Category: Cover crops

Book Review The Ecological Farm by Helen Atthowe

Front cover of The Ecological Farm

 The Ecological Farm: A Minimalist No-Till, No-Spray, Selective Weeding, Grow-Your-Own-Fertilizer System of Organic Agriculture, Helen Atthowe, Chelsea Green Publishing, 2023. 368 pages, $44.95.

 In this inspiring book, Helen Atthowe explains her 35 years of experience farming fruit and vegetables in Montana, California and Oregon. This book will appeal to all those (especially orchardists) who are fine-tuning their land management. I think beginners could find it over-whelming, unless they take it in rich small doses! This is definitely a book to dip into and come back to as needed. It provides a Big Picture of ecological farming, not a step-by-step How To.

Helen clearly pays exquisite attention to her farming, conducts research and share her knowledge with others. She operated an Organic orchard in California, together with her husband Carl Rosato, who very sadly died in a farm accident in 2019. Helen and Carl together pioneered ways to raise tree fruit with no pesticides at all. Helen has expertise in ecological weed, disease and pest management, minimal soil disturbance, and managing living mulches, providing soil fertility without manure-based compost, and cultivating habitat for beneficial species. There is lots to learn from this book.

The endorsements for The Ecological Farm are staggering: fifteen well-known ecological farmers (fourteen men and one woman, what’s with that?). Clearly, this work is held in high regard by many experts in the field. The love of farming goes beyond achieving high crop yields, embracing connection with the land and all its forms of life. Helen says “The process of creating farms and gardens opens my eyes to awe, attunes my ears to listening, and offers the gifts of curiosity, discovery and deep connection.”

The ecological approach in this book goes beyond organic, which in the wrong hands simply substitutes a different set of substances for the banned ones, and doesn’t look any deeper. Helen has measured the effects that her actions have had on her land and crops, and shares her results so that we too can grow nutrient-dense foods and leave the environment in a richer, more balanced state than we found it.

The book contains dozens of Helen’s own beautiful full-color photos of plants, pests, birds, fruit trees and vegetables in various combinations. There are prepared forms for monitoring problems and planning interventions. There is a Vegetable Crop Growing and Troubleshooting Guide, a section on Vegetable Crop Insect Pests and Interventions, one on vegetable crop diseases, and similar sections for tree fruit crops.

The first half of the book sets out ten empirical and practical Principles for Managing Ecological Relationships. As the name emphasizes, it’s about managing relationships, not managing crops for highest yields, regardless of what else happens. The connections that form healthy farming ecosystems require us to pay attention, and avoid outside inputs in favor of balancing what is happening on our own farm. There are some excellent charts of applying the ecological principles.

The Principles include creating above- and below-ground diversity; minimizing soil disturbance; maintaining growing roots year-round (living plants secrete 30-60% of the carbon they capture from the air during photosynthesis down into the soil); growing your own carbon; adding organic residues all season; focusing on carbon fertilizers; recycling rather than importing nutrients; fertilizing selectively; weeding selectively; and creating beneficial habitat as close to the crops as possible.

There are many ways to build soil organic matter without removing large quantities of inputs from someone else’s land (not sustainable or fair, as Helen remarks); many ways to build habitat for beneficial organisms; many actions that can steer plants, animals and fungi towards better balance, so that the soil microbial community will thrive and cycle nutrients continuously.

Helen tells that when she started farming, she behaved like a “nitrogen hoarder”, focused on maximizing the amount of nitrogen the soil had available, and topping it up with compost and cover crops if the soil held less than the requirement for the next crop. Her soil management went through a three-stage evolution: She started to view the abundance and diversity of active microbes as the important bit, and the nitrogen level as merely a sign of that activity. Next, she moved to consider the whole soil organic matter system, rather than the parts as separate features to measure. Thirdly, she researched soil carbon and realized that microbially-active carbon was essential fuel for the soil microbes, and deserved more attention.

Actual measurements showed that, contrary to careful calculations, her soil levels of nitrogen, phosphorus and potassium were becoming too high. Helen had been generously adding sheep manure and clover compost at 7-10 tons/acre (18-25 tons/ha). She changed to using mown clover as her main fertilizer, and learned to manage the carbon:nitrogen ratio, with the goal of achieving steady decomposition of organic residues and increased microbe populations and diversity. Simply adding more high-nitrogen material will not provide good crops! We need to build carbon in our soils, and optimize organic matter decomposition and nutrient cycling.

Helen discovered that the C:N ratio of mowed clover living mulch residue varied according to the time of year, being highest (least nitrogen, nodules not yet formed) in July and lowest (most nitrogen, clover flowering) in August and September. This affects nutrient availability and decomposition rate. Vegetable crops do best in Helen’s system if she tills once a year and regularly applies both high-C and low-C residues on the surface. The continuous organic surface residue supply is much better than an annual large dose. Timing when and how we apply organic residues influences their C:N ratio, and hence how we build up carbon in the soil.

Minimizing tillage is another way to build soil organic matter. Incorporated clover releases nitrate-nitrogen into the soil much more quickly than surface-applied cut clover. If your soil has an active and diverse microbial community, incorporating legume cover crops in spring can give a quick burst of nitrogen (for a few weeks), then a sustained regular release of more as it slowly decomposes. With no tillage there is a lag time. No-till does keep the fungal food webs unbroken, which has advantages. It is important to focus on the carbon fertilizers rather than fast-release nitrogen fertilizers. Since 2016, Helen has used only mowed living mulch as fertilizer for most crops, paying close attention to the timing of mowing. The vegetable plots also benefitted from the living mulch in the row middles growing over the bed after the food crop was finished.

I had to look up “row middles” to understand the methods better. With rows of fruit trees, row middles are the aisles between rows of trees. They can be planted in cover crops, which can be mowed and the cut material blown into the tree rows to act as mulch. The photos of vegetable production (other than her home garden) seem to show aisles wider than the beds, so that less than half of the land is in vegetables and more than half is in cover crops. This fits with the method of growing lots of cover crops as the main source of soil fertility. And with Helen’s method of always leaving half of the living mulch row middles unmowed to provide good habitat for beneficial insects. Over here on the East Coast, I am more used to intensive vegetable farms with narrow aisles between beds, perhaps because land is more expensive, perhaps because Bermuda grass is so invasive as to scare off anyone who might consider permanent paths. Jennie Love, a flower farmer in Philadelphia, uses Living Walkways. Hers are 21″ wide, mostly grass and weeds, and require mowing every single week. Helen’s are more focused on legumes, especially clovers.

To focus on a soil organic matter system driven by microbial activity, attention goes to C:N ratios, optimal decomposition speed and nutrient cycling of the cover crops, mulches and composts. As Helen admits, this can be overwhelming, so don’t change everything at once! As you gain experience growing your own fertilizers, you can cut back on imported fertilizers. Do provide a diversity of organic materials throughout the growing season. Having just one kind, all at once is, for the soil, like us eating a whole giant cheese pizza! Soil “indigestion” takes the form of an over-population of just a limited specific microbial community.

Decreasing nutrient inputs and increasing application of organic residues leads to an increase of mycorrhizal fungi. Including chipped woody compost increases the soil carbon. Adding cover crops increases not just the soil nitrogen but also the carbon as more microbial bodies are born, feed and die. Raw organic matter is to be avoided as it acts like an unmanageable surge that can burn plants (by releasing high levels of salts and toxic byproducts) and leach nutrients. In hot humid climates, it is best to aim for slow decomposition to balance the climate’s effect causing fast decomposition. Aim for ten weeks’ worth of nutrients, not more, and watch for foliar signals of nitrogen or phosphorus deficiency that last for more than 3 weeks – a sign that things are out of balance.

In early spring (if early harvest is a priority) you will need to provide easily available nutrients. The first couple of years after switching your focus to carbon, you may be frustrated by the slow rate of decomposition and the lower yields. It takes weeks longer for surface-applied plant matter to release its nutrients than it does for tilled-in plant matter. This requires patience, planning and also has financial implications. Wait 2-4 weeks after incorporating organic residues, or 4-6 weeks after spreading them on the surface, before planting. Animal manure is not essential for soil fertility. After all, animal manure is simply plant matter that has been partially digested. By applying the plant materials to the soil surface, the digestion is done by small soil animals. It’s not so different!

Letting living mulch grow tall in very wet or very hot weather will help dry or cool the soil, but don’t let the cover crop out-compete the food crops for water! Adding cut covers is also a way of adding to soil moisture. Helen is a fan of minimizing tillage, not of banning it.  Tillage decreases organic matter, microbial diversity and abundance, and disrupts the fungal chains. Strip tillage tills out narrow strips to plant into, from an existing sward of cover crops. Tillage incorporates organic residues, adds air, and stirs up a burst of biological activity, helps warm up spring soils, reduces weeds and breaks up compaction. These benefits can be put to use rather than scorned. “Practice tillage with intention” as Helen advises.

Likewise, compost can be useful when starting on poor land, or needing to address some other kind of imbalance. Don’t rule it out completely! There is plenty of information about making good compost here. Did you know the critical temperature for killing most weed seeds is 145˚F (63˚C)? This book also offers a recipe for a liquid fertilizer for “emergency use” on crops showing a nutrient deficiency.

Author Helen Atthowe.
Credit Cindy Haugen

I appreciate reading work by growers such as Helen, who have done the research and experimentation and responded to the science. An average of one page of footnotes per chapter backs up her claims. I’m not a fan of myths and “woo-woo” gardening. This book includes many useful charts and graphs, so you can see the facts. A four-year experiment started with a 50-year old grass, clover, alfalfa and weed pasture, was divided into two fertility treatments. The first was strip-tilled, with the mowed living mulch blown onto the 4′ (1.2 m) wide crop plots each spring. The second was similar, with the addition of 4″ (10 cm) of clover/grass/weed hay mulch in the late summer before the spring strip-tilling. The hay was cut from another field on the farm. Crop yields were economically sustainable in both plots all four years, and there were almost no insect or disease problems. Yields improved in the second and third years. Yields of some crops were higher with the hay addition – peppers and onions significantly; dry beans and cabbage slightly.

The information on choosing cover crops advises using mixes of crops with different C:N ratios, and including legumes whenever possible. This chapter includes recommendations on inoculants, cover crops for various soil types, and “biographies” of four perennials, 15 annuals and the biennial yellow sweet clover.

The book reminds (or informs) us that being able to stop using pest control sprays starts with building the soil, making it comfortable for soil microbes and creating habitat for natural enemies of the pests. The next step is growing healthy plants, by providing optimal conditions of light, temperature and water, and managing plant competition from weeds or over-thick sowing. After that, focus on the balance of nutrients in the soil, especially carbon.

Suppress pests, rather than focusing on killing them. Spraying insecticides, even organic ones, can disrupt balance and leave you inheriting the task of the creatures you killed. Killing all the prey starves the predators who were keeping the prey in check. Learn to intervene with the least possible impact. Tolerate non-threatening amounts of pest damage. Approach in this order: prevention, pest diagnosis, research, monitoring and ecological decision-making. Minimal-impact interventions include trapping and pest-specific microbial insecticides like Bt (which could require ten sprayings to achieve 98% damage-free Brussels sprouts); moderate-impact interventions include broader-spectrum microbials and materials like soap, horticultural oils and minerals; heaviest-impact interventions (those likely to injure non-targets) include using neem oil, pyrethrin, pyrethrum powder and spinosad.

Designing and maintaining a disease-suppressive ecosystem is the title of the section that focuses on preventing diseases. Crop rotations and diversity of crops and other plants are at the top of the list.

