Green manure is a great way of adding nutrients to your soil and supressing weed growth. It is popular in organic agriculture as it avoids the need for chemical fertilisers. Green manure helps to build soil fertility as well as maintaining soil structure.
What Is Green Manure?
Green manure is a crop that you plant and then turn into the soil while it is still green. Some are be planted in Autumn and will grow over winter. Dig them into the soil in spring ready to plant a food crop. Others are allowed to grow over a full growing season as part of a crop rotation. The following year, dig it into the soil, and plant a food crop.
What Are The Benefits Of Using Green Manure?
There are several benefits of green manure. It adds organic matter and nutrients to the soil when they are dug in. They also act as a cover crop while growing. Cover crops supress the growth of weeds in the soil and reduce soil compaction from rain.
Some green manure cover crops attract pollinators, which are a great benefit for your garden. The cover crops provide protection for beetles, another beneficial insect.
Are There Any Drawbacks To Using Green Manure?
Although the use of green manure does bring a lot of benefits, there are minor drawbacks too.
Diseases and pests can survive over winter if there is a cover crop, known as creating a green bridge. To avoid it, choose varieties that won’t support diseases or pests that affect the following crop. Select a green manure from a different type of plant family instead. For example, don’t use a legume followed by a legume vegetable crop.
A green over winter ground cover attracts slugs and snails. Make sure that you provide adequate protection from them.
What Are The Best Plants To Use As Green Manure?
The best plant to choose for green manure depends on when you want to grow it. Some will grow well over winter, while others need warm conditions. Different green manure plants bring different benefits too.
The best green manure plants are:
- Red Clover
- Field Beans
- Grazing Rye
Below are additional details of each of these varieties.
Alfafa is a legume that grows well when sown in spring or summer. Sow seeds between April and July. Ready to dig in to the soil after 2-3 months or you can leave it for up to two years.
Clover is a fast growing legume. There are many different varieties of clover, with red clover being the best for nitrogen fixing. It produces a large amount of foliage, so is great for supressing weeds. Sow between April and September, works well as a winter cover crop. Ready to dig in to the soil after 2-3 months, or you can leave it for a year.
Field beans (same species as broad or fava beans) are another member of the legume family. This is great for growing over-winter, and a good nitrogen fixer too. Often grown in combination with grazing rye to further supress weeds. Sow between September and November and dig in to the soil two or three months later.
Grazing (or forage) rye is a cereal rye that is one of the best over-wintering green manures. It has deep roots that improve soil structure and lift nitrogen in the soil. Its foliage is think and great for supressing weeds. Often planted in combination with field beans. Sow between August and October and dig in the following Spring.
Mustard is a member of the brassica family. It produces a lot of foliage and fibre, which is good for soil that doesn’t have a lot of organic matter. Sow between March and September, and dig in after two or three months.
Buckwheat is in a plant family of its own, so you can plant any crop after it. It germinates easily and grows well, even in poor soils. Buckwheat’s dense foliage is great at supressing weeds. Sow between May and August and dig in two to three months later.
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