Understanding Cover Crops and Green Manure Crops

Last year, when I decided to become a market gardener, I automatically assumed that the best thing will be to just expand my current operation. So I set up my 66 garden beds on our farm and after preparing the soil I covered the whole thing with many bales of hay that cost me a good amount of money.

I soon realized what a huge mistake I made. It was impossible to do the work with so much hay everywhere. I couldn’t use a seeder, the weeds that did come through the hay took me hours to clean (since I couldn’t use a hoe), and at harvest time the hay was constantly in my way and I had to spend hours cleaning my harvest so I don’t go to market with bags of lettuce mix full of hay in them.

I am not saying it’s not possible to farm on a larger scale with hay as ground cover, it probably is, but I felt like for me it was too expensive and time-consuming.

However, since I still believe in not leaving soil bare, I started researching other alternatives, something that will work on a larger scale.

I’ve heard about cover crops and green manures before, but never dug deep since my home garden space is so small and I was doing great with the hay as mulch. I started researching a while ago and to tell you the truth I was a bit overwhelmed with the amount of information, practices, the number of cover crops available and so on. I experimented a little bit with planting buckwheat, but it was a disaster…

So I am writing this for you and for myself. I am going to organize this whole cover crops topic in my head so when the time comes I can put together a simple plan that will (hopefully) work at my farm, and I thought I’ll share it with you in case you want to try using cover crops in your garden as well.

I want to emphasize that you don’t have to be a farmer to use cover crops. You can incorporate cover crops in any size garden, you’ll soon see how they can benefit even your small-scale vegetable production.

What are Cover Crops and Green Manure Crops?

Cover crops and green manure crops are crops we grow to improve the soil. They usually aren’t used to pasture livestock (although there are some exceptions) and aren’t sold as cash crops.

Green manure crops are cover crops we plant with the intention of incorporating (usually by tilling) them into the soil while the plant is still green and before it sets seeds.

A cover crop, on the other hand, can be mowed and incorporated (or not, we will talk about this later) into the soil at any stage.

So whether a crop is a cover crop or a green manure crop depends on how a farmer is going to use it rather than which specific crop it is. Is he going to leave it to cover the ground for a long period of time? Or is he going to till it under while it’s still green?

To make it easy on all of us, I am going to use the term cover crop through this post since it’s a bit broader.

Benefits of Cover Crops –

Prevent Erosion – the USDA explains erosion as the breakdown, detachment, transport, and redistribution of soil particles by forces of water, wind, or gravity. Soil erosion on cropland is of particular interest because of its on-site impacts on soil quality and crop productivity, and its off-site impacts on water quantity and quality, air quality, and biological activity. Cropland includes cultivated and non-cultivated cropland.

Even though rates of erosion declined in the past few years we are still losing about 1.7 billion tons of topsoil to erosion every year.

Roots of cover crops hold the soil together and help protect it from water erosion. The upper part of the plants covers the soil and prevents winds from carrying away dry topsoil.

Prevent the Loss of Nutrients – nutrients in the topsoil can be lost to erosion, however, this is not the only way nutrients can be lost. They can also leach down bellow plants root level what makes them unavailable for plants. Cover crops, or in this case they can also be called catch crops, capture and hold those nutrients.

When they die and decompose, those nutrients are returned to the top level of the soil.

This process also helps keep our water sources clean. Access nitrogen, phosphorus, and other plant nutrients (even though natural) can have a negative effect on water if they leach into ponds, rivers, lakes, and streams. Catch crops hold access nutrients in the soil.

Add Organic Matter to the Soil – at some point, cover crops are tilled back into the soil or mowed and left on the soil to decompose. Once they break down, they add a great amount of organic matter to the soil. In addition, they provide a great amount of food for the trillions of organisms that live in the soil.

Add Nitrogen and Cut Fertilizer Costs – this is another good reason to use cover crops. Last year, I bought a few bags of organic fertilizer and learned just how expensive it is. If you have a large garden, or if you farm a few acres, it adds up to a lot of money.

Leguminous cover crops (clover, beans, peas, vetch, soybeans, and alfalfa, for example) have the ability to capture nitrogen from the atmosphere and store it in nodules in their roots. Once those plants die and decompose, they release nitrogen back into the soil. This nitrogen is easily available and very valuable for the subsequent crops (although it might be tied up by soil microbes for a while. When those microbes die, they release the nitrogen. This precess will move along faster in warm, moist soil).

So, by using leguminous cover crops, and because cover crops, when decomposed, add so much organic matter to the soil, they can significantly reduce or even eliminate the need to purchase organic fertilizers and compost.

Suppress Weeds – some cover crops are very good at suppressing weeds. Some crops grow very fast and pretty much monopolize the supply of nutrients, water, and sunlight.

Other cover crops (winter rye, oats, sorghum, and sudangrass) produce toxic compounds that prevent other seeds from germinating and slowing the growth of nearby plants. This is called ‘allelopathy’. Keep in mind that those cover crops affect vegetables just as much as they affect other plants, so waiting a few weeks (3 or so) before planting after tilling under those crops is a good idea.

Break Up Compacted Soil – some cover crops are very deep-rooted. Thier roots are capable of penetrating deep into subsoil levels, breaking up dense layers.

Another advantage here is that those cover crops reach nutrients and minerals cash crops can’t reach. Those minerals and nutrients become available to other crops once the cover crop decompose.

Attract Beneficial Insects and Fight Pests – many cover crops, especially the ones that flower (clover, buckwheat, for example), provide habitat for beneficial insects. Those, can not only fight pests but also help with pollination.

Next in this post is an overview of the methods you can use to incorporate cover crops in your garden, a list of the most common cover crops, how to choose the right crop for your garden, and a few videos that will help you understand how farmers use cover crops. make sure to click on the link bellow to keep reading.