Plant competition is the description of the effect of weeds and over-thick planting. We are encouraged to focus on the weeds most likely to cause problems leaving those that can peacefully co-exist with the crop. Knowing and understanding weed ecology is important: when and where does this weed do best? How can you make your vegetable gardens less comfortable for the weed?

Perennial weeds that spread underground need good attention. Helen deals with quack grass, which takes about four years to become a serious invasion problem, when three passes with the tiller 7-10 days apart in spring are needed. I’ve lived with quack grass (couch grass), a cool-weather invasive. It’s a challenge, but I do think the warm-weather Bermuda grass (wire grass) is worse. Tilling also deals with that.

Crop rotations, especially of crops that grow in different seasons, underground crops that need soil disturbance to harvest them, and crops that rapidly cover the soil, are a big help. Helen recommends growing a full-season perennial cover crop on 25-50% of your garden beds or farm area in production each year to break annual weed cycles.

Some cover crops, including cereal rye, hairy vetch, red clover, sunflowers and mustards all exude allellopathic compounds that inhibit germination of nearby seeds (weeds and crops). Often incorporating the cover crop in the soil works better than chop-and-drop, as buried plants decompose without much air, giving a stronger effect. Also tilling reduces the immediate competition from weeds. Tillage can increase yields even if you believe no-till is best! It’s a trade-off. Tillage reduces soil health. Perhaps the sweet spot is minimal tillage, such as strip tillage. Landscape fabric (reused for ten years) offers another method of weed management.

Part Two of the book (approximately half of the pages) covers an ecological approach to crop management and troubleshooting. I didn’t take as many notes of that. After the introduction to some techniques like interplanting, succession planting, making your own microbially-amended seed growing mix, and using season extension tools, the book focuses on thirty popular crops, with tips on crop management, pests and problems.

A tidbit I learned with spinach is that fall-sown plants that reach the two-true-leaf stage before winter will resume growth in late winter. I also learned that the western striped cucumber beetle has a reddish thorax, making it look more like our striped pigweed flea beetle without such sturdy leg muscles.

The crop management sections include soil and fertility needs and special ecological preferences. The problems sections describe symptoms first, then causes, then resistant cultivars and other strategies for avoiding that problem in future. A valuable reference, and good winter browsing when reviewing the season past and preparing for the coming year. The index covers a substantial 18 pages, in three columns, promising to be comprehensive!

Helen Atthowe still acts as advisor to her previous farm, Woodleaf Farm in eastern Oregon, and is a farm consultant in the US and internationally. I notice that Helen is a speaker at the November 2023 Carolina Farm Stewardships Sustainable Farming Conference.

Helen Atthowe, November 2017.
Photo from Veganic World

Planting winter hoophouse crops

Our first hoophouse radishes germinated three days after sowing. We sowed Cherry Belle and White Icicle. We would have sowed Easter Egg if we’d had enough seed left after the outdoor fall sowings.
Photo Pam Dawling

We’ve already prepared our first bed in the hoophouse and sowed our first few crops (spinach, radishes, scallions, tatsoi, Bulls Blood beets and cress). We spread the bed prep out over 5 days and the sowings over 2 days. I’ve written lots about our fall hoophouse planting, so I’ll give you links, mention a few updates and stick to photos otherwise.

Mid-October photo of September-sown tatsoi and August-sown Tokyo bekana. Fast-growing crops make good use of small windows of time.
Photo Pam Dawling
  • Hoophouse Winter Schedule Tweaks and Improvements (pack more crops in, get higher yields, reduce or spread the workload). One change we made was to sow some early catch crops in areas that weren’t needed for all-winter crops until later. We mostly used tatsoi and Tokyo bekana, both fast–growing leafy greens. We intended to grow some early beets too, but the seed didn’t germinate. A new crop last winter was cress, Creasy Greens Upland Cress and Belle Isle Upland Cress from Southern Exposure. They take 50 days to maturity (in spring). We had two good intentions we did not manage to follow through on. One was to let some of the cress flower, to feed beneficial insects. And I think we got too impatient. The other was to notice which one of the two kinds we prefer and just grow that one. We didn’t manage to keep good enough records on that, so this winter we are obliged to repeat the experiment, with more good intentions!
Belle Isle Upland Cress from Southern Exposure Seed Exchange
  • Using all the space in the winter hoophouse (filler crops for random spaces, fast-growing catch crops, radish sowing dates for seamless harvests.)
  • Fall hoophouse bed prep and shadecloth removal (packing away the giant piece of shadecloth until May, spreading compost, broadforking and raking the beds, direct sowing the first bed, sowing seeds in an outdoor nursery bed to transplant into the hoophouse a few weeks later). This post includes a step-by-step guide to hoophouse fall bed prep. Our soil is improving each year, becoming easier to broadfork and rake. That counters the aging process of our human bodies! One change we made last year was to measure and pin down the drip tapes 12” (30 cm) apart, and use the drip tape as a guide to making furrows (drills). This is easier than using the row marker rake, as we used to do.

    Our hoophouse with shadecloth for growing summer crops. Photo Pam Dawling. We have now sewed the two pieces together, to avoid the gaping hot spot in the middle!
  • Hoophouse fall bed prep (includes an appreciation of spiders and a video of spider “ballooning”)
  • Sowing hoophouse winter crops (more details on bed prep tools and techniques, including the row marker rake if you want to use that, and links to posts about winter lettuce varieties we used in 2017/2018.)
  • Planning and Growing Winter Hoophouse Vegetables (hoophouse crop map, many links to other posts including a video and three slideshows, crop rotations, choosing winter hoophouse crops, posts about specific crops (with all the details), back up plans in case something goes wrong, and harvesting.)

    Mid-October emergency back-up seedlings for the hoophouse.
    Photo Pam Dawling. We needed to compensate for poor germination that year.
  • Preparing your hoophouse for fall and winter (includes one of my slideshows, and a more detailed discussion of lettuce types and sowing dates, information about salt build-up and our wash-down strategy in a 3-slide mini slide show, when we close and open the doors and windows, and a Be-Prepared Winter Kit list)
  • Planning winter hoophouse crops – our step-by-step process for hoophouse crop planning.

    Spinach seedlings (from pre-sprouted seed) emerged on the third day after sowing. here they are on day 4. Photo Pam Dawling
  • Winter hoophouse growing (includes a round-up of earlier posts, and a discussion about the value of crop rotation in the hoophouse, and a list of 20 benefits of having a hoophouse.)
  • Spinach variety trial conclusions This year we are growing Acadia.  Johnny’s do not recommend this variety for late fall or winter sowing, but it did very well in our hoophouse, sown in September, October, November and January.
  • September in the hoophouse: sowing spinach 
Two jars of sprouted spinach seeds and grits to prevent the damp seeds clumping. presprouting spinach seeds for a week in a fridge gets round the impossibility of getting spinach to germinate in hoophouse soil at 80F (27C) as it is September 11.
Photo Pam Dawling
One side of our hoophouse on Sept 10. Three beds with cover crops of buckwheat and sunnhemp (which got bitten down at a young age by Something), and one bed under solarizing plastic in hopes of killing nematodes. Photo Pam Dawling
Zipper spider on the pepper plants in our hoophouse September 10.
Photo Pam Dawling

Cover Crops for September: wheat and crimson clover

Crimson clover is a beautiful and useful cover crop.
Photo Kathryn Simmons

Note: the day after I posted this I found I was mistaken in believing barley to die at a warmer temperature than oats, so I’ve edited it.

Focus Cover Crops for September: Winter Wheat and Crimson Clover

In August I wrote about cover crops such as millets, southern peas, buckwheat which are frost-killed. If it’s still too early to sow your winter cover crops, sow summer cover crops. Before I get to the wheat and crimson clover, I’ll mention some other useful seasonal cover crops.

Winter-killed, not frost-killed, cover crops

There are also cover crops that are not frost-killed, but die later in the winter, at colder temperatures, such as oats and barley. Only sow oats or barley if you are sure you can get them turned under or killed by cold winter weather before they seed. They will not mow-kill, so if the weather doesn’t kill them, you will have to turn them under. Be careful buying feed-grade seeds (rather than Organic seed-grade), as they can contain weed seeds including GMO canola.

Late corn undersown with oats, now mowed high, and the sweet potato patch now sown in winter wheat and crimson clover.
Credit Ezra Freeman

If the area is clear of vegetable crops by 40-60 days before frost, sow oats to winter-kill. If possible add a legume (soy and spring peas are easy, and will be killed by the frost, so they won’t complicate food crops next year). For us with a first frost date of October 14-20, the cut-off date for oats is September 7, or September 15 if we really push it. Sowing too late means you don’t get enough growth in the fall, and the soil is not adequately protected from erosion or from weed growth.

We sow oats after growing early sweet corn, spring broccoli, spring-planted potatoes, cabbage, kale, or early season spinach, lettuce, beets, carrots. Spring oats die after three nights at 20°F (-7°C), or a single plummet to 6°F (-17°C), leaving the plot quick to prepare for early crops next year. Winter oats are hardier, but my goal with growing oats is for them to die in winter. After oats or other winter-killed cover crop, we like to plant our early spring food crops, peas, cabbage, broccoli, carrots, March-planted potatoes, spinach and the first sweet corn.

Don’t let your cover crop barley go to seed! Photo USDA

Fall-sown barley (Hordeum vulgare), grows even faster than oats, but not as quickly as winter rye, and it won’t die as early in the winter as oats. Barley dies at 17°F (-8°C). It usually will die in Zone 7 and colder regions. The dead barley residue protects the soil through the winter, and dries into what Barbara Pleasant calls “a plant-through mulch” in spring in cold zones.

See Planning Winter Cover Crops, a post that includes my Short Simple Guide to Winter Cover Crops and my slideshow Cover Crops for Vegetable Growers. Oats, barley, wheat and rye sown too early can head up and seed before you get to winter, making them less useful, and more of a weed problem.

Winter-hardy grass cover crops to sow in September

It is too late for us to usefully sow cover crops that are not frost-hardy, as they won’t make enough growth before getting killed.

Winter rye and winter wheat are two grass cover crops that can be sown in the mid-Atlantic in September. Wheat is easier to incorporate than rye and has less of an allelopathic effect on small seeds, the inhibition of germination that lasts three weeks after rye is turned under. It’s true wheat doesn’t produce as much biomass as rye, so there’s the tradeoff. We sow wheat if the area is ready for cover crops 20-40 days before frost. This allows us to make faster use of those plots in the spring, compared to plots sown to rye.

Winter wheat
Photo USDA

For us wheat is a good, trouble-free winter cover crop. Winter wheat prevents erosion, suppresses weeds, scavenges excess nutrients, adds organic matter, encourages helpful soil microorganisms, and the fine root system improves the tilth. It is less likely than barley or rye to become a weed; easier to kill than barley or rye; cheaper than rye; easier to manage in spring than rye (less bulk, slower to go to seed); tolerates poorly drained, heavier soils better than barley or oats. If you have leftover seed, wheat can be sown in spring – it will not head up, but “wimps out” when the weather gets hot.

The challenges of wheat are that it does not have good tolerance of flooding, and is a little more susceptible than rye or oats to insects and disease.

