implement the technique before becoming a convert.” There is no need to buy the special equipment some advocates suggest, if you have a box scraper with ripping tines. Keyline plowing (ripping 4″ deep in lines through pasture or grassways to direct water from a valley to a bit of a ridge) helps build soil and increase grass growth. Reading Shawn’s results, I now understand why others said it was a good idea.

I recommend this book to any small-scale farmers who are interested in learning efficient techniques to increase productivity while reducing use of resources.

Stephanie and Shawn Jadrnicek
Photo Chelsea Green

Garden Planning, Winter Harvests and Speaking Events

Garden Planning Field Manual
Photo VABF

‘Tis the season – after the relaxation of the holidays – time for garden planning. Inventory your seeds left from last year, peruse the catalogs and prepare your seed orders. The earlier you get them in, the more likely you are to get the varieties you want, before anything is sold out.

I notice that readers of my blog have been looking up the Twin Oaks Garden Calendar,  also known as The Complete Twin Oaks Garden Task List Month-by-Month. You can search the category Garden Task List for the Month, or you can click on the linked name of the month you want. At the end you can click on “Bookmark the Permalink” if you might want to refer to this in future. Remember, we’re in central Virginia, winter-hardiness zone 7a. Adjust for your own climate.

Meanwhile, despite the turn to cold weather, we are not huddled indoors all the time. Each day, one or two of us sally forth to harvest enough vegetables to feed the hundred people here at Twin Oaks Community. Outdoors, in the raised bed area, we have winter leeks, Vates kale, spinach and senposai. We could have had collards but we lost the seeds during the sowing period, so we have lots of senposai instead. Senposai leaves (the core of the plant may survive 10F), are hardy down to about 12F. I noticed some got a bit droopy when we had a night at 15F. Collards  are hardier – Morris Heading (the variety we grow) can survive at least one night at 10F.

Hoophouse December View
Photo Kathleen Slattery

In the hoophouse, we have many crops to choose from: lettuce, radishes, spinach, tatsoi, Yukina Savoy, Tokyo Bekana, turnips and turnip greens, scallions, mizuna, chard, Bull’s Blood beet greens.

Hoophouse scallions ready to harvest.
Photo Pam Dawling

Pak Choy and Chinese cabbage heads are filling out, ready for harvest in January.

Tokyo Bekana, a non-heading Asian green,  has large tender leaves, which we are adding to salad mixes. It can be used as a cooking green, but only needs very light cooking. It will bolt soon, so we are harvesting that vigorously, not trying to save it for later.

The kale and senposai in the hoophouse are being saved for when their outdoor counterparts are inaccessible due to bad weather. The spinach is added to salad mixes, or harvested for cooking when outdoors is too unpleasant, or growth slows down too much.

Hoophouse winter lettuce: Green Forest and Red Salad Bowl, two of our fifteen varieties.
Photo Wren Vile


Another kind of planning I’m doing right now is scheduling my speaking events for the coming year and practicing my presentations. Last week I updated my Events page, and this week I’m adding a new event: The September 21-22 Heritage Harvest Festival.

I might pick up a couple of events in late April and early June, but that’s just speculation at this point.

Right now I need to practice for the CASA Future Harvest Conference January 11-13. Cold-hardy Winter Vegetables and a 10-minute “Lightning Session” on using graphs to plan succession plantings for continuous harvest. Click the link or my Events page for more on this.

What Makes Potatoes Sprout?

Harvesting potatoes. Photo Lori Katz

“White” or Peruvian potatoes (sometimes called Irish potatoes) are stem tubers in the nightshade family; sweet potatoes are root tubers in the Morning Glory family. This article is about Peruvian potatoes, not sweet potatoes.

Curing potatoes

Potatoes are cured enough for storage when the skins don’t rub off. It’s best to leave the potatoes in the ground for two weeks after the tops die, whether naturally or because of mowing, if you want them to store. When the potatoes are harvested after the skins have toughened, there will be less damage during harvest. Curing allows skins to harden and some of the starches to convert to sugars. These changes help the tubers to store for months.

