A Permaculture Guide to Choosing Cover Crops

April 22, 2016

NOTE: Images in this archived article have been removed.

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One of my constant refrains is “Permaculture is a decision making tool for arriving at regenerative solutions.” Here I’m going to show how permaculture can help create strategies for deciding what cover crops to use. In permaculture, we’re always looking for potent leverage points, and soil-building is a big one. If we create fertile, water-absorbing, biology-rich soil, a lot of higher-level problems—things like insect damage, low nutrition, poor growth, and excess water use—all go away. And cover cropping, which is the use of specific plants to add organic matter and nutrients, is a great way to build soil. I use other methods, such as composting and mulching, but there’s something about having living roots in the soil that makes cover cropping extra effective. That thick network of roots is constantly exuding sugars and other microbe food, creating a life-rich rhizosphere that pumps nutrients into plants and builds a lush habitat for mycelium and other beneficial organisms.

I’m going to use cover cropping to illustrate how permaculture decision-making works. How do we design a cover cropping program? Good design has three major components: setting a goal, developing strategies, and choosing techniques. First, we already have our goal: We want to build our soil’s fertility, organic matter, and tilth. There are many strategies for reaching this goal. (A strategy is simply a plan, or, as management consultant Henry Mintzberg puts it in my favorite definition, a strategy is a pattern in a stream of decisions) Different strategies for soil building include composting, sheet mulching, chemical fertilizers, organic fertilizers, cover cropping, and several more. It may seem like those are techniques rather than strategies, but I think of them as strategies because there are so many different ways of doing each. Do any two people build a compost pile in the same way? And we have many different kinds of cover crops, and a host of ways to use them. That’s why I think of each of those as a strategy: Just because we’ve arrived at cover cropping as a way to build soil, we’re not done with making decisions. There’s a “lower” or more fine-grained level that we need to make some choices about. We need to choose the specific variety of cover crop, how and when we will plant, and how we will get that cover crop into the soil, such as by tilling, chop-and-drop, or harvesting and composting it. So we need to have some criteria in mind to help us make those decisions. That’s one of permaculture’s strong points: It gives us tools that remove a lot of uncertainty from making decisions. That lets us rest in the near-certainty that we’ve made appropriate choices.

To start that decision-making process, we first gather up information about cover crops—we make lists. The first obvious list to make is simply a compilation of all the varieties of cover crops that can grow in our conditions. A little Googling will get us there. One of my top sources of cover crop information is Peaceful Valley Farm Supply (https://www.groworganic.com). They ‘ve got a huge assortment. But a simply list of cover crop species doesn’t get us very far. We need to break it down into some categories, because we can’t just plant any old cover crop; every soil has specific needs and conditions. Fortuitously, the drop-down menu on cover crops at the above link has already done some category-making for us. They’ve divided cover crops into fall-planted or cool-season types, warm-season types, and year-round varieties. These categories give us a handy machete to begin chopping our way through the cover-crop thicket.

What other categories will be useful in choosing cover crops? Another big dividing line is between plants that fix nitrogen and those that don’t. Nitrogen-fixing cover crops are varieties that have a symbiotic relationship with specialized bacteria that can take gaseous nitrogen from the air, which plants can’t use, and transform it into nitrate, nitrite, or ammonia, which plants can take up as fertilizer. Non-nitrogen fixing cover crops are important too. They build biomass and add carbon to the soil, which feeds beneficial soil organisms, helps retain moisture, lightens and fluffs heavy soil and—oh, right—alleviates climate change by pumping carbon dioxide out of the air and storing the carbon in the soil. Most cover crop blends contain a mix of N-fixers and non-N-fixers.