Secondary cover crops in September:  Include legumes where possible

With careful planning, you can grow next year’s fertilizer for your later spring-planted vegetables! Legumes grow nitrogen-fixing bacteria on their roots, which can feed the next food crop. You may need to buy a suitable inoculant if you are introducing a new legume species. You may decide to inoculate anyway, for insurance, even if that type of legume is already somewhere in your garden. Before sowing the legume seed, dampen it, sprinkle the inoculant over the seed at a “pepper on your dinner” rate, and stir it in. Then sow the seed. Be sure not to make the seed wetter than slightly damp, or you’ll need to spread it out to dry a bit before you sow.

Two other key parts of being successful are to sow the legume early enough to establish before winter halts growth, and to plan not to need that plot next year until flowering time for that legume. At flowering time, legumes have the maximum amount of the nitrogen nodules they will have. Don’t let the legume flowers set seed, or they may become a weed problem. Take notes on when various legumes flower. If you have a legume that doesn’t reach flowering, it’s not the end of the world, you just get less nitrogen for your money, and won’t be able to supply all the N needs of the following food crop.

September (40-60 days before frost) is a good time to sow clovers here, provided you can supply enough overhead irrigation. They will make some growth in our climate before winter, and then a lot more once spring arrives.

Crimson clover cover crop with bumblebees.
Photo Bridget Aleshire

Crimson clover is a good September choice, if you won’t need to prepare the area before it flowers (in central Virginia 4/16-5/2, most usually around 4/20).

For a cover crop to survive the winter, sow winter wheat with Austrian winter peas, crimson clover, hairy vetch, red clover, white clover or fava beans. Hairy vetch takes a few weeks longer than crimson clover to reach flowering. Which you choose will depend what you want to grow there next spring and when you need to plant it.

Clover for green fallow in early September

See August’s post for info on planting a Green fallow plot (Full year cover crops)

Time is running out on this for us, but you may still have enough warm weather where you are. A green fallow crop (all-year cover crop) will replenish the soil and reduce annual weeds for the following year. In late August, or early September, four weeks after transplanting your fall brassicas, especially cabbage and broccoli, but also kale and collards, broadcast a mix of clovers: 1 oz (30 g) Crimson clover, 1 oz (30 g) Ladino white clover and 2 oz (60 g) Medium red clover per 100 sq ft (9 m2). Crimson clover is a winter annual and will be the biggest and the first to flower, in April. Medium red clover is a biennial and will be the next to flower. White clover is perennial and will take over the plot as the others subside. Be sure to get the medium red clover, not the Mammoth kind that dies when mowed. Likewise, for maximum benefit, get the tall Ladino white clover, not the low-growing “wild” type. In March, mow down the old brassica stumps and let the clovers flourish. You will be mowing this patch about once a month from March to October next year to prevent the crimson clover and the annual weeds from seeding.

Cover crops to sow soon after your first frost date

I’ll say more about this next month, and because I want this website to be useful to a geographically wide range of growers, I’m including a preview here. If the area is ready for cover crops up to 10 days past the frost date, sow winter wheat or winter rye with hairy vetch or Austrian winter peas. Winter rye is hardier than any other cover crop and can take later planting dates. But it is a bit harder than wheat to incorporate in the spring. Sow winter rye from 14 days before to 28 days after first fall frost. See Working with the time you have left in the Summer Cover Crops post. Austrian winter peas can be sown later than other legumes, it’s too late for clovers.

My book Sustainable Market Farming has a chapter on cover crops and many pages of charts about particular options.

The book Managing Cover Crops Profitably (third edition) from the Sustainable Agriculture Research & Education Program (SARE), is the best book I know on the subject. You buy the book for $19 or download it as a free PDF from SARE.

Cover crops for August: Oats and Barley

From the USDA Barley Plant Guide

Note: I edited this post in September when I found I was mistaken in believing barley was less cold-hardy than oats.

Focus Cover Crops for August: Oats, barley and other winter-killed cover crops

In August we are looking ahead, thinking about how our cover crops will be impacted by future cold weather. In July I wrote about hot weather grass cover crops, including Sorghum-Sudan hybrid (Sudex), and the millets, which are not frost-hardy.

German/Foxtail and Japanese millets are day-length sensitive. Growth is considerably less if they are sown after the summer solstice, so they are likely to be of limited use as cover crops once we reach August.

Browntop Millet could be useful in August in the mid-Atlantic. Proso/Broomcorn Millet I’m not so sure about. Pearl/ Cattail Millet is not day-length sensitive. To winter-kill and avoid seed formation, sow 60-85 days before your expected first frost.

See Working with the time you have left in the post Cover Crops in Summer. See No-Till summer cover crops in that same post (Soy, southern peas, foxtail millet). Also there, see Five Easy Summer Cover Crops that Die with the Frost (buckwheat, sorghum-sudan grass, soybeans, southern peas and sunn hemp.)

Buckwheat cover crop in flower.
Photo Pam Dawling

Buckwheat can be sown up to 28 days before the first frost.  See my article about buckwheat. Soybeans can be sown up to 45 days before frost. A mix of sunn hemp, soybeans or southern peas and other frost-tender cover crops can be grown during August (60-80 days before frost) before planting garlic in mid-fall. This method will work more easily if you mow the cover crop around your frost date, so that it is easier to make furrows in the soil. Forage radish, lab-lab beans or bell beans sown now will die back and leave almost bare soil. This is a boon for the very earliest spring transplants or sowings.

Or, instead of sowing a cover crop now, you could sow a fast-growing vegetable crop. Kale, spinach, Tokyo bekana, radishes, chard, lots of salad crops, senposai, mizuna, tatsoi, or land cress. Try Eat-All Greens, an idea form Carol Deppe. Patches of carefully chosen cooking greens are sown in a small patch. When it reaches 12″ (30 cm) tall, Carol cuts the top 9″ (23 cm) off for cooking, leaving the tough-stemmed lower part, perhaps for a second cut, or to return to the soil.

Twin Oaks Eat-All Greens on October 19.
Photo Bridget Aleshire

Winter-killed, not frost-killed, cover crops

In August, we can sow winter cover crops to be winter-killed for easy soil cultivation before early spring vegetables. Oats and barley are in this category. Oats will be killed by three nights of 20°F (-7°C) or a single night of  6°F (-14°C). Sow oats 5-8 weeks before your average first frost to get good size plants before they get winter-killed. We sow in late August and early September in Zone 7a. See Cover Cropping Your Garden by Chris Blanchard in 2002:

“Inexpensive and easy to grow, oats are a standard early fall cover crop in the northern and middle sections of North America.  A quick-growing, non-spreading grass, oats will reliably die in Hardiness Zone 6 and colder, and often in zone 7.”

It used to be nine years out of ten, here in Louisa County, VA, but our climate is shifting to be too warm in winter to reliably kill oats. This past winter (2022/2023) oats did not die. They were cold-damaged, and set back, but definitely not dead.

We can no longer rely on our winter cover crop oats getting winter-killed. March photo by Pam Dawling

Fall-sown Barley (Hordeum vulgare), grows even faster than oats, although not as fast as winter rye, and it won’t die as early in the winter as oats. Barley dies at 17°F (-8°C). It usually will die in Zone 7 and colder regions. The dead barley residue protects the soil through the winter, and dries into what Barbara Pleasant calls “a plant-through mulch” in spring in cold zones.

See Planning Winter Cover Crops. If the area has been fully harvested of food crops by 60-80 days before frost, sow a frost-killed cover crop or even a fast-growing food crop.  In central Virginia, it’s a mistake to sow rye as early as August, as it can set seed.

Winter-hardy cover crops to sow in August

Not all winter cover crops can be sown as early as August in the mid-Atlantic. Don’t sow winter rye, or it may head up before winter and drop seeds. Only sow oats or barley if you are sure you can get them turned under or killed by cold winter weather before they seed. They will not mow-kill. Be careful buying feed-grade seeds (rather than seed-grade), as they can contain weed seeds including GMO canola.

Clovers can be sown in August (provided you can supply enough overhead irrigation). September is a better time to sow clovers here, if you are sowing them in bare ground. They will make some growth in our climate before winter, and then a lot more once spring arrives.

Secondary Cover Crops in August: Undersowing for more cover crops

  • Choose vigorous food crops, but cover crops that are only moderately vigorous.
  • Timing is critical: Sow the cover crop late enough to minimize competition with the food crop, but early enough so it gets enough light to grow enough to endure foot traffic when the food crop is harvested. Often the best time is at the last cultivation.
  • The leaf canopy of the food crop should not yet be closed. With vining food crops, sow the cover crop before the vines run.
  • Ensure a good seedbed and a high seeding rate.
  • Irrigate sufficiently. The food crop will have good roots by then, but the cover crop seed will be just below the surface and will need some help to germinate.

 Green fallow (Full year cover crops)

Fall broccoli undersown with a mixed clover winter cover crop.
Photo Nina Gentle.
  • Our main use of clovers is to undersow fall brassicas such as broccoli and cabbage, with a mix of Crimson clover, white clover and medium red clover in August, to form a green fallow crop (all-year cover crop) for the following year, replenishing the soil and reducing annual weeds.
  • 2 weeks after transplanting the brassicas (August), we hoe and till between the rows, or wheelhoe.
  • We repeat at 4 weeks after transplanting, and broadcast a mix of clovers (late August-early September): 1 oz (30 g) Crimson clover, 1 oz (30 g) Ladino white clover and 2 oz (60 g) Medium red clover per 100 sq ft (9 m2)
  • In March, we bush hog the old brassica stumps and let the clovers flourish, mowing once a month to prevent the crimson clover and the annual weeds from seeding.

See my Mother Earth News post: Late summer and fall intercropping of cover crops in vegetable crops, aka undersowing.

If you have difficulty getting even coverage when broadcasting clovers or other cover crop seeds, try seeding half the crop walking in one direction, and then seed perpendicularly across your original path

In mid-August, we undersow our last sweet corn planting with oats and soybeans, as the winter cover crop, which winter-kills, leaving a plot that is easily worked up next spring. Our 6th sweet corn is sown 7/16. 4 weeks after seeding, we cultivate and sow oats and soy. In mid-March we follow with our spring potatoes. Both oats and soybeans have some tolerance for shade and for foot traffic (harvesting corn!).

Late season sweet corn undersown with oats and soy
Photo Kathryn Simmons

Sweet corn can be undersown with clover rather than soy or oats in some climates. We tried clover but found it harder to germinate in hot weather, and harder to keep the tiny seed damp. Buckwheat can be undersown in corn as a short term summer cover, but according to Sue Ellen Johnson, (co-editor of Crop Rotation On Organic Farms: a planning manual, it grows rather straggly in the shade of the corn. Soy has the advantages of tolerating shade as well as foot traffic.

We tried an idea from NY State, or undersowing winter squash with buckwheat and tilling it under just before the vines run (that was June), but here in the south, the vines ran too fast. We ended up having to wade in among the vines to pull up the buckwheat by hand!

You can drill cover crop seeds using a push seeder. See VABF Using Manually-Operated Seeders for Precision Cover Crop Plantings on the Small Farm. Don’t worry if the seed ends up deeper than ideal. It will still germinate. On a small scale, you can sow by hand, either broadcasting and raking in, or in close rows using a hoe, as if sowing

Cover Crop Planning

My book Sustainable Market Farming has a chapter on cover crops and 9 pages of charts about particular options.

The book Managing Cover Crops Profitably (third edition) from the Sustainable Agriculture Research & Education Program (SARE), is the best book I know on the subject. You buy the book for $19 or download it as a free PDF from SARE.