When potatoes first go into storage, they are still “alive” and respiring, and need fresh air frequently. They will heat up if left closed in, and could develop black centers, where the cells die from lack of oxygen.

Storing newly harvested potatoes

For the first two weeks after harvest, the root cellar or other storage space will need 6-9 hours of ventilation every two or three days. The temperature goal is 60°F–75°F (16°C–24°C), with 95% humidity. Ventilate when the temperature is 0–20F (0–11C) cooler than your goal: in the daytime if nights are too cold and days are mild; at night if nights are mild and days too warm. If it is very damp in there, ventilate more.

Two weeks after harvest, sort all the potatoes. By this time, any which are going to rot have likely started doing so. Restack, remembering to keep airspace between the crates and walls. For weeks 2–4, the temperature goal is 50°F (10°C) and fresh air is needed about once a week.

Potato crates in our root cellar.
Photo Nina Gentle

Long term potato storage

After week 4 in winter, cool to 40°F (5°C); in summer, below 50°F (10°C). Ventilation for air exchange is no longer needed, as the tubers have become dormant. The final long-term storage conditions are cool and fairly moist, 40°F–50°F (5°C–10°C), 85%–90% humidity—a  root cellar is ideal. Below 40°F (5°C) some starches convert to sugars, giving the potatoes a bad flavor and causing them to blacken if fried. Try hard to avoid having the cellar cool down, then warm up. That causes the potatoes to sprout.

Pre-sprouting seed potatoes

Potatoes have a dormant period of 4–8 weeks after harvest before they will sprout. The warmer the conditions after dormancy ends, the quicker they will sprout. If you want potatoes to sprout during the dormant period, trick them by refrigerating for 16 days, then pre-sprouting them in the light.

We routinely “chit” or pre-sprout our seed potatoes before planting. Bring the seed potatoes into a warm, well-lit room around 65°F–70°F (18°C–21°C) and set them upright in shallow boxes, rose end up, stem (belly-button) down, for 2–4 weeks in spring, 1–2 weeks in summer. For summer planting, store your seed potatoes in a cool place at 45°F–50°F (7°C–10°C) until 2 weeks before your planting date, then sprout them.

Seed potato pieces after pre-sprouting for planting.
Photo Kati Falger

The effects of ethylene

Ethylene is a naturally occurring, odorless, colorless gas produced by many fruits and vegetables, but it can also be produced by faulty heating units and combustion engines. Propane heaters should not be used, as propane combustion produces ethylene. Incomplete combustion of organic fuels can result in the production of carbon monoxide, ethylene and other byproducts. Do not use any unvented hydrocarbon fuel heaters near stored produce.

Ethylene is associated with ripening, sprouting and rotting. Some crops produce ethylene in storage—apples, cantaloupes, ripening tomatoes, already-sprouting potatoes all produce higher than average amounts. Chilling, wounding and pathogen attack can all induce ethylene formation in damaged crops.

Some crops, including most cut greens, are not sensitive to ethylene and can be stored in the same space as ethylene-producing crops. Other crops are very sensitive and will deteriorate in a high-ethylene environment. Potatoes will sprout, ripe fruits will go over the top, carrots lose their sweetness and become bitter.

Summary: Potatoes are more likely to sprout if they are more than 4–8 weeks after harvest; in the light; near fruits, vegetables, flowers or malfunctioning propane or natural gas heaters that produce ethylene; too warm, or warm after being cool.  Potato sprouts are toxic, see my earlier article.

Planting potatoes.
Photo Wren Vile

What Makes Sweet Potatoes Sprout?

Sweet potatoes crated in the field.
Photo Nina Gentle

The difference between Peruvian (“white”) potatoes and sweet potatoes

Peruvian potatoes (sometimes mistakenly called Irish potatoes) are stem tubers in the nightshade family; sweet potatoes are root tubers in the Morning Glory family. Stem tubers have buds, nodes and internodes, and scaly leaves, and the ability to develop chlorophyll when exposed to light. Root tubers do not have these attributes. This article is only about sweet potatoes.

