Green manure crops are a great and easy way to help you increase garden fertility, soil health, and your plant’s health. These crops can also help you increase your garden yields, without increasing input of chemical fertilizers, or expensive purchased fertilizers.
The food that we grow is only as healthy as the soil that it is grown in. The soil feeds the plants and the plants then feed us. If you want to get the most nutrition possible from your garden grown food, it’s best to ensure that it is grown in healthy soil, particularly if you are aiming to grow a family garden.
Adding plants to gardens for use as natural fertilizers, compost, mulch and soil amendments can increase the health of soil and plants without harmful chemicals. It also helps keep gardening input costs lower, and gives you greater control of the lifecycle of your garden.
Nitrogen is a key component in many aspects of plant life such as photosynthesis, protein formation, growth and reproduction. It’s main function is to promote leaf and stem growth, so the plant has enough strength to fruit. Excess nitrogen, however, can be detrimental to root crops, as they prioritize leaves over root creation and nutrient storage. Excess nitrogen in a lettuce or kale bed, however, does wonders.
Nitrogen Fixing Green Manures:
Examples of plants that naturally fix nitrogen in their roots include Beans, Peas, Peanuts, Clover, Vetch, and Fenugreek. These are all legume family plants, and they all form symbiotic relationships with bacteria to fix nitrogen in their root nodes. When using beans and peas in your garden, you can grow them next to other plants that are heavy nitrogen feeders or plant them after heavy feeders the following year to help build the soil back up. The traditional “three sisters” method is one example where beans are planted with corn and squash to help support the two heavier feeding crops with nitrogen.
In order to get the full benefit, it’s very important to leave the roots in the soil after harvest and either till in the top growth as a green manure crop or add it to your compost pile. Beans are also really great at loosening compacted soil because of their extensive root system.
1. Crop Rotation with Peas and Beans:
One of the easiest ways to get the nitrogen fixing benefits of crops like peas and beans is to include them in your crop rotation plants. In a bed that had a high nitrogen drawing plant one year, plant peas or beans the next year. When the peas and beans are done for the season, cut them down and leave them as a winter mulch layer and leave the roots in the soil. In spring, brush whatever plant matter remains on the surface to one side, and plant your next round of crops. A good rotation is root crops, nitrogen fixers, then high draw crops like corn or squash, then leafy veggies, then repeat.
If you want to revitalize a flower bed, then growing sweet peas may be a great way to bring in some extra nitrogen for the next year too.
Peanuts can be grown in growing zone 6 – 11. When harvesting peanuts, the entire plant is typically pulled up and hung to dry for several weeks before removing the peanuts. Once the peanuts are removed, you can return the plant to the garden as a mulch, till it directly into the soil to break down, or add it to your compost pile. Returning spent plants to the garden, either as a mulch or as a tilled in additive, will help increase organic matter and create more porous soil. Plant matter helps to recycle nutrients and improve soil structure and condition. Peanuts encourage beneficial microorganisms and, when used in a planting rotation, help to break disease and pest cycles. Peanuts require minimal water consumption and have deep roots help to break up soil.
Clover is both edible and medicinal and there are many different varieties for different soil types and sun exposure, it is a traditional green manure crop. Different clover types are used for different purposes, red clover is used in traditional herbalism. Clover can be included in a wildflower mix, used as a cover crop in the garden, sown directly into the lawn for bare patches, and planted under fruit-bearing trees or bushes instead of grass. Clover attracts pollinators and other beneficial insects, it improves soil health and helps to stabilize the soil. Clover grows quickly and is often considered a weed when it volunteers. Clover has tap roots and fibrous feeder roots which aerate and loosen the soil, as well as helping fix nitrogen. Clover can help suppress other weeds as well as preventing wind and water erosion when used as a cover crop or on exposed soil banks. Clover is traditionally used as a green manure to add organic matter and nutrients to the soil. It is planted and grown in the autumn and tilled under in the spring. Clover acts as a natural mulch to moderate soil temperatures and reduce evaporation.
American Vetch is a native plant in much of north america and can be used as a green manure, and anti-erosion crop. Vetch is great for erosion control and improves the condition of the soil making it more suitable for planting. Vetch is often used for weed control and can be used for livestock grazing or harvested for forage. It increases crop disease resistance and fixes nitrogen for the crop that follows. Vetch can help reduce runoff and allow more water to penetrate the soil. It also helps to loosen clay soils and is great to mix with clover or grains to increase its passive, beneficial, effects. It is drought tolerant, winter hardy, has vigorous growth and can grow in a variety of soil conditions. Vetch can be used as an organic mulch, cover crop or green manure and is easily killed by cutting close to the ground. Since it is a native to North America, it also helps preserve native pollinators.
Fenugreek is an easy-to-grow annual and aromatic herb, it is not frost hardy. But, it can be grown for it’d edible leaves in zones 4 and above, with a decent chance of producing pods in zones 5+, and year round for leaves and seeds in zones 9-11. It is both edible and medicinal.
Fenugreek is used for food, seasoning, condiments, medicine, topical skin treatments, and livestock forage. It builds the soil and is a great ground cover helping with weed control and moisture retention. Fenugreek can be used as a green manure, if you prefer that to a cut-and-come again green. It can be harvested for leaves, as well as let mature for it’s tasty seeds. It makes an awesome microgreen and sprout. After harvesting the pods you can turn the plants back into the soil or it can be used as a companion plant next to vegetables that are high nitrogen feeders.
