Under the Cover of Green Manure

We’re all familiar with that wonderful brown substance we call manure, or, as I prefer to call it, “fruit of the butt.” Manure is a rich source of nitrogen for our growing plants, and it can also serve as a mulch. Yes, without manure, life would be pretty sh…, well, you get the idea.

Now, I’d like to introduce you to a different kind of manure. This kind does not come from a bovine or equine backside, but it grows right out of the soil. These are various plants known collectively as cover crops or green manure. Green manure plants are grown for the sole purpose of being killed by cold weather, chopped up, and worked into the soil. Like the other kind of manure, it provides nitrogen, but it does a whole lot more. Green manure crops can crowd out weeds, reduce soil erosion, and improve the overall condition of the soil.

Green manure crops are generally planted in late summer or early fall, then chopped up and worked into the soil in the early spring. Alternatively, they can also be planted in spring or summer, and then tilled into the soil before planting a vegetable crop. They can also be planted in place of a vegetable crop and then worked into the soil to condition it for the following year’s crops.

Green manure crops consist of both legume and non-legume plants. Legumes such as field peas or vetch are planted for their nitrogen-fixing ability while non-legumes – grain crops like rye or wheat are planted for their ability to crowd out weeds. A wide variety of plants can be used as green manure crops. The table below lists some common ones.

The University of Wisconsin Horticulture, Division of Extension gives these instructions for planting. To plant a cover crop or green manure, first clear the planting area of any large stones and other debris.  Rake the area smooth and broadcast seed according to the seeding rate given in Table 1 or as recommended by the seed provider.  Rake the area again to incorporate the seeds into the soil, and lightly water the area. To prevent the cover crop from self-seeding in other areas of your garden, and to utilize the cover crop to its fullest potential, cut down plants when, or just before, they start to flower.  You can cut plants by hand, or by using a trimmer, brush cutter, or mower.  Cutting before flowering not only prevents the cover crop from going to seed, but also stops the plant from taking up nutrients from the soil to store in its seed.  Once plants have been cut, incorporate the plants into the soil (using a shovel, pitch fork or rototiller) where they can more readily decompose.  Allow approximately two to three weeks for the cover crop to decompose before planting your vegetables into the soil. (Source: University of Wisconsin Horticulture, Division of Extension)

So if you are looking for a way to improve the condition of your soil, and the brown manure isn’t doing the job, then why not try the green?

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