Cover Crops for July: Millet and Sorghum-Sundangrass

Focus Cover Crops for July:                     Millet and Sorghum-Sudangrass (Sudex)

In July we are very much looking for cover crops that will grow in hot weather. Last month I wrote about sunn hemp, with some notes about other hot weather legumes. This month we are turning our attention to good hot weather grass cover crops. Warm weather grass cover crops we use include Sorghum-Sudan hybrid (Sudex), and the millets.

Next month I will discuss winter-killed winter cover crops before early spring vegetables and undersowing winter-hardy cover crops in standing vegetable crops.

Also see my post Cover Crops in Summer for much more information, including  making space, sowing small spaces and finding time for the work.

Don’t sow a winter cover crop yet. If sown too early, oats head up in the fall and even drop seed. Only sow oats or barley in July in southern regions if you are sure you can get them turned under before they seed. They will not mow-kill.

Cover crop seeds are usually easier to find and cheaper at a local feed store, rather than online. Also you’re likely to find a regionally-adapted variety. But, of course, you may not find USDA Organic seed there. Be careful buying feed-grade seeds (rather than seed-grade), as they can contain weed seeds including GMO canola.

Variation in spring field corn root development at harvest following various summer cover crops. Preceding cover crop from left to right: sunn hemp (residues mulched in), pearl millet without fertilizer, sorghum-sudangrass, corn, pearl millet with fertilizer, and sunn hemp (residues harvested). Credit: Z. J. Grabau, UF/IFAS

Types of millet

Millet has good insect resistance and is relatively free of diseases. Read the descriptions below and especially the final height, the days to maturity and whether or not it mow-kills at any stage. See Working with the time you have left in the post Cover Crops in Summer. Avoid the trouble I had battling pearl millet with small walk-behind equipment, having to mow it frequently to keep it manageable.

German/Foxtail Millet

Foxtail millet seed heads.
Photo Eden Brothers Seed Supply

Setaria italic, 3-4’ (1-1.3 m) Fast growing annual (60-70 days). 75-90 days to seed formation. Not frost hardy. Mow-kills or roll-kills reliably after heading.

Sowing date: Needs warm soil. From 2 weeks after last frost onwards. Growth is considerably less if sown after summer solstice – day-length sensitive.

Sowing rate (US): Drilled:20 #/ac, Broadcast:30 #/ac, B:1-1.5 oz/100 ft2

Sowing rate (metric): D:22 kg/ha, B:34 kg/ha, B:3-4.5 gm/m2,

Uses and Cautions: Can be followed by late summer and fall crops. Fairly well-behaved – unlikely to become a weed. Easier than most other millets to incorporate.

Notes: Small seeds need good seedbed and few weed seeds. Fairly drought-tolerant once established. Shallow roots.


Japanese Millet

Japanese Millet
Photo Hancock Seed Company

Echinochloa esculenta 3-5’ (1-1.6 m). Fast growing annual, 45 days. Not frost hardy. Foxtail type, grown more in the north. Cannot mow-kill or roll-kill reliably.

Sowing date: From corn planting date. May and early June are best in the mid-Atlantic. Can be sown until early July, but growth is considerably less if planted after summer solstice because it is day-length sensitive.

Sowing rate (US): D:15-25 #/ac, B:35 #/ac, In mix with soy:54 # soy:12 # millet/ac, B:2 oz/100 ft2

Sowing rate (metric): D:17-28 kg/ha, B:40 kg/ha, In mix with soy:60 kg soy:14 kg millet/ha, B:6 gm/m2

Uses and Cautions: Can be followed by summer and fall vegetable crops.

Notes: For best re-growth, mow at 60 days when 3’ (1m) tall, and before heading. Cut to 3-8” (8-20 cm) and repeat every 40 days after that. If cut after heading, it will flower again in 2-4 weeks on short stems and set seed. Tolerates drought and wet soils, including cold wet soils.

Browntop Millet

Urochloa ramosa (L.) Nguyen. 2-5’ (0.6-1.5 m). 50-60 days. Cannot mow-kill. Foxtail type, grown more in the south.

Sowing date if last frost is 4/30, first frost 10/14. May – August

Sowing rate (US): D:20-30#/ac, B:30-40 #/ac, B:3 oz/100 ft2

Sowing rate (metric): D:22-34 kg/ha, B:34-45 kg/ha, B:9 gm/m2

Notes: Tolerant of acidic soils, low fertility and flooding.

Proso/Broomcorn Millet

Jean Hediger grows Proso millet on her Nunn, Colorado farm
Photography courtesy of Jean Hediger

Panicum miliaceum, More than 5’ (1.6 m) 60-90 days to maturity.

Sowing: Optimum soil temperature ranges from 55°F-65°F (13°C-18°C)

Sowing rate (US): D:20 #/ac, B:30 #/ac

Sowing rate (metric): D:22 kg/ha, B:34 kg/ha

Uses and Cautions: Can be followed by summer and fall crops. Seed heads may shatter once the topmost seeds are mature.

Notes: Cut after 60 days before it gets tough. A much finer textured grass than Pearl or Japanese millets. Makes a good mulch.

Pearl/ Cattail Millet

Pearl Millet
Photo USDA i7wiafe6

Pennisetum glaucum or P. Americanum, 5-10’ (1.6-3.2 m) Fast growing, 60-75 days. Not frost hardy. To winter-kill and avoid seed formation, sow 60-85 days before expected frost.

Sowing date: From corn-planting date until 60 days before fall frost. Soil temperatures of 75-90°F (24-35°C) are ideal.

Sowing rate (US): D:15#/ac in 18” rows, B:25-40 #/ac, B:1-1.5 oz/100 ft2

Sowing rate (metric): in 45 cm rows, B:28-44 kg/ha, B:3-4.5 gm/m2

Uses and Cautions: Can be followed by summer and fall crops. Or by early spring crops, if winter-killed.

Notes: Does OK in poor soils. Does not tolerate water-logging. Excellent biomass, even if sown in late summer, as it is not day-length sensitive. Mow before heading for fast regrowth. After heading it is fairly easy to mow-kill, although not as easy as German and Japanese millets.

How to broadcast seeds

To broadcast seeds, you can buy a shoulder-bag with a hand-crank that shoots out the seeds. Or you can develop a manual technique: take a handful of seeds from a bag or bucket you carry with you. Fling the seed confidently in front of your body in a wide fanning motion. Use a loose touch, don’t grip the seeds! Aim for about two seeds per square inch—but don’t worry if you don’t hit that goal. Broadcasting seeds is an art, and the exact density and pattern doesn’t matter.

While you are learning, try seeding half the crop walking in one direction, and then repeat at 90˚ to your original direction. After seeding, rake the seeds in, aiming to bury most of them ½-1” (1-2 cm) below the surface, but don’t sweat the details. Next, especially if water is in short supply, roll or tamp the soil so that the seed is in good contact with the soil, which will help it get the water it needs rather than drying out in an air pocket. Then irrigate with rain, a hose or a sprinkler to keep the soil moist until germination. Drip irrigation won’t do it.

EarthWay push seeder.
Photo from EarthWay

Alternatively drill the seed by hand with a hoe, or using a seeder. See VABF Using Manually-Operated Seeders for Precision Cover Crop Plantings on the Small Farm. Don’t worry if the seed ends up deeper than ideal. It will still germinate.

Sowing millet in mixes

See No-Till summer cover crops. A mix of soybeans or southern peas and foxtail millet can be grown during the summer and mow-killed (after heading), before planting in the fall. Garlic perhaps?

Mixes can generally be sown at a depth of 1” (2.5 cm), regardless of seed size. Major ingredients for a summer mix could include soy, southern peas and buckwheat. Lesser ingredients could include pearl millet, proso millet, radish, turnips, sunflowers and sunn hemp.

  • When legumes and grasses are mixed, sow on the date for the grass.
  • When 2 grasses are mixed, reduce the seeding rate of each by a third.
  • Do not reduce the seeding rate of legumes in mixtures.

———————————————————

Taking down large cover crops

Don’t grow sorghum-sudangrass unless you have tractor-mounted equipment. Even some of the millets are quite large. Before planting, have a plan for how you will terminate the cover crop. You don’t want to delay getting your fall vegetable crops established.

On a small scale, most gardeners mow cover crops down, or pull them, and use for mulch (chop-and-drop) or compost. It may be that composting produces a more balanced soil amendment compared to incorporating raw residues directly into the soil.

If you avoid incorporating the cover crop, you can plant the next crop right away. Some cover crops (such as Sorghum-Sudangrass) produce allelopathic substances that can temporarily inhibit the germination of seeds, meaning you have to wait three weeks to plant.

If cover crop residues are left on the surface rather than incorporated, the rate of decomposition is slowed. Some N is lost to the air (denitrification), but the increased organic matter can increase the diversity of micro-organisms at the surface. 80% of the carbon from cover crops is below the top 8” (20 cm), where almost all soil data are collected. Remember the value of the roots!

———————————————————– 

Sorghum-Sudangrass

Sorghum-Sudangrass hybrid/Sudex grows 5’-12’ (1.5-3.6 m) tall in 60-70 days and produces an impressive amount of biomass.

  • It cannot be mow-killed. It is not frost hardy.
  • Sow ½-1 ½” (1-4 cm) deep (less deep than corn). Plant seeds 1.5” (4 cm) apart in rows 8” (20 cm) apart (for best weed-suppression), or up to 36-42” (90-110 cm) apart.
  • Sowing date: From 2 weeks after corn-planting date (needs warm soil) and anytime onward until six weeks before frost. In zone 7, mid-May to late August. Plant earlier at your own risk – I think we’ve had some success despite the warnings.
  • Sowing rate (US): Drilled:25-40 #/ac, less if rows 36-42” apart. Broadcast:40-50#/ac. Broadcast:2 oz/100 ft2
  • Sowing rate (metric): Drilled:28-56 kg/ha, less if rows 90-110 cm apart Broadcast:45-56 kg/ha, Broadcast:6 gm/m2
  • Sorghum-sudangrass will smother weed competition, and make big improvements to the soil texture and the levels of organic matter.
  • Fast growing, deep rooting.
  • Good in preparation for new strawberry beds.
  • Suppresses root-knot nematodes, soybean cyst nematode and annual ryegrass.
  • After it’s established, sorghum-sudangrass is highly drought-resistant and thrives in summer heat

      • Sorghum-sudan cover crop after mowing to encourage regrowth.
      Photo Kathryn Simmons

    When the sorghum-sudangrass reaches 4’ (1.2 m) tall, cut it down to 6”-12” (15-30 cm) to encourage regrowth and more, deeper, root growth that will loosen compacted soil.

  • The cut tops make a good long-lasting mulch, in place, or to haul elsewhere.
  • Good ahead of fall crops if given 8-10 weeks of growth.
  • Winter-killed Sorghum-Sudan can be followed by early spring crops.
  • Sorghum-sudangrass roots exude allelopathic compounds that suppress pest nematodes and inhibit small seeds (weeds and crops) from germinating and even inhibit the growth of tomatoes, lettuce, and broccoli.
  • Wait at least 6 weeks after incorporating sorghum-sudangrass before planting a susceptible crop in the same spot.
  • Does well in mixes with buckwheat, soy, and/or viney legumes.
  • Can mix 10 # with 50 # southern peas/ac (11 kg with 56 kg southern peas /ha).
  • Sunn hemp and sorghum-sudangrass grow well mixed together. Try a 50:50 mix to start with. This mixture can increase overall biomass and the diversity benefits soil microorganisms and therefore nutrient cycling.
  • Be careful if feeding to livestock. Read up about prussic acid poisoning from this cover crop. Young plants (less than 24” (60 cm) tall) and those stressed by drought or killed by frost, can cause prussic acid poisoning. Ducks, geese and goats enjoy the forage.
  • It’s undeniable that Sorghum-Sudangrass can be hard to incorporate once tall, unless you have tractor-based equipment. It is too massive to tackle with small mowers or weed whips.

