Sow green manure crops

Green manures, also known as cover crops, refer to fast-growing plants, mainly grasses and legumes, sown to cover bare soil and rebuild the organic matter and fertility of the garden beds.

These are sown immediately after the harvest, usually in late summer or autumn, and then terminated in late winter or early spring prior to planting veggies. However, you could use cover crops at any time of the growing season when you want to give your garden beds a break, while improving the soil in various respects.

Because growing vegetables is very demanding on the soil it depletes it of organic matter and nutrients. To keep the productivity high you need to revitalize the soil after each harvest. Adding compost, animal manure and other amendments as part of your spring and fall garden prep is a quick and easy way of doing this, but you could also sow green manure crops as a part of this soil revitalization process.

They will add organic matter and nutrients to the soil, and, in addition to that, they can fulfil other useful and beneficial functions. They can suppress weeds and stop soil erosion, break up hard, compacted soils, protect the soil from the baking rays of the sun or winter cold, and provide a habitat for beneficial insects above- and underground.

The main disadvantage of using green manures is that they take up growing space that you would otherwise use for growing vegetable crops. And they take time to grow, from six weeks to a whole season, depending on the plant.

But considering the benefits and the fact that they are produced onsite and require no work other than seeding the crop, shredding it and mixing it into the ground, they are a great addition to our permaculture gardening toolbox.

Note that, in order for green manures to become well established, you’ll need to sow them at least six to four weeks before the first fall frost. If you are late on this deadline you can opt for a very early spring cover crop, seeded as early as the winter weather allows and incorporated into the soil before the first direct-seeded crops are started.

What you’ll need?

Equipment/Tools:

  • Sharp hoe or spade.
  • Landscaping rake (optional).
  • Garden shears.

Materials:

  • Seed (or seed mix).
  • Sand (optional).
  • Bucket for seed broadcasting (optional).

 

RECOMMENDED COVER CROPS:

What type of cover crops or green manure crops you’ll use in your garden depends on your goals and the problems you’re trying to address.

Here are some of the most common ones used by gardeners alongside the types of issues they’ll help you deal with. For a more detailed overview of all the cover crops available check out this list.

Buckwheat

Warm season cover crop, highly sensitive to frost. Useful for rapidly covering the soil and crowding out weeds. Goes to seed eight to ten weeks after being seeded, so you’ll need to dig it under before then.

Field Peas

Hardy nitrogen-fixing green manure crop. You can use it to bulk up your soil in spring, summer, or fall. Produces a good supply of organic matter. Dig them under before they go to flower in spring, or after the pea harvest. Needs a companion crop to climb on (see oats).

Hairy Vetch

Hardiest nitrogen-fixing green manure crop. Useful for winter cover cropping. Requires eight weeks to grow before being turned under. Dig in spring before it goes to flower. Needs a companion crop to climb upon (see oats).

White Clover

Hardy nitrogen-fixing green manure crop. Slow to establish and difficult to get rid of. Useful in situations when you want to let a garden bed rest for a full year and perform minimum maintenance (little mowing per year). Since the seeds are so fine, mix it 50/50 with sand before broadcasting it.

Winter Rye

Hardy grass that produces a lot of biomass, smothers weeds and improves the soil structure. Useful for winter protection of the empty garden bed. Requires four to six weeks to develop, and grows even in cold conditions. Cut down or mow in spring before seeds set, and then till under.

Oats

Hardy grass that adds biomass to the soil, smothers weeds and improves its structure. Particularly useful as a legume companion/nurse crop, either with field peas when it’s seeded in early spring or with hardy vetch when it’s seeded in the fall. Both mixes require eight weeks to grow before being turned under.

STEP 1: Prep the garden beds

Remove all weeds and plant debris from the garden bed.

  • Start by pulling out and clearing all the previous crop from the bed. Pull from the base of the plant and shake off the soil so that you’re not moving soil around.
  • Then pull all weeds from the bed, and make an effort to dig their roots out. This will provide a head start to your cover crops that will then outcompete and overcrowd any possibly remaining quick-sprouting weeds.

 

STEP 2: Prepare for broadcasting seeds

  • If necessary, inoculate the legume cover crop species with the appropriate 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 this.
  • Check the recommended seeding rates for broadcasting the cover crop in question.
  • If you are mixing cover crops together or with sand, grab a bucket and mix them together according to the recommended seeding rates.

STEP 3: Sow/broadcast the seeds

Now it’s time to broadcast your cover crop seeds over the whole garden bed area.

  • Grab a handful of seeds and throw them onto the ground, make sure to cover the whole bed evenly.

 

STEP 4: Improve the seed germination

  • To help ensure good germination, mix the seed into the soil. You can do this by hand, landscape rake or a wheel hoe.

Make sure that seeds are incorporated into the soil to a proper depth.

STEP 5: Water the beds

In the case of extended periods of hot or dry weather you’ll need to provide water for seeds to germinate. This is most likely to happen during the summer cover cropping period, as in the fall the moisture in the soil is usually good enough for proper seed germination.

STEP 6: Mow the cover crops

After a period of growth, and before the plants go to seed, it’s time to mow the cover crop. Ideally do this 2-3 weeks prior to planting the bed.

  • For this you can use a garden shears and chop it a couple of inches/5-10 centimeters above the soil. Once the cover crop is bunched on the ground, chop it once more.

Note: To release the maximum amount of nitrogen from leguminous cover crops the best time to mow them is just before they flower. At that stage the plant has stored its maximum nitrogen and will make the greatest contribution to soil fertility.

STEP 7A: Cover the bed with a tarp (optional)

You now have two choices; you can either till it into the ground or leave it on the surface and cover it with a black tarp.

By covering it with a tarp you let it decompose with the help of microbes and soil organisms over a period of time.

  • If you go down this route, put the tarp over the garden bed and make sure it won’t move. Weigh it down with stones, branches or pin it down with ground-cover pegs, ‘staples’ made of wire.

 

STEP 7B: Turn under the cut cover crop

Now shallowly mix the cover crops into the soil.

  • Use a sharp hoe or spade to chop into the stubble and to cut the root mass which surfaces during the hoeing.

Any plan residue still visible after the chopping will break down quickly, so don’t worry about fine chopping everything.

STEP 8: Allow some time before replanting the bed

Now that you have provided soil organisms with some fresh organic matter, you’ll need to give them time to decompose it.

To completely break down the green manure and make nutrients available to the plants give them 2-3 weeks before planting your bed with vegetables.

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