A third division, near and dear to permaculturists, is that between annual and perennial cover crops. Annuals are great if we’re going to till in the cover crop or follow the cover crop with something else. But there’s a role for perennials, too, in paths or between rows of production crops, or as a constant biomass source. In a perfect world, all gardeners and farmers would be generating their own fertility on-site, not importing it from somewhere else that might be impoverished by the constant drain of organic matter. Ecological garden guru John Jeavons says that we should be dedicating roughly four to six times the area of our food garden to fertility crops to cover what we withdraw from harvesting. Before the fossil fuel era, most farms allotted more land for fertility production in the form of pasture for generating animal manure than they did for food production.

We could come up with other categories, such as soil preference (clay, silt, sand), frost hardiness, and so forth, but the three I’ve outlined above are the ones I use most often. Those categories create a two-by-two-by-two matrix or three-dimensional chart that really helps to zero in on the right choices. Let’s build that chart.

Here’s a table of over 100 useful cover crops, edited from a USDA list at http://plants.usda.gov/java/coverCrops?sort=comname

Scientific Name Common Name Plant Family
Amaranthus caudatus foxtail amaranth Amaranthaceae – Amaranth family
Amaranthus cruentus red amaranth Amaranthaceae – Amaranth family
Amaranthus hybridus × hypochondriacus Plainsman amaranth Amaranthaceae – Amaranth family
Amaranthus hypochondriacus Prince-of-Wales feather Amaranthaceae – Amaranth family
Arachis glabrata rhizoma peanut Fabaceae – Pea family
Arachis hypogaea peanut Fabaceae – Pea family
Avena sativa common oat Poaceae – Grass family
Avena strigosa black oats Poaceae – Grass family
Beta vulgaris common beet Chenopodiaceae – Goosefoot family
Beta vulgaris ssp. cicla chard Chenopodiaceae – Goosefoot family
Brachiaria ramosa signalgrass Poaceae – Grass family
Brassica hirta white mustard Brassicaceae – Mustard family
Brassica juncea brown mustard Brassicaceae – Mustard family
Brassica napus var. napus rape Brassicaceae – Mustard family
Brassica napus var. pabularia Siberian kale Brassicaceae – Mustard family
Brassica nigra black mustard Brassicaceae – Mustard family
Brassica rapa var. rapa field mustard Brassicaceae – Mustard family
Bromus hordeaceus soft brome Poaceae – Grass family
Cajanus cajan pigeonpea Fabaceae – Pea family
Camelina sativa false flax Brassicaceae – Mustard family
Canavalia ensiformis jack bean Fabaceae – Pea family
Carthamus tinctorius safflower Asteraceae – Aster family
Chenopodium quinoa quinoa Chenopodiaceae – Goosefoot family
Cicer arietinum chick pea Fabaceae – Pea family
Cichorium intybus chicory Asteraceae – Aster family
Crotalaria juncea sunn hemp Fabaceae – Pea family
Cucurbita gourd Cucurbitaceae – Cucumber family
Cyamopsis tetragonoloba guar Fabaceae – Pea family
Daucus carota var. sativus carrot Apiaceae – Carrot family
Echinochloa crus-galli Barnyard grass Poaceae – Grass family
Elymus hoffmannii RS wheatgrass Poaceae – Grass family
Elymus trachycaulus slender wheatgrass Poaceae – Grass family
Eragrostis tef teff Poaceae – Grass family
Eruca vesicaria ssp. sativa rocketsalad Brassicaceae – Mustard family
Fagopyrum esculentum buckwheat Polygonaceae – Buckwheat family
Glycine max soybean Fabaceae – Pea family
Helianthus annuus common sunflower Asteraceae – Aster family
Hordeum barley Poaceae – Grass family
Hordeum pusillum little barley Poaceae – Grass family
Hordeum vulgare common barley Poaceae – Grass family
Indigofera hirsuta hairy indigo Fabaceae – Pea family
Lablab purpureus hyacinth bean Fabaceae – Pea family
Lathyrus sativus white pea Fabaceae – Pea family