———————————————————–

Secondary Cover Crops in July

In July, legumes such as sunn hemp, soybeans, southern peas, and Partridge pea are good legumes to consider. See June’s post for more about those and also Senna Ligustrina a native perennial legume. Another option is summer, if you have a weedy area or suffer with nematodes or foliar fungal diseases, is solarization.

Solarization

Solarizing with clear plastic. Photo Pam Dawling

Solarization uses clear plastic (old hoophouse plastic is ideal) to kill pests, diseases and weed seeds near the surface of the soil by covering the soil for six weeks or more in hot weather.

If you are solarizing to kill weeds, you can see when they are dead. Bryan O’Hara poked a thermometer probe through solarization plastic and found a 50F degree (28C) difference between the outside air and the soil immediately under the plastic; a 10F (6C) difference at 1″ (2.5 cm) deep and little temperature gain lower than that. Solarization does not kill all the soil life below the surface level!

Extension offers Solarization and Tarping for Weed Management on Organic Vegetable Farms in the Northeast USA which can, of course, be modified for those of us in other regions.

Nematodes

I’ve written here before about our struggles with root knot nematodes in our hoophouse, and you can read everything I know about nematodes in my book The Year-Round Hoophouse. Nematodes are only active in warm weather, and we have not had problems with them outdoors yet, but of course, it’s warmer in the hoophouse!

Cucumber roots with nematodes (see circles).
Photo Pam Dawling

My article on nematodes in Growing for Market  in November 2014 describes our discovery of the beasties and our first attempts to deal with them. My most thorough blogpost about nematodes was for Mother Earth News  Managing Nematodes in the Hoophouse.

Good news – great hoeing weather! Bad news – more nematodes in the hoophouse August 2014 includes a photo of our first attempt at solarizing – a  bit of a How Not To! There is info on dealing with nematodes from Garry Ross in Hawaii, where nematodes are a fact of daily life, in my post Cold weather, snow, thinking about nematodes from February 2015.

Warm-weather cover crops that resistant or deter nematodes include sesame, Iron and Clay cowpeas, some OP French marigold varieties (but avoid Tangerine Gem or hybrid marigolds); chrysanthemum; black-eyed Susan; gaillardia (blanket flower, Indian blanket); a sesame/millet mix, sunnhemp, partridge pea, California poppy. Some of these require a long growing season to achieve much. See Solarization and crop choices to fight nematodes.

 Cover Crop Planning

My book Sustainable Market Farming has a chapter on cover crops and 9 pages of charts about particular options.

Cover of managing Cover Crops Profitably book from SARE

The book Managing Cover Crops Profitably (third edition) from the Sustainable Agriculture Research & Education Program (SARE), is the best book I know on the subject. You buy the book for $19 or download it as a free PDF from SARE.

See Harvey Ussery in  Four Outstanding Cover Crops for Summer.

“Too often, gardeners practice cover cropping only in the off-season — for instance, to protect soil in winter — and assume it’s not a summer option. But it is, and planting summer cover crops provides big payoffs.

We too often think gardening reduces soil fertility, but in fact, the more you keep live plants growing, the richer your soil will become. Roots exude substances that feed beneficial soil organisms, including the amazing mycorrhizae (see Mycorrhizal Fungi: The Amazing Underground Secret to a Better Garden). Deep-rooted plants draw minerals from subsoil, which makes the minerals available to shallow-rooted crops. Dead plants, including invisible roots, decompose and release nutrients for use by subsequent crops. Plants also prevent soil erosion, and decomposing roots open channels for oxygen and rain, and provide pathways through which earthworms and other important organisms can migrate. Repeated seasons of organic matter deposition will increase soil carbon, or “humus,” which is crucial to soil fertility, friable texture and water retention.”

 

Cover Crops for June – Sunn hemp

 

Sunn hemp flowering in November at Nourishing Acres Farm, NC. Photo Pam Dawling

Focus Cover Crop for June: Sunn hemp

Last month I wrote about buckwheat. For small areas that will be needed back in production soon, buckwheat continues to be a good choice, unless irrigation is in short supply. You don’t get much biomass from buckwheat in a drought!

In June we are mostly looking for cover crops that will grow in hot weather. One we have recently started to use in our hoophouse is Sunn hemp (Crotalaria juncea). It looks promising as an outdoor cover crop here too. Sunn hemp is not at all related to cannabis – don’t smoke it.

Sunn hemp, a tropical legume, can grow as tall as 9’ (2.7 m) in as many weeks.  It needs 8-12 weeks frost-free to grow to full productivity. In the US it is grown as a summer annual, except in Hawaii, where it can be grown to seed at lower elevations. With adequate moisture, temperature and fertility, researchers have recorded a growth rate of 1 foot per week. It comes from India, where it is grown for fiber production and as a forage, as well as a cover crop. It is recommended for warm season use in US hardiness zones 8-13, but has been successfully cultivated as far north as Washington State.

Sunnhemp cover crop at Nourishing Acres Farm, NC.
Photo Pam Dawling

Benefits of growing sunn hemp

If you sow sunn hemp in a summer gap between spring and fall vegetable crops, it will provide a nitrogen boost for the fall crop, because it is a legume. Also, as a branching vertical plant, it avoids the problems of sprawling legumes. In dense plantings, it can fix more than 120 lbs (54 kg) of nitrogen and 12 pounds of biomass per 100 sq ft (0.56 kg/sq m). It can fix over 100 lbs of nitrogen and produce over 5000 lbs of biomass per acre (112 kg/ha and 5604 kg/ha respectively).

Most studies of vegetables grown following sunn hemp have found higher vegetable crop yields, because of the nitrogen boost, and the large amount of biomass increasing the soil organic matter. The large production of biomass means it is useful as a way to sequester carbon. The well-developed root system with a strong tap root also provides erosion control.

Sunn hemp suppresses weeds and also conserves soil water, storing summer rainfall for fall crops, and reducing runoff. Sunn hemp may enhance soil microbiota. Sunn hemp residue contains allelochemicals, that inhibit or delay germination of weed seeds and small crop seeds. Because of this, do not sow small-seeded crops or cover crops for several weeks after incorporation.

Sunn hemp suppresses plant-parasitic nematodes such as root-knot (Meloidogyne incognita) and reniform (Rotylenchulus reniformis) nematodes by producing allelochemicals that disrupt nematode life cycles. It promotes the growth of both antagonistic microorganisms and beneficial nematodes. Pest nematode numbers can be reduced for several weeks after incorporating sunn hemp into the soil. (I was disappointed to read “weeks” rather than “months” as I was hoping, although the EDIS ENY-717(see resources section) offers “a few months”)

Variation in spring field corn root development at harvest following various summer cover crops. Preceding cover crop from left to right: sunn hemp (residues mulched in), pearl millet without fertilizer, sorghum-sudangrass, corn, pearl millet with fertilizer, and sunn hemp (residues harvested).
Credit: Z. J. Grabau, UF/IFAS

Sunn hemp can be grown as a wind break to protect sensitive vegetable or flower crops, or young trees. Mow or cut the sunn hemp at 60 days, or lop the tops, to prevent too much shading.

Sunn hemp seeds at the start of a seed germination test. Photo Pam Dawling

Sowing sunn hemp

Sow sunn hemp starting a week after your sweet corn sowing date, up to 9 weeks before your first fall frost, when it will die. A soil temperature of 68°F (20°C) or more is good. It tolerates a wide range of soils (but not if waterlogged), doing better in poor sandy soils than most crops. Water for the first two weeks of growth, but do not overwater.

Plant inoculated seed (use the same inoculant as for southern peas) up to 1” (2.5 cm) deep, with seeds 1.5” (4 cm) apart in the row, and with rows 6” (15 cm) apart. Sowing densely (as with all cover crops) will work better to smother the weeds. On a field scale, drill at 25-50 lbs/ac (28-56 kg/hectare), or broadcast at 40-60 lbs/ac (45-68 kg/ha).

Another opportunity is to sow sunn hemp in the late summer or fall, 7-9 weeks before a frost. The frost-killed mulch covers the surface for an early spring food crop planting.

Sunn hemp seeds germination test. Photo Pam Dawling

Sowing sunn hemp in mixes

Sunn hemp and sorghum-sudangrass grow well mixed together. Try a 50:50 mix to start with.

This mixture can increase overall biomass and the diversity benefits soil microorganisms and therefore nutrient cycling. Only grow this very tall cover crop mix if you have tractor-based equipment. It is too massive to tackle with small mowers or weed whips.

Sunn hemp can also be mixed with other legumes, such as American joint vetch (Aeschynomene americana), southern peas (Vigna unguiculata), hairy indigo (Indigofera hirsuta), and slender leaf rattlebox (Crotalaria ochroleuca). This list comes from Florida and may not apply where you live. The shorter height of northern sunn hemp varieties, such as day-neutral ‘AU Golden’ and ‘Ubon’, may work better for cover crop mixtures. ‘Crescent Sunn’ is a short-day variety which will carry on growing if sown out of season.

Growing sunn hemp

Sunn hemp is fairly drought-tolerant from two weeks after germination, and requires little care. For maximum growth, irrigate until 75% of the plants are flowering (perhaps at the end of the third month), then you can stop irrigating.

Cutting the crop back at less than 60 days after sowing stimulates branching (more biomass) and more root penetration (better drainage). In our hoophouse, we have used hedge shears to do this at a nice ergonomic elbow height. Cutting at around 60 days produces long-lasting mulches that increase soil carbon. After 60 days, the stems thicken and become fibrous and high in cellulose. It is best to mow Sunn hemp before 90 days, due to the toughness of the fiber, making it hard to incorporate.

On a field scale, a roller-crimper can be used to break the plant stems, leaving a layer of mulch suitable for no-till transplanting of fairly large transplants. The sunn hemp is killed by crimping, and does not regrow.

A long bed of sunn hemp in November at Nourishing Acres Farm, NC. Photo Pam Dawling

Challenges with sunn hemp

Sunn hemp is notorious for seeds that are high in toxic pyrrolizidine alkaloids. Ingesting lots of seeds can cause damage to the liver, lungs, heart and nervous system. Susceptibility depends partly on the animal species: pigs are most vulnerable, followed by chickens, horses, cattle and sheep. Goats have the lowest risk.

Tropic Sun has reduced levels of these alkaloids, and is non-toxic to poultry and livestock. This and other southern varieties may be less tolerant to cold climates than northern varieties such as AU Golden and Ubon. AU Golden may flower 5-6 weeks after sowing

In some states (in 2005, Arkansas for example), Sunn hemp is regarded as a noxious weed, so do check the rules where you are, at your local NRCS office, Extension Service or state agricultural service. Some Crotolaria are noxious weeds, but as sunn hemp will not set seed consistently north of 28° N latitude (slightly north of Corpus Christi, TX), it has little potential for becoming a weed.

Deer and rabbits may browse on sum hemp, and some moths and pod boring insects may attack the stems, leaves or seedpods.

Sunn hemp growing in southern Florida.
Credit: Qingren Wang, UF/IFAS

More resources on sunn hemp

USDA Sunn hemp Plant Guide, 2005:

Ask Ifas: Questions and Answers for Using Sunn Hemp as a Green Manure Crop

EDIS SL 306 Sunn Hemp – A Promising Cover Crop in Florida

EDIS ENY-717 Management of Nematodes and Soil Fertility with Sunn Hemp Cover Crop.

