Don’t Garden Naked: Cover Crop!

Posted: February 19, 2013

Don’t garden naked.

This is the (slightly modified) motto of cover crop advocates, particularly the Practical Farmers of Iowa who actually sell T-shirts (organic, of course) that say “Don’t Farm Naked: Plant Cover Crops.” But cover crops aren’t just for large-scale farmers! Home gardeners everywhere should know: cover crops are the best way to dress up your soil for winter or for many occasions in between.

Cover crops are an economically and environmentally sound way of improving your soil fertility, even on a small scale. No shoveling horse manure or applying petroleum-derived amendments necessary. Cover crops offer an easy way to improve your soil, reduce weeds and manage nutrients.

Some easy principles to remember when using cover crops in the home garden (Sarrantonio, 1994):

Timing – Choose your niche and plant the cover appropriately so that it will grow rapidly, covering the ground and suppressing potential weeds.

Selection- Choose a species that will thrive in your timing niche. For example, cool season cover crops should not be planted as a summer cover crop.

Don’t scrimp on seed- Read the directions and follow the seeding guidelines, planting too little seed will create gaps where weeds can thrive. Also, inoculate legumes with their appropriate bacteria to get optimal nitrogen fixation. If you get poor seed germination the first time, plant again two weeks later.

Don’t let the cover become a weed- The time to kill a cover crop is when it is blooming and before it sets seed. Be careful! Cover crops like buckwheat can have flowers and seeds on it at the same time! Say goodbye when the time is right.

Don’t give your cover crops a complex- They do many things, but they aren’t superheroes; pair cover crops with other weed control and nutrient management techniques to round out your organic gardening methods.

So how do you select and grow cover crops?

Cover crops add organic matter and nitrogen to soil. Since nitrogen is one of the macronutrients plants need to grow and fruit, its presence in good gardening soil is essential. Leguminous cover crops like vetch, clovers or alfalfa all fix nitrogen from the atmosphere into the plant (no fossil fuels necessary). When these legumes decompose their nitrogen is released into the soil profile like a slow release fertilizer for your crops.

Cover crops will prevent nitrogen from leaching out of the soil as well. Non-leguminous cover crops like winter rye, oats and buckwheat are all good at scavenging nitrogen deep in the soil profile before it leaches out. These crops also provide biomass that is converted into organic matter as it decomposes. The organic matter that cover crops provide decreases soil density and improves soil structure. Improvement in these crucial soil characteristics improves soil water holding capacity (good for your plants in a drought), soil nutrient holding capacity (the ‘food’ of the plant world) and tilth (oxygen and structure necessary for healthy roots).

Additionally, cover crops decrease soil erosion by covering the soil thereby protecting it from the effects of wind and rain during the fallow season. They also provide weed control by crowding out other plants anf by limiting seed germination through allelopathy. Allelopathy is the inhibition of other organisms through biochemicals produced by a plant. Cover crops like winter rye have allelopathic properties that can inhibit weed seed germination even after the cover crop has been killed.

The benefits of growing your soil amendments at home are clear, but how do you determine which cover crop to use and when? First, you should establish which garden beds are going be vacant and when. For example, if you have beds that will be used for fall crops or a late crop of tomatoes you can grow the Spring Soil Builder in early spring for a quick heavy growth of legumes and oats. Sow True Seed also provides a mix ready for an end of season niche. You would plant the Fall Soil Builder after a spring or summer crop, particularly a heavy feeder like tomatoes or cabbage. Most Fall cover crops should be established at least 6 weeks before the first frost. The soil builders are premixed to provide a diverse cover crop of legumes in addition to a cereal crop that provides vertical structure for the vining habit of the legumes like vetch or Austrian winter pea.

Another garden niche for cover crops is the summer lull between spring and fall crops. A quick growing cover of buckwheat (6-8 weeks until maturity) would do the trick. Cover crops can also be interseeded (or undersown) with a vegetable crop. The cover crop germinates and grows slowly beneath the vegetable crop, then fills in the space left by the vegetables after harvest. The seed should be irrigated directly after sowing to help germination and pay attention to your garden fertility so that no nutrients are taken from the veggies. Also choose species that will tolerate some shade: white clover, hairy vetch, rye and red clover are suggestions.

In addition, establishing ‘living mulch’ beneath shrubs, trees or perennials is a way to incorporate low input cover crops into your garden. A low growing and shade tolerant species such as Dutch White Clover can become a “living mulch” under trees or other perennials. Again, make sure there is adequate water for your primary crop. And finally, if you are a last minute person, hardy cool season covers like winter rye or Austrian winter pea can be planted pretty late in the season and still establish in time for winter. A thin cover of winter rye planted around the first frost can get a jumpstart in the spring and put on a lot of biomass.

Once you get your cover crop established watch it grow! They are beautiful plants to watch and often they attract wildlife. Buckwheat and the clovers are great for bees! When you are ready to plant your vegetable crop mow or cut down the cover crop at the base of the plants. Let the cover crop material dry on the surface for 1 to 2 days and then turn under or till in the cover crop. Wait two weeks before planting your vegetable crop since the decomposition process will initially tie up nitrogen. An alternate technique is to plant your vegetable starts directly into the cover crop mulch that has been mowed down. The cover crop biomass then can act as mulch for your vegetable crop.

Post & photos by Sow True Seed Blogger Megan Schneider

Sources:

Sarrantonio, Marianne. Northeast Cover Crop Handbook. Rodale Institute, 1994.

Sarrantonio, Marianne. Building soil fertility. From Managing Cover Crops Profitably, 3rd Edition. SARE, 2007 http://www.sare.org/Learning-Center/Books/Managing-Cover-Crops-Profitably-3rd-Edition/Text-Version/Building-Soil-Fertility

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