Lathyrus sylvestris flat pea Fabaceae – Pea family
Lens culinaris lentil Fabaceae – Pea family
Lespedeza capitata roundhead lespedeza Fabaceae – Pea family
Linum usitatissimum common flax Linaceae – Flax family
Lolium perenne ssp. multiflorum Italian ryegrass Poaceae – Grass family
Lolium rigidum Wimmera ryegrass Poaceae – Grass family
Lolium temulentum Darnel ryegrass Poaceae – Grass family
Lotus corniculatus bird’s-foot trefoil Fabaceae – Pea family
Lotus tenuis narrowleaf trefoil Fabaceae – Pea family
Lupinus lupine Fabaceae – Pea family
Lupinus albus white lupine Fabaceae – Pea family
Lupinus angustifolius narrowleaf lupine Fabaceae – Pea family
Medicago littoralis water medick Fabaceae – Pea family
Medicago lupulina black medick Fabaceae – Pea family
Medicago polymorpha Bur clover Fabaceae – Pea family
Medicago rugosa gama medic Fabaceae – Pea family
Medicago sativa alfalfa Fabaceae – Pea family
Medicago scutellata snail medick Fabaceae – Pea family
Medicago truncatula Barrel clover Fabaceae – Pea family
Melilotus alba white sweet clover Fabaceae – Pea family
Melilotus officinalis sweetclover Fabaceae – Pea family
Mucuna pruriens velvet bean Fabaceae – Pea family
Onobrychis viciifolia sainfoin Fabaceae – Pea family
Panicum miliaceum proso millet Poaceae – Grass family
Pennisetum glaucum pearl millet Poaceae – Grass family
Phacelia tanacetifolia lacy phacelia Hydrophyllaceae – Waterleaf family
Pisum sativum garden pea Fabaceae – Pea family
Poa pratensis Kentucky bluegrass Poaceae – Grass family
Psathyrostachys juncea Russian wild rye Poaceae – Grass family
Puccinellia distans weeping alkaligrass Poaceae – Grass family
Puccinellia nuttalliana Nuttall’s alkaligrass Poaceae – Grass family
Raphanus sativus cultivated radish Brassicaceae – Mustard family
Secale cereale cereal rye Poaceae – Grass family
Sesbania bispinosa dunchi fiber Fabaceae – Pea family
Sesbania herbacea bigpod sesbania Fabaceae – Pea family
Sesbania sesban Egyptian river hemp Fabaceae – Pea family
Setaria italica foxtail millet Poaceae – Grass family
Sinapis alba white mustard Brassicaceae – Mustard family
Sorghum bicolor sorghum Poaceae – Grass family
Sorghum bicolor × S. bicolor var. sudanense Sudex (Sorghum-sudangrass) Poaceae – Grass family
Sorghum bicolor var. bicolor × bicolor var. sudanense Sudex Poaceae – Grass family
Spinacia oleracea spinach Chenopodiaceae – Goosefoot family
Thinopyrum intermedium intermediate wheatgrass Poaceae – Grass family
Thinopyrum ponticum tall wheatgrass Poaceae – Grass family
Trifolium alexandrinum Egyptian clover Fabaceae – Pea family
Trifolium ambiguum Kura clover Fabaceae – Pea family
Trifolium fragiferum strawberry clover Fabaceae – Pea family
Trifolium hirtum rose clover Fabaceae – Pea family
Trifolium hybridum alsike clover Fabaceae – Pea family
Trifolium incarnatum crimson clover Fabaceae – Pea family
Trifolium pratense red clover Fabaceae – Pea family
Trifolium repens white clover Fabaceae – Pea family
Trifolium subterraneum subterranean clover Fabaceae – Pea family
Trifolium vesiculosum arrowleaf clover Fabaceae – Pea family
Trigonella fenugreek Fabaceae – Pea family
Triticosecale rimpaui triticale Poaceae – Grass family
Triticum aestivum common wheat Poaceae – Grass family
Urochloa ramosa browntop millet Poaceae – Grass family
Vicia atropurpurea purple vetch Fabaceae – Pea family
Vicia benghalensis purple vetch Fabaceae – Pea family
Vicia faba fava bean Fabaceae – Pea family
Vicia grandiflora large yellow vetch Fabaceae – Pea family
Vicia sativa garden vetch Fabaceae – Pea family
Vicia villosa winter vetch Fabaceae – Pea family
Vigna radiata mung bean Fabaceae – Pea family
Vigna unguiculata cowpea Fabaceae – Pea family
Vulpia myuros annual fescue Poaceae – Grass family
Zea mays corn Poaceae – Grass family