NRCS USDA 1999 Sunn Hemp: A Cover Crop for Southern and Tropical Farming Systems

USDA Plant Materials Program

——————————————-

Secondary Cover Crops in June

In my May post I mentioned secondary cover crops such as soy, mustard, sunn hemp, and southern peas. I explained why we don’t grow mustards as cover crops (too many brassica food crops, too many harlequin bugs).

If you have only 28 days until the patch is needed for a food crop, you can grow mustards or buckwheat. Or weeds, if you’re careful not to let them seed!  If you have at least 45 days, you can grow soy or Japanese millet.

In June, legumes such as soybeans, southern peas, and Partridge pea are other good legumes to consider.

Soybeans as a cover crop
Photo agcrops.osu.edu

Soybeans are a great summer cover crop and they are also a legume, so they add nitrogen to the soil. They have good shade tolerance and tolerance to foot traffic (that is, people harvesting crops on either side). Because of this, we like using soy to undersow in sweet corn.

Iron and Clay southern peas as cover crop in the hoophouse, smothering weeds.
Photo Pam Dawling

Southern peas are another warm weather cover crop option. They are also a legume, and so will add nitrogen to the soil. Iron and Clay is the sprawly variety best known for cover crop use, but other varieties also work.

Senna Ligustrina, a native perennial legume, is another warm season cover crop possibility. I was given this suggestion last September by a reader in Florida. She suggested I look for a senna native to my region. Ernst Conservation Seeds sells Maryland Senna, which tolerates wetlands and dry roadsides. The idea here is to find a plant adapted to your region, meaning it will grow well. The other side of the coin is that if you are growing annual crops, you will need to pay attention and prevent self-seeding, unless you are able to cope with the chaos.

At Ernst Conservation Seeds, they “grow, process, and sell hundreds of species of native and naturalized seeds and live plant materials for ecological restoration, sustainable landscaping, reclamation, wetlands, and natural resources conservation.” If you are looking for some less usual cover crops seeds, this is the place to turn to.

Next month I will write about sorghum-sudangrass and the millets. If you are in a warmer climate than I am (central Virginia) or you want to consider more options, those are good hot weather grasses. Also see my post Cover Crops in Summer for much more information, including  making space, sowing small spaces and finding time for the work.

If you have only 28 days until the patch is needed for a food crop, you can grow mustards or buckwheat. Or weeds, if you’re careful not to let them seed!  If you have at least 45 days, you can grow soy or Japanese millet.

Cover Crop Planning

My book Sustainable Market Farming has a chapter on cover crops and 9 pages of charts about particular options.

The book Managing Cover Crops Profitably (third edition) from the Sustainable Agriculture Research & Education Program (SARE), is the best book I know on the subject. You buy the book for $19 or download it as a free PDF from SARE.

Harvey Ussery  Four Outstanding Cover Crops for Summer.

ATTRA Cover Crop Options for Hot and Humid Areas

Cover Crops for May: Buckwheat

Buckwheat in flower in September.
Photo Pam Dawling

This is the first of a monthly series on cover crops, which will take us through a whole year, to April 2024.

Why Grow Cover Crops?

<a title=”USDA, Public domain, via Wikimedia Commons” href=”https://commons.wikimedia.org/wiki/File:Soil_food_webUSDA.jpg”><img width=”512″ alt=”Soil food webUSDA” src=”https://upload.wikimedia.org/wikipedia/commons/thumb/8/89/Soil_food_webUSDA.jpg/512px-Soil_food_webUSDA.jpg”></a>

See my post Cover Crops in Summer.

  • Cover crops suppress weeds and provide a boost to soil organic matter.
  • Keep live roots in the ground as much of the time as possible, to feed the microorganisms in the Soil Food Web.
  • Here is a diagram of the Soil Food Web: https://upload.wikimedia.org/wikipedia/commons/8/89/Soil_food_webUSDA.jpg
  • Roots anchor the soil, preventing erosion in heavy rains.
  • Dead roots also have a role, providing drainage channels in the soil and letting air in deeper.
  • Adding organic matter to the soil is a way of sequestering carbon, as well as providing nutrients for your crops.
  • Deep-rooted cover crops draw up nutrients, bringing them up where crop plants can access them.
  • Leguminous cover crops provide nitrogen, saving imports of organic fertilizers or a big compost-making operation.
  • Too often, gardeners grow cover crop only in the off-season, to protect the soil in winter, and assume it’s not a summer option. But it is, and planting summer cover crops provides many benefits.

Focus Cover Crop for May: Buckwheat

A bed of young buckwheat with a cosmos plant to attract beneficial insects. Photo Pam Dawling

I have a blog post Buckwheat, a wonderful summer cover crop, introducing an article I wrote for Growing for Market magazine. See that post for basic details I mostly won’t repeat here.

Buckwheat (Fagopyron esculentum) is a fast-growing warm-season broadleaf annual that is a very useful cover crop. Its special strengths are in weed-suppression, attracting beneficial insects, improving the soil tilth (aggregate structure) with its fibrous roots, and extracting potassium, calcium and phosphorus from the soil to the benefit of following crops. Buckwheat is almost three times as good as barley in scavenging phosphorus, and more than ten times better than rye (a poor phosphorus scavenger). Because buckwheat is not related to any of the common food crops, it is simple to include in rotations.

Buckwheat can be sown up from your last frost up to 35 days before first fall frost. Buckwheat can close its canopy in just two weeks, preventing the soil baking in summer conditions. Because it matures quickly, and self-sows, it can be used in several successions with tilling between, to suppress some perennial weeds.

Flowering buckwheat in September.
Photo Pam Dawling

Buckwheat can do fairly well on poor soils, is tolerant of a range of soil pH and is an easy crop to deal with manually or with small-scale equipment. Even mature buckwheat plants are easy to deal with using manual or small-scale equipment. You can just pull up the plants by hand, or use a hoe or scythe to slice them off at the soil line. You can chop them into the soil, or gather them up and compost them. Or you can use a no-till method, let the dead plants die into a surface mulch and plant through them.

Buckwheat yields only a couple of tons per acre, but does it in only six to eight weeks. If you want to increase the (admittedly sparse) biomass, cut down buckwheat just before it reaches 25% bloom, to a height above the lowest leaf node. Buckwheat will regrow rapidly and you may even be able to make a second cutting.

Buckwheat also makes good food for poultry or rabbits, and chickens love the seeds. It does not provide good forage for larger livestock.

Beds of young buckwheat.
Photo Bridget Aleshire

Barbara Pleasant, in her 2009 article Cover Crops, described Rhizodeposition as a special advantage of using cover crops. Many plants release sugars and other substances through their root hairs into the soil. They are solar-powered pumps, sending energy down into the soil, causing the root tips to host colonies of useful microorganisms. As the roots move deeper, the microbes follow. With vigorous winter cover crop plants, like oats or rye, this process goes on down to 6 feet (much more deeply than you should dig). Buckwheat doesn’t go very deeply at all, but it can be working for you, which is much better than leaving the soil empty and drying out.

Buckwheat in flower in June. Photo Pam Dawling

Buckwheat Resources

Secondary Cover Crops for May

Soy, mustard, sunn hemp, southern peas are all also good summer cover crops, and I will say more about them in the next few months. See Cover Crops in Summer.

Sunnhemp cover crop at Nourishing Acres Farm, NC.
Photo Pam Dawling

Sunn hemp, a nitrogen-fixing legume from the tropics, can grow as tall as 9’ (2.7 m) in a few months. Sow sunn hemp from a week after your sweet corn sowing date, up to 9 weeks before your first fall frost, which will kill it. It tolerates a wide range of soils (but not if waterlogged). Plant inoculated seed (use the same inoculant as for southern peas) 1” (2.5 cm) deep, with seeds 1.5” (4 cm) apart in the row, and with rows 6” (15 cm) apart. Sowing densely (as with all cover crops) will work better to smother the weeds.

If you sow sunn hemp in a summer gap between spring and fall vegetable crops, it will provide a nitrogen boost for the fall crop, because it is a legume. In dense plantings, it can fix more than 120 lbs (54 kg) of nitrogen and 12 pounds of biomass per 100 sq ft (0.56 kg/sq m). 60 days after sowing, the stems thicken and become fibrous and high in cellulose; cutting at this stage produces long-lasting mulches that increase soil carbon. If you cut the crop back at a younger stage, this will stimulate branching (more biomass) and more root penetration (better drainage).

Sunn hemp cover crop at Nourishing Acres Farm, NC
Photo Pam Dawling

We have taken to sowing sunn hemp as a summer cover crop in our hoophouse, and lopping it periodically with hedge shears to an ergonomic elbow height. This is because we don’t want it to shade crop plants further back (north). The fallen tops make a nice “forest floor” carbonaceous mulch.

Mustard we don’t grow as cover crops, although I do have experience of growing it in England, where it is one of the favorite cover crops for short crop gaps, or in preparing areas reclaimed from pasture or lawn. We have too many harlequin bugs, and we hope to break their lifecycle by having a summer month without any visible brassicas. (We do often have fall brassica seedlings growing under insect netting.) Also, our “crop portfolio” has plenty of brassicas already, and we’d rather have a better rotation, with brassicas less often.

Mustards can decrease weeds, or certain pest nematodes, if you grow the right kind.

Soybeans as a cover crop
Photo agcrops.osu.edu

Soybeans are a great summer cover crop and they are also a legume, so they add nitrogen to the soil. They have good shade tolerance and tolerance to foot traffic (that is, people harvesting crops on either side. Because of this, we like using soy to undersow in sweet corn.

Southern peas are another warm weather cover crop option. They are also a legume, and so will add nitrogen to the soil. Iron and Clay is the sprawl variety best known for cover crop use, but other varieties also work.

Iron and Clay southern peas flowering in September. Photo Pam Dawling

Cover Crop Planning

My book Sustainable Market Farming has a chapter on cover crops and 9 pages of charts about particular options.

The book Managing Cover Crops Profitably (third edition) from the Sustainable Agriculture Research & Education Program (SARE), is the best book I know on the subject. You buy the book for $19 or download it as a free PDF from SARE.

See Harvey Ussery  Four Outstanding Cover Crops for Summer.

Nematode-resistant food crops and cover crops

Golden Frills and Scarlet Frills, two Juncea mustards that resist nematodes. Photo Pam Dawling

A few weeks ago I wrote about clearing tomato plants, and mentioned our hoophouse troubles with nematodes. Nematodes are tiny soil-dwelling worms that have a wide host range and are hard to control. They move only 3’–4′ (1–1.2 m) per year on their own, but people move them on shoes, tools, etc. We have had peanut root-knot nematodes (Meloidogyne arenaria) since 2011 when we found them in spinach transplants we were growing for outdoors in early spring.

My article on nematodes in Growing for Market  in November 2014 describes our discovery of the beasties and our first attempts to deal with them.

White Russian kale in our hoophouse.
Photo Pam Dawling

In my August 2014 post Good news – great hoeing weather! Bad news – more nematodes in the hoophouse I wrote about solarization to fight nematodes in our hoophouse (scroll down to the end of the post). The post includes a photo of our first attempt at solarizing – a  bit of a How Not To! Be sure to use UV-inhibited polyethylene. This year we somehow got some construction plastic mixed in. It doesn’t work! It goes cloudy (thus not heating up the soil) and it shatters into little pieces.