Traditional Green Manure Cover Crops
Cover crops are the traditional green manure and a great way to add nitrogen, plant material, and other nutrients back into the soil and help manage weeds, erosion, and nutrient loss. Field peas, annual buckwheat, and rye are some commonly used cover crops.
6. Field Peas:
Field peas can be planted as a cover crop through the winter to keep soil covered and protected. It’s important to cut them down in the spring before they flower. Field peas can keep the soil from hardening, keep nutrients from washing out, and help with weed control. Traditionally, field peas are considered a green manure crop. They are also grown for livestock feed, and some types of field peas are also being used for microgreens now.
Annual buckwheat is not frost or drought-tolerant and doesn’t do well in compacted soil or excessively wet conditions. It grows well in less fertile soil and is great for soil that has been overfarmed or in newly cleared woodland areas. Buckwheat attracts beneficial insects including pollinators and helps to loosen the soil. It grows quickly to help with weed control and also decomposes quickly. If mowed before 25% of the crop has flowered, it will regrow. It can also be tilled in halfway through flowering to reseed for another crop and is a good mid-summer cover crop.
There are white and red flowering buckwheat varieties, and it can provide a field of beautiful flowers for bees if left flowering for long enough. Buckwheat honey is also a valuable item, and has been studied for having similar health and herbal benefits as manukah honey.
8. Winter Rye:
Winter rye is a traditional, European cover crop that helps cycle nutrients back into the soil and improve soil structure. Rye is quick-growing and can tolerate clay and sandy soils. It is drought tolerant and tolerates low soil fertility. Rye is the most winter hardy of all cereal grains but doesn’t do well in excessively wet areas. It can be grown out and harvested as straw for mulch, animal bedding, or mushroom farming. It’s important to harvest before the seeds form. Once harvested it is allowed to dry and then baled for a seed-free mulch. Rye is inexpensive, easy to establish and adds organic matter to the soil. It is a high-quality forage and can also be grown in between row crops to help with wind erosion. Rye is slow to decompose if grown to maturity and can decrease nitrogen availability if tilled in at maturity, as nitrogen is needed to break it down.
For this reason, it is best to incorporate it back into the soil when it’s 12 to 18 inches tall and grow in a mix with legumes to help with nitrogen. Rye is great for weed control because it smothers and out competes the weeds, and releases compounds that inhibit the germination and growth of weeds seeds. If growing next to small-seeded vegetable plants, rye can have the same inhibiting effect. The effect is not noticed if the plants are transplanted into the garden next to rye, rather than directly sown. Rye also improves soil structure, prevents soil erosion, and prevents compacted soils because of its deep root system. Rye can be killed off by mowing, but be sure not to mow too early or it will grow back.
Chop and Drop Green Manures:
Chop and drop fertilizer plants, or chop and drop plants are a useful subset of garden plants. While sometimes invasive in their growing habits, and vigorous in growth in general, they are highly beneficial to return nutrients to the soil. These plants can be cut down and they will continue to grow and produce organic matter and fertilizer for your garden.
Comfrey is an awesome herb, and probably one of the most well-known chop and drop fertilizers. It grows fast. It has a deep tap root, and will regrow from root slips, so plant it where you want it to stay. Native bees love comfrey, so it’s also a great bee plant.
Comfrey contains high levels of nitrogen, phosphorus and potassium which are all essential nutrients for plant growth. It even out-performs composted manure because it is more bioavailable to the plants. You can make mulch, compost and liquid fertilizers from comfrey plants. The deep root system pulls nutrients from the subsoil that is not accessible by most garden plants. It also helps to activate compost when mixed into your compost pile. Comfrey has coarse, scratchy hairs when fully mature, so you will want to be careful when harvesting, or just harvest younger leaves. It is a good idea to wear gloves and long sleeves.
10. Mint Family:
Mint is another great plant to use for the chop and drop method. Did you know that after mint is used to make essential oils, the remaining plant material is often turned into an incredible compost and sold to farmers? This is a great way to make good use of a byproduct of the essential oil process. Mint can be used as a mulch top dressing in the garden and flower beds to help retain moisture, regulate soil temperature, and help with weed control. Mint is high in organic matter and provides lots of micronutrients and it helps to break up hard clay soil for better drainage. Mint also helps deter pests like mice, rats and insects.
Other, more annoying members of the mint family, like stinging nettles, can also be used in this manner. Though maybe making a liquid fertilizer tea out of them might be more pleasant than chopping them down.
While rhubarb is not often used as a chop and drop for the main garden, you can use the rhubarb leaves as an easy and quick mulch. Many people with rhubarb plants use the leaves around the rhubarb itself, but it can be used in other areas or as mulch around bee-garden plants. Rhubarb’s oxalic acid actually helps protect bees from mites, so having a rhubarb near the bee garden can be a great idea.
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This post is a guest post by Tracy McGee
Tracy is the creator, mentor, and teacher at Treasured Creations Homestead. She is passionate about helping families use homesteading skills and natural living to improve their health, deepen their faith, strengthen the family and build community. When she isn’t working on the homestead, you can find her hanging out at the fire station, hiking in the Shawnee National Forest, sitting on the front porch, or taking a road trip with her hubby and kids. Tracy is a member of our DIY Herbal Fellowship, a membership that teaches you how to grow and use herbs for food and medicine.