The difference between curing and storage

Some vegetables need to cure before storage and the curing conditions are different from those needed for storage. Curing allows skins to harden and some of the starches to convert to sugars. These changes help the tubers to store for months.

Curing sweet potatoes

Within an hour or two after harvest, field drying, sorting and crating, take the boxes of sweet potatoes to a warm, damp indoor space to cure. Curing allows the skin to thicken, cuts to heal, and some of the starches to convert to sugars. Uncured sweet potatoes are not very sweet, will not bake well, and are best used in dishes with other foods.

In addition to promoting the healing of wounds acquired during harvesting and handling, the curing conditions are necessary for development of a protective cork layer over the whole root. And a waxy material (suberin) is produced by the root’s outer cells and covers the skin. This layer acts as a barrier to disease organisms, and prevents excess moisture loss.

Boxes of sweet potatoes curing.
Photo Nina Gentle

Curing involves optimizing three conditions: temperature, relative humidity and ventilation. Ideal curing conditions are 85°F–90°F (29°C–32°C), and 80–95% humidity for 4–7 days. Curing takes longer (as much as 3 weeks) if conditions are less than perfect. Dry air does not lead to good curing. If the air is below 66% humidity, timely good healing will not take place, and the sweet potatoes will not store well unless more time is allowed. The loss from decay in sweet potatoes cured at 50% is twice that of those cured at 82%. (Storage of sweetpotatoes, Jacob Martin Lutz, USDA, 1958)

In the past we used our greenhouse to cure sweet potatoes, but it really is too hot and sunny, and dry. Nowadays we use a heated basement. We stack our 4” (10cm) deep boxes of roots on pallets, with wood spacer bars between boxes in each stack, to ensure air flow. We use box fans to improve the airflow, and the basement already has some natural ventilation. We reckon on 10–14 days.

We get quite good temperatures, but keeping humidity up is difficult for us. We cover the flats with newspaper to hold in some moisture. Some people use perforated plastic. We have also used domestic humidifiers and we’ve tried hanging strips of wet cloth from the ceiling. The best result seems to come from splashing water on the concrete floor several times each day.

To test if curing is complete, rub two sweet potatoes together. If the skins scratch, they need to cure longer. Curing longer than needed leads to sprouting.

Sweet potato storage

Sweet potatoes can be stored in the same room they are cured in, but it is important to cool the room evenly and fairly rapidly from the curing temperature of 85°F–90°F (29°C–32°C),  to the storage temp of 55–60°F (13°C–16°C) in 10 days or fewer.

Above 60°F (16°C), shrinking, pithiness, and internal cork (a symptom of a viral disease) when the virus is present may occur, and below 55°F (13°C), a permanent chilling injury (Hard Core) can happen. The potatoes remain hard no matter how long you cook them, and are useless. Do not ever let the temperature drop below 50°F (10°C). Ideal storage conditions for sweet potatoes include 60–70% humidity, up to 85 %, with one air change each day. If the heat circulation is uneven, hot spots can develop in front of the heaters and cause severe losses. Never let hot air blow directly on the sweet potatoes. Do not store in airtight containers, sweet potatoes need one complete air change per day.

Ken Allan, in Sweet Potatoes for the Home Garden, informs us that at about 60°F (16°C), the metabolism of the sweet potato slows to near zero, meaning it won’t grow. Temperatures above 70°F (21°C) are conditions that allow growth: although slow at 70°F (21°C), the rate increases to fast at 100°F (38°C).

We use a rodent-proof “cage” in our basement. We stack the boxes directly on top of each other and this seems to keep enough moisture in. This way, assuming we had a good enough harvest, we can still have sweet potatoes into May and early June. Shrinkage occurs at 1–2 % per month if cured, 2–5 % if uncured. In some cultivars, pithiness also increases with length of storage.

