“Green manure” refers to plants that are grown to improve the soil rather than for eating or for their aesthetic qualities. Many farmers and gardeners work livestock manure into their plots before planting to supply essential nutrients to their crops and increase the vitality of the soil. Green manure plants serve the same function, allowing you to give your garden crops a valuable boost with no need for you to shovel out a barn.
What Are Green Manure Plants
Cover crops, another name for green manure, are planted during the off-season when your garden is not producing food or flowers. Green manure plants typically are legumes, such as crimson clover and hairy vetch, or grasses like buckwheat and oats. There are lots of options to pick from, and the right choices depend on your geographical region, when you want to plant them, and what your goals are. The Old Farmer’s Almanac has a handy guide to help you choose the best green manure plants for your garden.
How Does Green Manure Benefit the Garden?
Why should you use your garden space to grow plants that you don’t eat? Green manure crops help your garden become healthier and more productive in a variety of ways.
Enriches Soil
When green manure plants reach their mature size, they’re turned into the soil while still green or after they’ve died back, depending on the type. As the stems, leaves, and roots decompose, they become organic matter that nourishes earthworms and all the other beneficial organisms in the soil. Many types of legume cover crops also “fix” nitrogen, a key plant nutrient, by extracting it from the air and releasing it into the soil.
Enhances Soil Tilth
“Tilth” is a description of the soil’s physical conditions. That is, how hard or loose it is, how well it holds water, and what is its mineral content. When green manure plants sink their roots deep into the earth, they improve the tilth by aerating the soil, increasing water, root, and air penetration, and pulling minerals from down in the subsoil into the topsoil. The decomposing organic matter from green manure helps sandy soils retain moisture and improves drainage in heavy clay soils.
Controls Weeds
Cover crops can function as a living mulch, shading and crowding out weeds before they grow in your garden. Many experienced growers today knock down green manures rather than turning them into the soil. Their stems form a thick, natural mat on top of the ground that obstructs weeds and then gradually decomposes into the soil.
Supports Soil Food Web
Your garden plants’ health depends on a robust population of insects, fungi, and bacteria. They digest the organic matter and release it as nutrients that plants can absorb. These beneficial organisms also protect your garden plants by fending off diseases and harmful microbes in the soil. Supplying organic matter nourishes the whole, interconnected soil food web.
Prevents Soil Erosion
Bare ground in your garden is vulnerable to erosion from heavy rainfall and winds. The roots of green manure crops hold the soil in place when you don’t have any crops growing in your garden. Cover crops also reduce stormwater runoff by keeping the soil loose and rapidly absorbing excess rainfall.
Attracts Pollinators
Many types of cover crops, such as red clover and buckwheat, bear flowers that attract bees, moths, and other pollinators to your garden. Keeping these creatures around your plot increases your harvest when you are growing crops to eat. What’s more, filling an otherwise bare garden with green manure crops also creates a habitat for many species of birds, insects, and small mammals.
Building healthy soil is one of the keys to gardening success. Green manure crops can be a valuable aid, helping you to maximize the harvest and satisfaction you get from your garden.
Find out more about improving your garden soil with When and How to Amend Soil.