There is info on dealing with nematodes from Garry Ross in Hawaii, where nematodes are a fact of daily life, in my post Cold weather, snow, thinking about nematodes from February 2015.

My most thorough blogpost about nematodes was in 2018 for Mother Earth News:  Managing Nematodes in the Hoophouse.

Solarizing with clear plastic. Photo Pam Dawling

My post Solarization and crop choices to fight nematodes in August 2019 includes a photo of a much better way to solarize an individual bed. In that post I gave a list of nematode-resistant food crops, and also talked about cover crops. There is a photo of nematodes on cucumber roots there too).

Food crop choices to fight nematodes

Most resistant and most helpful are the Juncea group of mustards. I did some research into more Juncea options in Solarization and crop choices to fight nematodes. We don’t like very pungent greens, so we have not yet taken the route of planting a whole bed of Juncea types. Instead we have mapped and flagged the nematode-infested areas of our beds, and try to be mindful of what we plant in those spots. Three of our seven beds have no nematodes so far.

Open-pollinated Yukina Savoy.
Photo Ethan Hirsh

This year we looked at the nematode map we had made and decided to focus our attention on the bed with the highest number of nematode patches, and grow the most resistant winter crops (of the ones we like to grow) there. That’s the frilly mustards (Ruby Streaks, Scarlet Frills, Golden Frills, all Juncea mustards, and Mizuna, a Japonica mustard), Yukina Savoy (variously reported to be Brassica juncea,  Brassica rapa pekinensis, and Brassica rapa), and Russian kales (Brassica rapa).

Mapping nematode areas

See the post with info from Gerry Ross I mentioned above. We have previously tried for a “Two years good, One year bad” strategy. This was to grow nematode-resistant crops in the infected areas for two years, then try risking one year of susceptible crops. That was a bit demanding on careful management, and we haven’t kept that up.

Nematode map 2022

Cover crop choices to fight nematodes

French marigolds and sesame to deter Root Knot nematodes in our hoophouse. Photo Pam Dawling

A reader asked about cover crop choices to fight nematodes. In June 2019 I wrote about using marigolds, sesame, Iron and Clay cowpeas as warm-weather nematode resistant cover crops. We’ve also used winter wheat (in winter!), and white lupins (not worthwhile, in my experience). See that post for a few other ideas on nematode-fighting cover crops, and why we decided against some options. At that time, we decided not to grow sunnhemp (Crotolaria) because it is poisonous, although newer varieties of Crotolaria have lower toxin levels. More recently we have been growing sunnhemp, after I saw it growing so well in North Carolina. It is a warm-weather legume, so it is feeding the soil while tackling the nematodes. It does grow tall in the hoophouse, and we have taken to chopping it down with hedge shears to an ergonomic elbow-height every few weeks whenever it gets too tall. The cut tops create a nice “forest-floor” mulch effect. You can almost feel the extra organic matter nurturing the soil! (High OM levels deter nematodes.) 60-90 days to maturity.

Sunnhemp cover crop at Nourishing Acres Farm, NC.
Photo Pam Dawling

We previously used soybeans as a short-term leguminous summer cover crop, but they do not offer the nematode resistance. Iron and Clay, Mississippi Silver and Carolina Crowder cowpeas are all nematode-resistant and can be grown in summer instead of soybeans. Sesame is a legume that is particularly good against peanut root-knot nematodes.

Iron and Clay southern peas flowering in September. Photo Pam Dawling

See Our Organic Integrated Pest Management post for an organized approach to pest management, including nematodes.

A Florida reader gave me information about partridge peas, which I have not yet tried: After terminating cool-season brassicas and celery between April and June, their late spring sowing of partridge peas were too late this year to be productive, because the hard seed was very slow to germinate. Partridge pea could be a good cover crop for mid- to late-summer, if you scarify those hard seeds to speed germination.

Some cover crops can be alternate hosts for pathogens like cercospora, rust, or bacterial leaf spot, so be on the lookout for new problems while solving old problems. In the deep south, beans, yard-long (asparagus) beans, and cowpeas can succumb to heat, nematodes, rust, bacterial spots, and other pathogens and pests. Senna (tall) and Partridge pea can provide “chop-and-drop” organic matter as sunnhemp does. Sunn Hemp can host foliar pathogens (some possibly seed-borne), in Florida, and does not reliably form nitrogen-fixing nodules on the roots, even when inoculated. Even so, it is useful as a fast warm season green manure cover.

The flower Gaillardia (blanket flower) is a quick-to-compost, chop and drop option for late winter to late spring, It decomposes quickly, and can provide a quick green manure. Gaillardia is nematode-resistant, great for beneficials and pollinators, but is susceptible to some foliar pathogens later in the season. You can sow Gaillardia in August, or even later in fall for early spring flowering.

Due to climate change, and the more year-round activity of nematodes, pathogens, and pests in Florida, they’ve been including more nematode-resistant grasses into their rotations. We all need to be thinking more about warmer-climate options, as climate change continues to push pathogens and pests farther north, earlier each year.

Preparing for sweet corn

Our first sweet corn of the season. Bodacious
Photo Pam Dawling

Preparing for sweet corn

It’s too early for us to be planting sweet corn, but not too soon to be planning, preparing and thinking about it!

Crop Rotations and Cover Crops

Rotation Pinwheel Sus Mark Farm

If you don’t already have a crop rotation plan, this is the time to put one into place, especially if a lot of your ground is taken up with sweet corn every year! Our sweet corn occupies a lot of our space, so we pay attention to crop rotation. Corn is the only crop in the grass family that we grow, so this is not hard. We keep two or three years without corn between the corn years. Here’s the crop and cover crop sequence for each of our six sowings:

Sowings 1 & 2: The winter before the corn, we have a winter-killed cover crop of oats, (or sometimes a clover patch which has been growing all the previous year). Half the patch of this early corn is followed by oats in August and then garlic in early November. The other half gets oats and soy in August, to be winter-killed. This area will be easy to work up in early spring for our broccoli and cabbage.

Sowings 3, 4, & 5: The previous winter cover crop is winter rye or wheat with crimson clover (if we sow before 10/14) or winter rye or wheat with Austrian winter peas if after 10/15. The corn is followed by more rye or wheat and crimson clover in October. The following year we will plant potatoes here in June. The clover will have plenty of time to reaching flowering and therefore have plenty of nitrogen nodules on the roots.

Cover crop of winter rye, hairy vetch and crimson clover.
Photo Kathryn Simmons

Sowing 6: The previous winter cover crop is winter rye and Austrian winter peas. We undersow this corn with oats and soy. We mow high after harvest, and leave the oats and soy to grow until winter-killed. This patch is easy to prepare for our potatoes in March.

Late sweet corn undersown with oats and soy beans for a winter-killed cover crop. Photo Kathryn Simmons

For the later sowings of sweet corn, a good stand of a preceding winter cover crop mix including legumes can provide all the nitrogen the corn needs (100-125 lbs/acre; 112-142 kg/ha). The nitrogen nodules on the roots contain the maximum nitrogen when the legume reaches its flowering point, so this method doesn’t work for early sowings.

 No-till planting into strips tilled in a white clover living mulch sounds good but has been found tricky. Jeanine Davis addresses this in NCSU’s Organic Sweet Corn Production. The clover can out-compete the corn, become invasive and hard to get rid of. Soil temperatures will be lower (a disadvantage in spring) and slugs and rodents may increase. Trials of sowing corn into rolled and crimped hairy vetch are underway.

Undersowing (interseeding) cover crops such as white or crimson clover into the corn at the V5 or V6 stage is more successful. Ensure good seed-to-soil contact. The clover grows after the corn dies.

Some growers undersow with forage brassicas at last cultivation. Research shows this does not reduce corn yields. The forage can be harvested after the sweet corn harvest finishes.

Caring for Sweet Corn

Young sweet corn plants after imperfect hoeing.
Photo Pam Dawling

Never allow soil in corn plantings to dry out, especially with close planting. You might need more than 1” (2.5cm) per week for maximum productivity, although corn is more drought-tolerant than some crops. The most important times for watering are silking (when the silks first become visible) and while the ears are filling out. We use overhead irrigation for corn, which works well to also water undersown cover crops.

Corn plants closer than 8” will compete with each other, so be sure to thin. People used to recommend removing the suckers that came from the base of the plant, thinking it led to higher yields. This has been tested, and in fact it can damage plants and possibly even reduce yields. (Reports from Clemson and Colorado State).

Sweet corn needs cultivating at least twice, at two weeks and four weeks after sowing. Even better are four rounds: at 7, 14, 21 days and finally one around 35 days when plants are 18-20” (45-50cm) high. Corn is shallow rooted so avoid deep cultivation. We use a walk-behind BCS tiller, followed by hoeing (and thinning at the first cultivation).

Young sweet corn plants. To the right are ropes to mark rows for the next corn sowing.
Photo Bridget Aleshire

Each time we sow sweet corn, we wheel hoe or till between the rows of the previous planting, hoe and thin the plants to 8-12” (20-30 cm). We also till between the rows of the corn planting before that, hoe, and sow soybeans. Although they don’t supply the highest amount of nitrogen compared to other legumes, they are cheap, quick, somewhat shade tolerant, hinder weeds, and withstand foot traffic during harvesting.

While harvesting the corn we pull out any pigweed that has somehow survived our earlier efforts. Pigweed puts out its seeds in one big burst, so pulling up enormous pigweed is worthwhile, if it hasn’t yet seeded. Our soil has improved over the years, so it is now possible to uproot the 5ft (1.5 m) pigweeds. Sometimes we have to hold the corn plant down with our feet, but we do almost always succeed in getting the weeds out.

Silver Queen sweet corn with wilting pulled pigweed amaranth. Photo Kathryn Simmons

Flame-weeding can be used after sowing before the corn emerges, or after the crop is 2” (5cm) tall, using a carefully directed flame. See ATTRA Flame Weeding for Vegetable Crops

Sweet Corn Growth Stages

It is helpful to understand corn growth stages so that you know when the plant is most susceptible to damage, and when to take action. Corn growth stages are divided into vegetative (V) and reproductive (R). Stages are determined when at least 50% of the plants have reached or are beyond a particular stage.

Vegetative stages begin at emergence (VE), and each leaf with a fully developed collar is a new stage. Leaves within the whorl, not fully expanded and with no visible leaf collar, are not counted. Most sweet corn hybrids produce 18-21 leaves. Vegetative growth takes about 55-60 days after emergence. V3 (three leaf collars) begins 2-4 weeks after VE, and plants switch from using kernel reserves to photosynthesis and roots for nutrients.

Around V4, broadleaf weeds will stunt yields and should be removed. By V5, the numbers of potential leaves and ears are determined. Plants are 8-12” (20-30 cm) tall and the growing point may still be underground. Tillers (suckers, branches that grow from the lower five to seven nodes) appear.

V6-V8 – Beginning 4 to 6 weeks after VE, the growing point emerges above the surface, making the crop susceptible to frost, hail and winds. Beginning at about V6, the lower leaves may fall off naturally. At V7, rapid growth begins, and the number of kernel rows is determined. The number of potential kernels per row begins is set between V7-V16. By V8, the plant reaches 24” (60 cm) tall.

V9-V11 – At V9, tassels (not yet visible) and ear shoots are developing. New leaves appear every 2-3 days

V12 – The plant is 4ft (1.2 m) tall or more. Nutrients and water are important from this stage until the start of the R stages. The leaves are full-sized and about half are exposed to sunlight. “Brace roots” develop and the number of kernels per ear and size of the ear are set. Kernels can be damaged by insects and hail.