Next we need to organize these by dividing them up into our matrix. We’ve got 3 categories and two choices in each category.

  • N or B: nitrogen-fixer or biomass accumulator;
  • W or C: warm season or cool season; and
  • A or P: annual or perennial.

Two choices in each of three categories makes eight possible combinations in our matrix, which I will label like this:

  • NCA (N-fixer, cool season, annual)
  • NCP (N-fixer, cool season, perennial)
  • NWA (N-fixer, warm season, annual)
  • NWP (N-fixer, warm season, perennial)
  • BCA (Biomass, cool season, annual)
  • BCP (Biomass, cool season, perennial)
  • BWA (Biomass, warm season, annual
  • BWP (Biomass, warm season, perennial).

We can organize those eight combinations in a matrix:


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And now we need to split our cover crop variety list into those eight categories. I’ve created a table, below, with the cover crops divided into annuals, perennials, N-fixers, and biomass plants, but having spent more time on this post than I intended to, I haven’t divided them into warm and cool weather crops. Sample cool weather cover crops are fava beans, winter wheat, and vetch. Warm weather cover crops include alfalfa, sudan grass, and buckwheat. Interested readers can use the catalog and tables from Peaceful Valley Farm Supply or other sources on the web to create the remaining categories. Or maybe I’ll get around to it someday.

N- fixer, Annual N-Fixer, perennial Biomass, annual Biomass perennial
arrowleaf clover alfalfa annual fescue browntop millet
chick pea alsike clover barley chicory
cowpea bigpod sesbania black mustard Intermediate wheatgrass
crimson clover bird’s-foot trefoil black oats Italian ryegrass
Egyptian clover black medic buckwheat Kentucky bluegrass
Egyptian river hemp bur clover carrot Nuttall’s alkaligrass
Fava bean Flat pea ceral rye  
fenugreek jackbean Chard  
gama medic Lablab bean Chickpea  
garden pea lupine common barley  
garden vetch narrowleaf lupine common beet  
guar narrowleaf trefoil common flax  
hairy indigo red clover common oat  
hyacinth bean sesbania common sunflower  
Kura clover sweetclover common wheat  
large yellow vetch white clover corn  
lentil white sweet clover cultivated radish  
mung bean   Darnel ryegrass  
peanut   False flax  
pigeon pea   Field mustard  
purple vetch   foxtail amaranth  
rhizoma peanut   foxtail millet  
rose clover   gourd  
roundhead lespedeza   lacy phacelia  
sanfoin   little barley  
snail medic   pearl millet  
strawberry clover   plainsman amaranth  
subterranean clover   Prince-of-Wales feather  
sunn hemp   proso millet  
velvet bean   quinoa  
water medic   rape  
white lupine   red amaranth  
white pea   rocketsalad  
winter vetch   RS wheatgrass  
    Russian wild rye  
    Siberian kale  
    slender wheatgrass  
    Sudex (Sorghum-sudangrass)  
    tall wheatgrass  
    weeping alkaligrass  
    white mustard  
    Wimmera ryegrass  

I hope you find this useful. Permaculture really can be a great decision-making tool.


Photo credit: By USDA NRCS South Dakota – Cover Crops in Northwestern South Dakota 2015, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=48210676

Tags: building resilient food systems, permaculture