Sweet potatoes do not need to be in the dark. Dormancy is generally broken by moisture and warmth, not daylight. Green sweet potato sprouts are edible, not toxic, as white potato sprouts are.

The effects of ethylene

Ethylene is a naturally occurring, odorless, colorless gas produced by many fruits and vegetables, but it can also be produced by faulty heating units and combustion engines. Propane heaters should not be used, as propane combustion produces ethylene. Incomplete combustion of organic fuels can result in the production of carbon monoxide, ethylene and other byproducts. Do not use any unvented hydrocarbon fuel heaters near stored produce.

Ethylene is associated with ripening, sprouting and rotting. Some crops produce ethylene in storage—apples, cantaloupes, ripening tomatoes all produce higher than average amounts. Chilling, wounding and pathogen attack can all induce ethylene formation in damaged crops.

Some crops, including most cut greens, are not sensitive to ethylene and can be stored in the same space as ethylene-producing crops. Other crops are very sensitive and will deteriorate in a high-ethylene environment. Potatoes will sprout, ripe fruits will go over the top, carrots lose their sweetness and become bitter. Sweet potatoes are sensitive to ethylene and should not be stored with any crops or any heating systems that produce ethylene. Symptoms are difficult to diagnose, but ethylene can cause internal darkening and pithy areas, as well as sprouting.

Accidental sprouting of sweet potatoes

If your curing or storage conditions were not right, you may get early sprouting. If this happens, snap off the sprouts and use the sweet potatoes as soon as possible. If the sweet potato also has soft and wrinkly flesh, it’s an indication that it has lost nutrients. Left longer, spouted sweet potatoes become mushy and turn brown or black.

Seed sweet potatoes growing slips.
Photo Kathryn Simmons

Intentional sprouting of sweet potatoes

Sweet potatoes that are intended for sprouting are kept under normal storage conditions, then conditioned for 2 weeks (or even 4), before you start to grow slips. Start 10–12 weeks before your planting date, conditioning at 75°F–85°F (24°C–29°C), 95% humidity for 2–4 weeks, then set to sprout. Set up a place with light, humidity and ventilation at 75°F–85°F (24°C–29°C) and 12″ (30 cm) of headroom.

Summary: Sweet potatoes are more likely to sprout if they were cured for too long; curing conditions were too far from ideal; temperatures stayed too high—above 60°F (16°C)—once the sweet potatoes were cured (especially at high humidity); they were exposed to low temperatures followed by higher ones; they were physically damaged or stored near ethylene sources.

Sweet potato harvest
Photo Nina Gentle

Soil tests and high phosphorus levels

I just got back from the Carolina Farm Stewardship Association Conference, where I had a great time. I will be posting my slideshow Sequential Planting of Cool Season Crops in a High Tunnel here next week, after I’ve added back in some of the material I had to cut to fit the time slot. Meanwhile here’s some in depth thoughts about phosphorus levels, an issue for those of us who pile lots of animal manure or compost on our gardens.

Soil pH analysis machine at Virginia Tech.
Photo from Virginia Tech

This is the best time to get a Soil Test

            Get an annual soil test in the fall, from the same agency each time—different labs sometimes use varying test methods. Also, soil collected in spring is usually higher in P than soil collected in the fall. Consult an agronomy book, your extension service, or a live agronomist for help in interpreting your test results. Most soil tests don’t include a measure of organic matter as this can vary a lot from week to week. My state extension service provides standard tests for soil pH, P, K, Ca, Mg, Zn, Mn, Cu, Fe, B, and estimated CEC, plus a fertilizer and lime recommendation. For a small fee there are special tests for soluble salts and organic matter.

Amendments and the Issue of High Phosphorus

High levels of soluble salts, including nitrate, potassium, and sulfate from fertilizers or organic materials like compost can build up and stunt plant growth.  Some of the salt problems are caused by having very high organic matter levels, due to heavy amendment with composts or manures. In high OM soils, when warm or when irrigated after a dry spell, large flushes of nitrate can occur. This makes it difficult to manage nitrogen levels.

