SUMMER COVER CROPPING

Cover cropping is a site-preparation technique that consists of planting annual or perennial herbs with an aim of keeping the soil covered, suppressing the weeds and improving the soil in many different ways.

Usually, cover crops grow for a set time and then they’re tilled in as a green manure/brown manure, or mowed/rolled over to create a mulch layer. But you may also use them as a permanent or transitional ground cover in your food forest (see below).

There are many benefits to cover crops, they prevent erosion, improve soil fertility, build soil organic matter, suppress weeds, loosen compacted soils, break pest cycles, and provide pollen, nectar and wildlife habitat…The actual benefits will depend on the type of cover crop species you use and for how long they grow.

You can use cover crops in your 1. garden, 2. field crops or pastures and 3. food forest.

1. Garden – here we plant green manures, fast-growing plants sown to cover bare soil and rebuild the organic matter and fertility of the garden beds. These are usually sown in late summer or autumn after the harvest and terminated in spring prior to planting veggies.

To learn more about green manure in this context see: Sow Green Manure Crops.

2. Field Crops/Pastures – here we plant diverse cover crop mixes in order to improve soil and the yield of subsequent crops. These are sown as part of cropping systems and are terminated at different parts of the year as necessary.

3. Food Forest – here we use cover crops as green/brown manures for soil improvement prior to planting trees and shrubs, or use them as transitional or permanent ground covers around already planted food forest trees and shrubs.

How to design your cover crop mix

 

What you’ll need?

Estimated cost: $20 – $60 / Acre

STEP 1: What are your goals/resource concerns?

There are many cover crops you could use. Therefore, in order to choose the most suitable ones you’ll need to be clear on your goals and problems you’re trying to address.

Gabe Brown said, “You don’t just seed the cover crops, you design for what you don’t have.” So think about specific goals/resource concerns that your site has and the current state of the soil you’ll be improving. These can be any of the list below and others that are specific to your context.

  • Provide nitrogen
  • Provide weed control
  • Improve soil structure
  • Reduce soil erosion
  • Add organic matter
  • Integrated pest management
  • Enhance pollinators
  • Wildlife winter food and shelter
  • Livestock integration
  • Compaction breaking

In most cases, you’ll have multiple objectives; that’s okay, but narrowing your goals/resource concerns to one or two primary and perhaps a few secondary goals/resource concerns will greatly simplify your search for the best cover species.

STEP 2: Context / my environment – my plan or logistics

Before you select your seeds, buy your cover crop mixtures and sow anything think about the logistics of your project. You don’t want to throw money down the drain because of some implementation/management concern you didn’t account for.

Think about these questions:

  • What’s your climate like? When you sow your cover crops are you going to get the rainfall or will you have to irrigate? Can you irrigate if necessary?
  • What’s the ground like? Can you till or disturb the soil to sow your cover crops on bare soil or will you have to overseed them into the existing vegetation?
  • What’s your seeding method? Depending on the size of the area you’ll seed with the cover crops you might want to spread the seeds differently. Do you have the needed equipment and labor?
  • How and when will you terminate the cover crops? Some plants will be killed off by summer heat, some by the winter cold, some will persist for a while, some will become weedy if not deliberately killed off and incorporated into the soil. You need to have a plan in place for this.

STEP 3: Choose your plants and design your cover crop mix

Now you can design your cover crops to address whatever specific concerns you outlined in the Step 1.

There are many types of plant you can use and, generally, we can split them into three groups: 1legumes, 2. grasses and 3. other crops.

1. Legume cover crops such as clovers, hairy vetch, peas, beans, lupins… are primarily used for their ability to fix atmospheric nitrogen (N) with the help of bacteria and add it to the soil. They vary widely in their ability to prevent erosion, suppress weeds and add organic matter to the soil.

2. Grasses such as annual cereals (rye, wheat, barley, oats) and forage grasses (ryegrass, sorghum–Sudan grass) are primarily used for biomass production and weed or erosion control. Because of their high carbon content, they break down more slowly than legumes, resulting in longer-lasting residue (mulch).

3. Other cover crops such as brassicas, mustards, dynamic accumulators in general can fulfil other functions such as biofumigantion (rape and other brassica crops are good at suppressing soil pests), accumulating minerals from the subsoil (comfrey, chicory, plantain send deep roots down seeking nutrients…), production of root biomass…

Some of all these above will also be suitable for attracting beneficial insects.

Use this list to design your own cover crop mix.

