Tuesday, November 13, 2012

Sow Cover Crops for a Healthier Soil

Photo from Vintage Garden Gal
Now that you pulled all the summer veggies, and hopefully put them in your compost pile, it is time to think about feeding the soil.  Your soil has been depleted by the fast growing summer vegetables and if you don't plan on growing any winter vegetables, instead of leaving your beds empty consider planting them with a cover crop.

Cover crops or green manure are a fast and cheap way to add nitrogen and organic matter to your soil.   Cover crops have been used for centuries to replenish the fertility of soil.  If you want more information than I am providing here visit this great guide from Cornell University, which is targeted more to growers but has a nice extensive list of plants used as cover crops.  Sadly it advises to kill the cover crops with an herbicide before tilling it in, wrong!

Photo courtesy of Mother Earth News
Winter or cool season cover crops are normally planted in the Fall, and albeit it is a little late for some cold winter regions, if you live in California you can still throw some seeds on the ground for a nice spring harvest.

Cover crops can have three functions, enrich the soil of nitrogen, increase the biomass of organic matter in your soil, and when harvested they can be added to your compost pile to work as a green manure. 

There are two types of winter cover crop, the nitrogen fixing legumes, and the grasses like rye.  Plants in the legume family add nitrogen to the soil through the actions of bacteria present in nodules on their roots.  Without getting too technical, the bacteria absorb the nitrogen present in the air, in a gas form, and transform it or "fix" it into a form that is absorbed by plants.   When the plant is harvested and the roots left in the soil, the nodules degrade and the fixed nitrogen is releases into the soil.  Cool season legumes include clover, vetch, alfalfa, and fava beans.  

Photo courtesy of KB seed solutions
Grasses and grains build the soil and boost fertility by adding organic material and loosening hard soil with their long roots, they also suppress weeds and control erosion.  Annual ryegrass, barley and oats are commonly used.

Depending on your particular soil situation you can use one type of cover crop or a combination if you want your cover crop to accomplish more than one of the above.  If you are unable to find cover crop seeds at some of your local nurseries you can find them online.  Bountiful Gardens offers cover crop seeds in bulk, while Peaceful Valley Farm & Garden Supply has many soil building cover crop blends.

Once you have your seeds, remove and compost any debry of the spent summer vegetables.  Loosen the soil with a spade, breaking any hard clumps, rake it smooth and spread the seeds according to the packet instruction (if you plant too many you can always thin them later).  Gently rake the seeds into the soil and cover with some straw.  Water well for the first week or so.  Once the seedling emerge you can water less, or not at all if you have plenty of rain.

It is very important to harvest the legume plants right when they start flowering, which depends on the region you live in, it could be as early as February.  Once the plant start flowering it starts using the nitrogen present in the nodules to produce its own seeds so for maximum nitrogen crop plants need to be cut down at the first blooming.  Depending on how depleted your soil is you can either cut down the whole plant and till it in the soil, or cut and compost the green part and leave the roots to decompose in the soil.  If you leave the whole plant in, cut it in smaller pieces, till it in the soil and cover it so the soil microorganisms will decompose it faster.  In two or four weeks you can follow it with your spring planting.  For grass crops the harvesting is less critical but plan on cutting the plants when they are six to eight inches tall and till them in at least a month before you plan on using the bed.  If the grasses are left too long they get more woody and will take a longer time to decompose.

Happy Gardening!