V15 – The plant is two weeks away from silking. Tassels are almost full-sized, but still hidden. Moisture and nutrient shortages now result in shorter ears and lower yields.

VT – Beginning 9-10 weeks after emergence, good pollination is essential to develop the kernels. Tassels are fully visible and silks emerge in 2-3 more days. Pollen shed begins, continuing for 1-2 weeks. Hail can be very damaging at this stage. Vegetative stages end when the corn develops a tassel (male flower). It takes about 20 days from tasseling to ripe.

Sweet corn growth stages. University of Illinois Extension

R1 – The plant has silks outside of the husks and is at its most vulnerable. Environmental conditions can greatly affect pollination. The worst is drought, which dries the silk out, reducing its ability to collect pollen falling from the tassels.

R2 (“Blister”) stage – The kernels are filled with clear liquid. About 12 days after silking, the silks darken and dry out. Stress (especially drought) can cause kernels to abort.

R3 – Milk stage – About 20 days after silking, kernel fluid turns milky, as starch accumulates. The effects of stress are not as severe after this stage, but can still lead to shallow kernels.

R4 – Dough stage – About 26 days after silking, the kernels have a dough-like consistency. Stress can produce scrawny kernels.

The dent stage (R5) and full maturity (R6) will only happen if you leave the plant to produce seed.

Corn growth stages can be estimated using corn growing degree days (GDD), accumulated daily from the date of planting. GDD are calculated by averaging the max and min temperatures in a 24-hour period. 50°F (10°C) is subtracted from that average temperature to give the GDD for the day. A Corn GDD Tool is available at the High Plains Research Climate Center. Stress, especially drought, can affect growth and GDD alone may not provide an accurate estimate of growth stage.

Some Highlights of the PASA Conference

I enjoyed attending the in-person conference of Pasa Sustainable Agriculture. This is the first conference I’ve been to in person in two whole years. PASA did a lot to ensure the conference was as Covid-safe as possible. They limited the number of attendees (there were still plenty to ensure lots of chances to exchange information). Everyone had to test on their day of travel to the conference, and speakers had to test every day of speaking. For me that was all three days. Everyone was masked, nearly all with KN95 “real” masks. The hotel housekeeping staff only came in after we left. (We could have requested the service, but, heck, I can make my own bed!) In the workshop rooms, the chairs were spaced 6 ft apart. The trade show had wide aisles, and meals could be taken out of the dining room to a quiet spot. Just getting to be there was a big highlight for me! I left feeling energized and enthused, and very grateful to the PASA team for preparing such a successful event.

There were four sessions of workshops each day, with one-hour breaks between, allowing time to visit uncrowded trade booths, catch up with old friends, and make new ones. We were well-supplied with snacks and beverages during the breaks. There were socials with more snacks at the end of the day.

I did have trouble with the conference app, but then, my phone is limited in what it can do. Likewise I failed to upload my slideshows to the platform, so I ran them off my flashdrive. My pdf handouts did make it onto the app, so if you wanted one of my handouts, you can find it there and here:

Young Yukina Savoy plants.
Photo Ethan Hirsh
Optimize your Asian Greens Production Dawling PASA handout 2022 2.10 9am
Young spinach seedlings.
Photo Pam Dawling
Winter Vegetable Production Methods From the Field to the Hoophouse Dawling 2022 2.11 9am 6 page handout
Sweet potatoes in storage. An ideal crop for winter meals, as they store at room temperature for a long time, maybe seven or eight months.
Photo Pam Dawling
Growing Sweet Potatoes from Start to Finish Dawling 4 pg handout 2022 2.12 11am.docx

Each of the ten workshop sessions had a choice of eight or nine workshops. I had thought I might hunker down in my hotel room when I wasn’t speaking, to minimize my chance of catching Covid, but as permaculture author Darrell Frey said “This feels safer than going to the grocery store!”

I enjoyed several workshops presented by others, including:

On-Farm Experience with Organic No-Till

Sam Malriat from Rodale

No-Till sequesters carbon in the soil, but simply never tilling does not improve the soil. Chemical no-till uses lots of herbicide. Don’t be obsessive about no-till. Shallow tillage can be a responsible choice, as incorporation of organic matter is valuable. Adding cover crops, compost or manure, grazing, and a good crop rotation, can increase the OM, and thus increase the soil water capacity enormously.

Crimson clover cover crop
Photo by Bridget Aleshire

To overcome the challenges of no-till, you need a very good cover crop stand that will provide a thick mulch when terminated; a competitive cash crop; a way to plant into the residue, and a back-up plan in case one of the requirements doesn’t pan out.

Sowing corn into rolled and crimped hairy vetch does not work well, because corn is a heavy feeder and not very competitive. Better is to undersow the corn at V5 or V6 (stages of vegetative growth) with white clover or crimson clover in September. It’s important to get good seed to soil contact. The clover grows when the corn dies. This is in Rodale Country in PA. If the clover can be left growing until the second year, cabbage can be transplanted into it. His slides showed the success of this system after an unpromising start.

Pumpkins can be direct seeded in crimped and rolled (or mowed) winter rye. There is a lot of difference in thickness of the mulch between rye sown in August and October.

Organic Solutions: Pest Management

Drew Smith and Emily Gantz from Rodale

There was a big drop in pesticide use in the mid 1990’s as GMO crops came in. But then a big uptick as resistance to the GMO crops developed. Currently, almost all non-Organic seeds contain neo-nicotinoids, even though they provide no economic benefits.

Crop rotation is the single most important thing you can do to manage pests. Drew showed us the IPM triangle, and we worked our way up. To succeed in preventing pest infestations, planning of all aspects of growing the crop is vital. As is regular scouting of each crop. Cultural controls include the physical aspects of the planting. Other physical controls include mechanical aspects of growing the crop. Biological controls include encourage beneficials, releasing biological agents. Greater biodiversity provides greater stability. See Cornell Entomology https://biocontrol.entomolgy.cornell.edu/index.php

Native Pollinators: Identification, Habitat Needs and Resources

Sarah Koenig and Ryan Stauffer from the Audubon Society

A bee pollinating squash.
Photo Pam Dawling

There are 4000 species of bees in the US (20,000 globally). 70% of food crop species rely on honeybee pollination to some extent. Native bees mostly nest in the ground. Don’t kill them by compaction (or weedkillers!). Use native flowers to attract native pollinators.

Using Tarps to Reduce Tillage on Small Vegetable Farms

Ryan Maher, Cornell Small Farms & Bob Tuori, Nook and Cranny Farm

More growers are trying tarping for weed control, killing cover crops, maintaining a good soil temperature, avoiding crusting and compaction, keeping beds dry enough for planting and reducing dependence on single-use plastics. Challenges include the heavy weight, the aggravation of using sand bags, especially in windy places, ponding of rainwater runoff, and the frustration of providing perfect vole habitat.

After 28 days in summer, you gain 200 GDDs. Plant-available soil N increases by 2 or 3 times from the plant residues. How soon does it dissipate after removing the tarp? Tarping for 3 weeks after shallow tilling kills the living weeds, improves crop establishment and reduces weed emergence by up to 83%. Think of tarps as a tillage tool! Do plan for weed management after removing the tarp. Pigweed and amaranth can become worse!

We haven’t tried tarps yet. Early September photo of hay mulched June-planted potatoes.
Photo Kathryn Simmons

Bob Tuori spoke about a SARE trial of tarping in the Northeast. He compared potatoes grown with and without prior tarping, both patches with and without hay mulch after planting. The tarped area needed sandbags every 10-15 ft. The tarp was removed June 4, weeds were counted June 24, then the patches were mulched. (I hope I got that right). I did not write down all the results, but the only-mulch area grew 17.4 lbs per hour of work, and the tarp-only area grew 13 lbs per hour of work. See the SARE report for the details.

Harvesting Techniques for Small- to Mid-Scale Vegetable Farms

Julie Henninger of Good Keeper Farm and Matthew Lowe

We saw good tool and equipment storage, and learned the benefits of growing head lettuce on landscape fabric (no rotten bottom leaves, no weeds). Muir is their favorite lettuce for spring, summer and fall. At $3/head, a 95ft row planted at 9” spacing earns them $1300, if they have a 15% loss.

Beautiful baby lettuce mix in our hoophouse.
Photo Wren Vile

We learned the importance of sharp knives or scissors for cutting baby greens with minimal cell damage and browning. Theirs sells at $12/pound. They grow Salanova, which brings in $1140/bed at each cutting. If they cut whole heads, these bring in $1476 per bed.

For loose carrots, they sow rows in pairs 2” apart, with 6 rows on a 30” bed, using a stale seed bed and flaming. They sell 1000 lbs per week. Julie Henninger emphasized not wasting time by setting the carrots down in piles. Minimize the number of times each crop is touched. They have modified a cement mixer to wash 25-45 lbs at a time.

Training and communication are also very important. New workers must master the task first, before chatting. Minimize distractions. Send crews out with a strong role model each, to keep the crew working at a sustainable pace. If working with a crew with diverse abilities (eg children), provide a clear short task with a beginning and an end, to give a good sense of achievement.

I also attended the Plenary, Why Is Farming So Hard & What Can We Do About It?  on Friday with Brennan Washington, Sarah Mock and Dr Jessica Gordon Nembhard, who were livestreamed and recorded.

I participated in the book swap, setting out some spare handouts I had in exchange for a couple of magazines. I enjoyed the Farm Innovations poster display of tools and techniques to improve production or save resources (or both). I liked that previous years’ posters were available as pages in several ring binders.

In the Trade Show there were 60-odd vendors. I checked in with Nifty Hoops, a company who will deliver a hoophouse and put it up for you in one day, or help you put it up, teaching as you build. We put ours up ourselves, in 2003, and we were inexperienced and slow, and had to work on it in the (hot) afternoons, after spending the mornings farming. At events when I talk about hoophouse growing, I’ve sometimes been asked if there are companies who will erect hoophouses (high tunnels), so it’s good to be able to pass on this contact. Nifty Hoops also sell interesting components such as DC-powered inflation blowers. (734) 845-0079.  They have videos on their Facebook page

I picked up some publications from ATTRA, who have supplied me with great vegetable growing info since before the internet. (We used to call them up and ask for publications to be sent in the mail).

The Mini-Treffler manual harrow

I also was fascinated by the Mini-Treffler, from OrganicMachinery.net, a manual rolling tine harrow for crops in beds.

  • The TINY Treffler is a hand drawn harrow with the working width of 80cm (2 ft 7 in), 100 (3 ft 4 in) and 130cm (4 ft 3 in)
  • Shares the same principle with the big Treffler harrows: in the row harrowing, adjustable tension and the patented tine suspension
  • Each tine follows the contour of the field and the downward pressure remains constant
  • The TINY is effective throughout the growing season in greenhouses or for small enterprises in vegetable production or seed propagation
  • Wheels extendable from one or both sides to straddle a bed

I gathered literature for our garden crew as well as our dairy, orchard and poultry people, and an assortment of free pens, notebooks, stickers.

PASA also had a virtual conference, spread out over a couple of weeks in January. I’m sure there was great information there too, but our rural internet is not up to the task of virtual conferencing, so I’m in the dark. Pasa intends to keep a virtual conference next year as part of the mix – it works better for farmers who cannot easily leave the farm, it reduces the carbon footprint of travel, and saves on travel and hotel or BnB costs. Maybe next year I’ll have better internet. Maybe Covid will have receded. This year’s conference was great! I look forward to next year’s!