General guideline on making the mix:

  • If you’re designing a transitional or permanent cover crop layer for your food forest use up to five perennial crops. 
  • For all other summer cover crops aim to have at least five warm season species in the mix. 
  • Balance is important. Too much N-fixing of cover crops can actually deplete more organic matter than it adds. For this reason, your mixes in addition to species that fix nitrogen should contain 10-40% grasses or other non-legumes.
  • For the best results you should make multi-species cocktails choosing species from all three groups. The more varied the mix, the more varied the soil life’s diversity is, the better the job it does of suppressing weeds, the better the drought resistance, and the better the overall soil health!
  • Don’t try to make exotic mixes that will cost you too much money, think about the cost and availability of the selected cover crops. In total you’ll need minimum of 20 pounds ~ 9 kg of seeds per acre. If you’re seeding a large area use cheap and easily available species!

STEP 4: Acquire your seeds

Now when you designed your cover crop mix you’ll need to find the seed suppliers and place your orders.

If you are not sure where to start your search, here’s a list of seed companies we can recommend. Some of them will have a dedicated cover crop section on their websites.

Note: This growing database is periodically updated, we also accept your recommendations, so if you want to add a reputable supplier click here.

How to sow cover crops on the site

 

What you’ll need?

  • Ground cleared of low vegetation
  • Seed mix
  • Sand
  • A bucket or seed broadcasting equipment

STEP 1: Site prep

In preparation for sowing your cover crops you’ll have to do some pre-work, the extent of this will depend on the size of the area and type of sowing method you’ll use.

If you’ll be overseeding/frost seeding into existing low-growing vegetation the prep work is fairly minimal and boils down to cutting, mowing, grazing the existing plants down as low as possible. This will give the cover crop seeds a fighting chance to establish and take over.

In all other scenarios you should sow your seeds on bare soil. To do this, you have several options:

  • The conventional tilling method — shallow tilling the ground or removing the sod by hand or machines. Note that tillage only needs to be as fine as the seeds to be planted.
  • Sheet mulching — a no-till method where you use a sheet of cardboard, newspaper, flax or hemp matting, or even an old carpet, to kill existing vegetation, the downside is that this usually takes a few months.
  • Sheet mulching + compost on top — add compost on top of the sheet to get a clean seedbed immediately. Works well on smaller sites.
  • Soil prep with animals — using small and large livestock to “till” the ground and remove the existing vegetation.

Ideally, I would recommend watering beforehand, so the soil is moist, or do the soil disturbance after a rain event.

STEP 2: Prepare the seeds

  • If necessary, inoculate the legume cover crop species with the proper strains of the bacteria prior to planting. Since most soils do not contain very many, if any, N-fixing bacteria, unless your seeds are insulated there will be no nitrogen fixation. Some seeds are already coated in an inoculant, but some are not, so be aware of that.
  • Grab a bucket and mix together all of your cover crop seeds and dry fine sand. The sand will help you to broadcast the seeds more easily and not to run out of seeds too soon!

STEP 3: Sow/broadcast the seeds

Now it’s time to broadcast your cover crop seeds evenly over the whole area prepared for sowing.

  • On a small scale, you can do this by hand; hold the bucket next to your body with one arm, and grab handfuls of the mixed seeds in your other arm, throwing them to the left and right of your path as you walk forward. Cover the entire area with parallel paths.
  • On a larger scale you can use a hand-cranked seed-broadcasting machine (‘seed fiddle’) or other seed-broadcasting equipment. Fill it with the seed, and the machine sits on your chest as you walk forward, turning the handle. This will allow you to control and adjust the rate at which the seeds are broadcasted.

 

STEP 4: Improve the seed germination

In most cases, especially if you’re cover cropping at a bigger scale, you can leave everything as-is, but if you want to ensure better germination, improve resistance to drought and excess rainfall, and to exclude bird predation…

  • Make sure that seeds are either incorporated into the soil to a proper depth, or at least covered with a thin layer of straw mulch (1 bale of straw per 40m2).
  • Rolling or lightly trampling the seed into the soil surface increases the germination, as well as watering regularly, which then helps the seeds stick to the ground.

Note: even without these measures, you’ll still get a good percentage of germination. 

STEP 5: Terminate the cover crops (if applicable)

Depending on the type of cover crops you’ve sown and your plans you might want to terminate your cover crops at a certain stage of their lifecycle.

Cover crops are usually killed before or during soil preparation for the next crop or next stage of the food forest evolution.

You can, however, leave cover crops growing, let them flower, attract polluters and other beneficial insects, and reseed. However, this way, some of them can become unwanted weeds (especially in the case of buckwheat, ryegrass, crown vetch, and hairy vetch). But on the other hand, natural reseeding might be beneficial in some situations.

If you decide to terminate your cover crops you can:

  1. Plow, roll and crimp them into the soil,
  2. Mow and leave as mulch,
  3. Graze with animals,
  4. Let nature do its work with winter or summer kill,
  5. Let them grow to maturity, if they are annual crops they’ll die on their own.

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