September 21, 2013

Cover Crops in the Fall Garden

I have three species of cover crop growing in my garden right now.  I like growing winter cover crops rather than just covering the garden with leaf mulch for several reasons:
  • Grassy cover crops grow extensive root systems that protect the soil from erosion.
  • The plants uptake soil nutrients that otherwise would be lost to leaching.
  • They inhibit weeds.
  • The tall cover grasses increase soil moisture by trapping snow and shading the soil.
  • Legume species produce their own nitrogen fertilizer.
  • Cover crops increase levels of organic material in the soil.
  • They're cheaper and easier than hauling in manure or compost and serve the same functions.
  • I like looking out my window in mid-winter and seeing plants in my garden!
A well-established bed of rye and vetch sown after the potatoes were harvested.
I've sown winter rye and hairy vetch in most areas where I've pulled out the summer vegetables.  Rye and vetch are the most winter hardy cover crops for New England and will grow until the deep cold of January and February.  Vigorous growth will resume in the spring.  The spring growth will produce an amazing amount of biomass from the rye, and the vetch (a legume) will increase the fertility of the soil through nitrogen fixation.  The rye/vetch mix will have to be mown and tilled under in the spring.  The major drawback of rye is that the residues will inhibit the growth of other plants for at least three weeks after tilling in the rye.

Rye and vetch sprouting beneath the fall lettuce patch.
The tomatoes, peppers, and eggplant were undersown with oats around mid-July to provide a living mulch.  I'll pull these veggies once the first frost hits, leaving behind a well-established oat cover crop. The oats will die over the winter and leave a nice mulch on the soil to protect against runoff during the spring rains.  I can either plant spring crops directly through the mulch or till it under.  Similarly, I planted rye and vetch beneath some of the fall veggies like lettuce to let the cover crops get a head start.  I typically plant the winter cover crops no later than the second week of September; any later and the tender young plants will not fare well against the early frosts.

Oats were sown beneath the tomatoes in mid-July.
Next year I will experiment with more mid-season undersown cover crops using legumes such as dwarf white clover.  The clover will act as a living mulch that should reduce the slug problems I had this year using leaf mulch beneath the plants. 

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