Cover cropping and green manuring are good gardening practices for a number of reasons: they improve soil structure and fertility, increase organic matter, loosen compacted soils, reduce weeds, control erosion, and attract pollinating insects. Although the two terms are often used interchangeably, generally speaking, green manures are tilled into the soil while they are still green and growing, while cover crops are planted for ground cover, erosion prevention and nutrient retention (holding nutrients in the soil that may otherwise be leached away).
While gardeners are often aware of their many benefits, we can find it difficult to integrate cover crops and green manure into our garden spaces without decreasing the food production that is the main goal! So let’s take a look at a couple of ways in which you can incorporate these practices into your garden while improving the overall quality of the soil and thereby increasing yields.
I f you have plenty of growing space, or new ground that you can break into, then you have the option of dividing your garden into two plots – ½ for your food production and ½ for a succession of green manures, alternating each year (more on this later). On the other hand, if you have no room for expansion, you can utilize the nitrogen fixing capabilities of your pea and bean crops by planting these in the same spot in your garden back to back. For example, begin in the spring by planting your peas. Once you have harvested your all your peas, pull up the plants and sow beans in the same spot. After harvesting the beans, incorporate the plants into the soil and allow them to break down. Rotate these legumes to a new location in your garden each season in order to fix nitrogen in a different place each year.
Besides figuring out which kinds of cover crops work best within your garden’s space allotment, you’ll also need to determine which cover crops fit best with your tillage system. For a home gardener using only hand tools, annual cover crops that winter-kill, such as annual ryegrass, oats and peas, are easier to work with than perennials, like winter rye and hairy vetch, which require a lot more labor to manage. The latter can easily claim territory in your garden and become a persistent perennial problem, and I only recommend them if you have access to mechanical means of tilling in your crop, such as a rototiller or garden tractor (and even then they can be difficult to manage).
If your garden or farm is non-mechanized, and you use only hand-tools:
- Prep your beds with a digging fork to prepare for seeding; try turning only the top 2-3” of soil so as not to disturb the dormant weed seedbed.
- Select your cover crop/green manure (see below)
- If you are using a legume as one of your cover crops, applying inoculant to the seed immediately before planting will aid in fixing nitrogen from the air and bringing it into your soil. Lightly moisten seed and mix with appropriate ratio of inoculant for the amount of seed (usually indicated on the package). Nitrogen is fixed via a symbiotic relationship between nodules on the roots of leguminous crops and Rhizobium bacteria present in the inoculant and is often naturally occurring in your soil.
- Toss seed over prepared ground as evenly as possible and gently rake into the soil. Follow the recommended seeding rate for the crop you are using. Be sure to get ample coverage for weed suppression since it is easy for weeds to grow and go to seed inside your cover crop stand without you knowing it. If you broadcast your cover crop heavily, it will out-compete the weeds, and deprive them of the moisture, light and nutrients that they need to complete their life cycle.
- Hopefully, after following these steps you will get a nice, lush, dense cover crop stand. See specific crops below for instructions on the final step of incorporating the cover crop into your soil.
Two cover crop options for non-mechanized gardens/farms:
- Buckwheat is a quick-growing, warm season crop well-suited to loosening clay soils and suppressing weeds. Its small white flowers are very attractive to pollinators, but be sure to kill/till before it goes to seed or it will self-sow and become a weed problem. Buckwheat is frost sensitive, so make sure you sow after your area’s frost-free date. 2 ½ to 3 months later – once it has begun to flower but before any goes to seed – you can pull it up the stalks by hand – especially if your soil is somewhat moist (after a light rain it should come out of the ground easily) – and add the buckwheat to your compost pile. Or, mow the buckwheat (to chop it up into smaller pieces, which will allow it to break down faster) and incorporate with a digging fork into your soil. In this case, you will need to allow time for it to break down into the soil before planting into that bed. If you have a desire a regrowth of buckwheat, simply mow before it flowers and you will get a second succession.
- Oats/peas If you live in an area where the temperature dips below 20◦, Oats and Peas will winter-kill, which makes for easy incorporation in the spring. If the temperatures do not get that low in the winter, then you will need to mow and incorporate the oats/peas in the spring before planting (see instructions for rye/vetch below). Simply sow the seed six to ten weeks before first frost date (you want to allow enough time to get a good stand); the peas will fix nitrogen while the oats generate organic matter. When the temperatures drop, the oats and peas will die down, falling to create a plant mat on top of your soil. This mat, and the roots below, will serve to protect your soil from erosion. They will also begin to break down. In the spring, this mat will be partially decomposed and you can use your digging fork to turn the rest back into the soil.
For a mechanized garden, with a rototiller:
- Use any of the methods above. In addition, you can make use of a mower and rototiller to more quickly incorporate the plant matter back into your soil.
- Oats/peas can be sown in the spring. Mow before the peas begin to flower and incorporate with your rototiller, or leave the plant matter on the surface of your soil as mulch and transplant directly through it (hand-tool gardeners: this method works will for you too!)
- Winter (or cereal) rye/vetch are seeded in the fall. The crop grows well in cool weather and will establish itself in the fall, lie dormant for the winter, and start to grow again in the early spring. You can mow several times throughout the season for several regrowths or just mow once in the spring (after rye has surpassed 12”) and incorporate into the soil. Allow time for the plant matter to break down before planting your food crop. Allelopathic effects and nutrient tie ups can impede growth of the crop that follows if you don’t allow time for the cover crop to break down a bit. Rye can be tenacious and really needs to be incorporated into the soil in order to die-back, so it can potentially present a challenge when incorporating it without a tractor.
- Ryegrass is a quick growing annual grass that is great for suppressing weeds, controlling erosion, and adding organic matter. It can also be sown in your walk rows and mowed with a lawn mower.
With a little extra effort and physical labor, you can largely reduce the costs associated with importing expensive fertilizers by growing your own organic matter. And any way in which you incorporate these beneficial practices, however great or small, will improve the overall health and vigor of your garden.
For more information about all of the cover crops mentioned above, including seeding rates, quantities of dry matter produced, recommended zones and more, check out the book “Managing Cover Crops Profitably”.
Also, to order organic cover crop seeds, please visit our Organic Cover Crops section of our website.
(this post was originally posted in our on-line e-newsletter The Seed Bin – March 2011)