What is a Cover Crop? A breakdown of "green manure" and what it can do for your garden.

Many of us growers are familiar with the concept of amending soil. Adding compost annually or even twice annually increases the amount of organic matter. In other words, it gives us new and more soil to work with. Added compost improves soil tilth, contributes nutrients (which eventually liquefy and become readily accessible to the plant over time), and increases all that good bacteria and protozoa which contributes to the greater mycorrhiza network. Good soil, in short, results in healthy plants.

Strong, thriving plants are able to not only produce more nutrient-dense food but are also able to better protect themselves from pests and even some forms of disease. Did you know that a healthy tomato plant, for example, can release enzymes into its leaves when it detects caterpillars are eating its foliage? The enzymes are intense—they influence the caterpillars to eat their own kind, rather than feast on the tomato leaves. The caterpillars become cannibals and leave the plant alone. It’s true! Wild, right? But a tomato plant can’t perform this mind-blowing function if it’s not healthy enough to do so. And that’s where soil health comes in.

​I add compost to my growing spaces every year but I also started working with cover crops. Cover crops are the “green manures” of the plant world for the nutrients they add to the soil. Just like amendments, cover crops can contribute all sorts of benefits to the Earth. These crops aren’t grown for us to harvest and eat but rather they complete their entire lifecycle within the soil. They are planted for the sole benefit of soil enhancement. Some cover crops add nitrogen like vetch or clover. Other cover crops help to loosen compacted soils like field turnip or radish. Cover crops can be mixed to achieve multiple functions and reap maximum benefit like increasing nutrients, attracting or harboring beneficial insects, reducing erosion, making nutrients more soluble, and the list goes on.

Cover Crops in the Pasture
When I learned about all of these efficient perks I asked myself, “Why grow grass in my grazing pastures when all that really does is prevent erosion? Why not gain more function and try forageable cover crops?”
​
I started researching cover crops that could feed my animals and my soil at the same time. This became my introduction to sowing green manures. My plot of land is rich in weeds, clay soil, is prone to horrible erosion, and lacks nutrients. I also keep horses, sheep, and a flock of ducks, geese, and guinea fowl. I decided to research and cross-reference those findings to find a cover crop mix that would solve both my soil challenges and meet the nutritional needs of my animals. It sounded like a tall order but I was surprised to learn it wasn’t all that difficult to achieve. I found this table by the Rodale Institute to be a total game changer and I still reference it regularly.

After selecting which cover crops I wanted to grow based on their soil contributions, I started research on animal compatibility. I learned quickly that some cover crops are suitable for grazing specific species while others aren’t. Piper Sudan Grass is a great option but contains high amounts of Prussic Acid, specifically in the morning, which can be detrimental to the health of horses. Certain types of clover are more prone to hosting a mycotoxin that causes salivation in horses. Finally I decided on a mix of triticale, annual rye, forage turnip, and Berseem clover for my fields. All would help my soil and feed my animals.
​
For a few years I sowed my cover crops in early spring and late summer. Soil health does not improve instantaneously but rather takes years. My animals happily grazed the crops, and the soil little by little visibly seems darker, richer, and able to hold more water. If I could escalate the health and porosity of my compacted pastures, surely I could use them in my vegetable garden as well?

Cover Crops in the Garden
Permaculture and sustainable growers recognize the importance of keeping soils covered all the time, all year long. Mulches come in many forms such as tree leaves, straw, woodchips, chopped hemp, and more. These coverings help to retain moisture, suppress weeds, reduce erosion, keep absorbed carbon within the soil, and prevent the nutrients and beneficial bacteria that reside there from being cooked off by the sun. Cover crops not only perform all of these but as living mulches they attract beneficial insects, maintain the mycorrhiza fungi network during the off-season with their living roots, and add even more nutrients to the soil. Just like I did with my pasture spaces, I chose to focus on specific challenges and use cover crops to address those. I now sow a blend that I created which contains hairy vetch, field pea, crimson clover, and triticale. This mix is suitable for my central New Jersey zone 7a climate, stays green during our cold winters, and performs the following:

• harbors beneficial insects
• takes up and holds soluble nitrogen
• adds nitrogen
• makes soil phosphorous more available
• suppresses weeds
• improves topsoil health

I sowed this mix in the garden in October, in areas where our vegetable crops were done for the season. It eagerly sprouted and remained green all winter long. In the spring when I was ready to use the beds once again for planting, I simply chopped and dropped the cover crops in place. Using my hands I pulled the stems just at the soil line, leaving the roots. The green foliage in my hand was simply dropped on top of the soil and left to decompose. I then interplanted crops between the remaining roots of the cover crop. I’ve also used rabbits to forage down the cover crop with a chicken-tractor-style contraption called A Bun Run. You can find that info and video here. Though I’ve only been using cover crops in my vegetable growing plots for a short time, I can see the soil is darker and richer.
​
To summarize, cover crops are plants we grow for the soil. A wide variety of cover crops can be chosen to perform a wide variety of tasks. There’s an excellent book by Gabe Brown called Dirt to Soil, and he’s a huge proponent of growing as many cover crops in once area as possible. I highly recommend this book along with the research and easy-to-use chart published by Rodale Institute if you’re hoping to improve your soil quality. I also have a chapter in my book, The Sustainable Homestead, dedicated to pastures which references cover crop-animal species compatibility. It may sound intimidating at first but just like we select crops to grow for their yields or flavor, we can select green manure for their individual functions too. Thanks for reading!