Organic soil amendments include soil inoculants, organic mulches, biochar and other soil conditioners, lime and other natural minerals, manure and other organic fertilizers, such as alfalfa meal, soybean meal, fish meal, kelp, composted chicken litter and compost.

Screening compost from a huge pile, for spring seedling compost.
Photo Wren Vile

Most growers are lavish with compost when they can be. Good quality finished compost is a way to add organic matter and nutrients. Compost can add a range of beneficial bacteria and fungi, which can inoculate plants against diseases by inducing systemic acquired resistance. The plants produce antibodies and other protective compounds before any infection can occur. Compost improves the soil structure, organic matter and humus. The effects last longer than cover crops and crop residues, especially in humid conditions where the breakdown of plant material is very rapid.

How much compost is too much? Some of us were raised to think of compost as the gold standard soil improver, and find it hard to believe there can be too much of a good thing. Others may consider compost like salad dressing—something to add that je-ne-sais-quoi to a good meal.

Compared with poultry litter compost (lower C:N  ratio), on-farm mixed compost (high C:N) leads to higher total soil organic C and N, higher N mineralization potential and better water infiltration. Poultry litter compost can enhance organic matter and N mineralization potential over conventional systems, but can lead to excess P. In terms of organic matter, composted manure is better than uncomposted solid manure, and both add more than slurry manure (which provides very low C:N; and half of the N is ammonium).

Manure and compost can add too much P relative to N and K. It is worthwhile to understand the effect of phosphorus.

Phosphorus in the Soil and in Plants

Phosphorus is needed for cell division, hence to promote root formation and growth, vigorous seedlings, flowering, crop maturity and seed production, and to improve winter hardiness in fall plantings. Phosphorus is important in fat, carbon, hydrogen and oxygen metabolism, in respiration, and in photosynthesis. It is stored in seeds and fruit.

Phosphorus binds easily with many other minerals in the soil, forming compounds that are not very soluble in water, therefore most of the phosphate in soils exists in solid form and phosphorus does not move freely with soil water. Although P is very mobile within plants, it is relatively immobile in soil and does not leach readily in normal rainfall or irrigation.

P is most available to plants between soil pH of 6 and 7.5, especially pH 6.5-6.8.

In neutral and alkaline soils P is mostly present as insoluble calcium phosphates. In acid soils below pH 5.5, most of the P is bound as iron phosphate or aluminum phosphate, compounds that further change gradually into very insoluble compounds not available to plants. If a soil test shows a pH that is far from neutral, with a slightly low P level, correct the pH and repeat the soil test before amending the P level.

In the soil water, P is only present in very small amounts, but when removed by plants, supplies are quickly replenished from the “active P pool” (P in solid compounds which is relatively easily released to the soil solution). The “fixed P pool” contains inorganic phosphate compounds that are very insoluble, and organic compounds that are resistant to mineralization by microorganisms in the soil. Although some slow conversion between the fixed P pool and the active P pool does occur in the soil, phosphate may remain for years without being available to plants and may have very little impact on soil fertility.

Since the movement of phosphates in soils is very limited, roots have to grow to the phosphorus—it will not move towards the plants. Manure contains soluble phosphate, organic phosphate, and inorganic phosphate compounds that are quite available. Water-soluble forms generally become insoluble very soon after application to the soil.

Phosphorus Deficiency

In cold soils less P is available from organic materials, because biological activity is required to release it and it runs slow when it’s cold. Also, roots cannot absorb P well from cool soils.  Early spring brassicas can show red or purplish colors (anthocyanin pigment) in the leaves, especially undersides, and the lower stems. Cell necrosis may follow. Root growth will be poor, plants may exhibit stunting and delayed maturity. Tomato plants may have yellow leaves, with purpling on the underside of leaves. They may exhibit reduced flowering and delayed maturity. To avoid P deficiency problems, wait until the soil is 60°F (15.5°C) before planting.

Effects of excess soil salt levels on crop foliage.
Photo Rose Ogutu, Horticulture Specialist, Delaware State University

Excess Phosphorus

The main symptom of excessive phosphorus in soil is stunted plant growth. High P interferes with N absorption. Also there may be symptoms of deficiencies of zinc, iron, cobalt or calcium, because the P has locked up these nutrients.  Zn deficiency shows as bleaching of plant tissue, Fe deficiency as yellowing between leaf veins. Co is involved in the process by which the plant stem grows, shoot tips elongate, and leaves expand. Ca deficiency produces blossom end rot of tomatoes.

Phosphorus inhibits the growth of mycorrhizae which help the plant absorb water and nutrients. Increased growth of non-mycorrhizal weeds such as velvetleaf, lambsquarters, pigweed and galinsoga can be sign of excess P, explained Klaas Martens at MOFGA’s 2009 Spring Growth Conference.

Aside from plant growth problems, the issues with having very high P levels in your soil include that if it reaches waterways it can accelerate eutrophication—the nutrient enrichment of surface water leading to problem algal growth. When an algal bloom dies, it decomposes, using up the oxygen in the water, so fish and other organisms die too. Phosphorus is a paradoxical element in that it is an essential nutrient, is not toxic itself and has low solubility, but can have damaging effects on water quality at quite low concentrations.  Because P is usually locked up, leaching of soluble P from soils is not normally a problem, but if soil particles are carried to a river or lake, P is contained in this sediment.

Mitigating High Phosphorus Levels

Ear of triticale.
Photo triticale-infos.eu

The quickest way to reduce excess soil P (which can take years!) is to stop any manure or compost application while continuing to grow crops that can be eaten or sold. One solution for vegetable growers may be to grow cover crops as forage crops, and graze or bale grass crops to sell off the farm as livestock feed. For example, triticale is very good at removing P from the soil and producing winter forage. The P removed ranges from 7–36 pounds/acre (7.8–40 kg/ha). The more P your soil has, then the higher the P level in triticale grown in that soil. Double cropping can remove P at twice the rate.

Vegetable growers do not have the problem of P accumulation to such a big degree as livestock farmers, nor do vegetable crops remove P at the rate forages do. See the New England Vegetable Management Guide Removal of Nutrients from the Soil for a table of Approximate Nutrient Removal by Selected Vegetable Crops. The best vegetable removers of P are celery (80 lbs P2O5/acre, 90 kg/ha), tomatoes (72 lbs, 81 kg), potatoes (65 lbs, 73 kg), sweet potatoes (60 lbs, 67 kg), peppers (52 lbs, 58 kg, fruits only), cucumbers (33–72 lbs, 37–81 kg), eggplant (56 lbs, 63 kg). Onions remove about 25 lbs (28 kg/ha) one-quarter of the P removed by alfalfa hay (104 lbs, 117 kg) In all cases, to achieve results this high, grow high yields and remove the vines too, although you can’t sell those! Beans and peas are in the 7–10 lbs (8–11 kg) range if just pods, 20 lbs (22 kg) with vines. P2O5 is 43.7% P.

Celery, the star of phosphorus-removing vegetable crops.
Photo Kathryn Simmons

Strategies to reduce the amount of P added each year include adjusting your compost use rates according to soil test P results. On low-P soil, use at rates to meet the soil needs for N or K, which will  increase P levels. If the soil P is high or optimum, use compost sufficient to just replenish P, and legume cover crops (or legume food crops) to supplement N. For very high or excess soil P, only use compost sparingly as a micro-organism inoculant, rather than a fertilizer, and  if  test reports show more than 40 lbs P per acre (45 kg/ha), consider using only soil amendments containing little or no P. If phosphorus levels are excessive, avoid using manure composts (high in phosphorus), and other fertilizers and amendments containing phosphorus. Add more carbon (“brown”) ingredients to compost you make on-farm.