Planting Green Manure
This link to planting green manure arises out of an event to mark 2015 as UN International Year of the Soil, an event that we are contributing to in Bristol, UK through July and August 2015. This event, Soil Culture at CREATE, is a celebration, consciousness-raising, community building event that puts the importance of soil stewardship at the fore.
If you came away from Soil Culture at CREATE with some seeds and want to know more about how to work with them these pages are for you.
If you didn’t attend the Soil event but want to work with Green Manure for enhancing your soil, this page is also for you! You can often find these seeds from a search online or from local gardening suppliers. We do recommend that you get organic seed.
These plants are known as ‘green manure’ plants or ‘cover crop’ plants. They are often not sown for harvest (they don’t produce large fruits or tubers, for instance) but are ‘turned in’ to the soil at a certain stage of growth so that they can be re-incorporated in the soil.
There are a number of commonly used green manure crops such as
- Mustard – Sinapis alba,
- Phacelia – Phacelia tanacetifolia and
- Clover – Trifolium sp
Seeds from Soil Culture at CREATE
If you are looking to identify seeds, particularly those who picked seeds up in Bristol, the following images might help.
The Benefits of Planting Green Manures and Incorporating Them in Your Soil
There are a number of benefits to planting green manure crops, cutting them before they go into seed and digging them into the soil to decompose. Some of these benefits are:
- As green manures or cover crops decompose there is an increase in soil microorganisms that multiply in order to breakdown the plant matter. This breakdown releases nutrients previously held within the plants to be available for later plantings of crops.
- Nutrients that are released through decomposition include sulfur (S), potassium (K), calcium (Ca), phosphorus (P), magnesium (Mg).
- Nitrogen fixing – legumes (clover, vetch, tarres) store nitrogen (N) in nodules in their roots. This nitrogen is made available to the soil and soil organisms as the plants decompose.
- Some deep-rooting green manure crops (rye grass for instance) contribute to the development of good soil structure, their deep roots break up soil and draw up nutrients from layers of the soil that shallower-rooted plants can’t access.
- Green manures ensure good cover of soil between plantings of other crops, helping slow or stop the loss of nutrients that can occur when ground is left bare or exposed.
- Cover crops and green manures suppress unwanted growth (weeds) and encourage beneficial insects.
How to Plant Your Green Manure Seeds
- Remove any unwanted plants from the area you wish to cultivate and sow with green manure crops.
- Scatter seeds evenly over the prepared ground and gently tamp the seeds in with the back of a spade, do not dig in larger seeds (such as broad beans).
- Water the seed in and keep the seed moist until it has sprouted and produced and upright shoot.
- If there are obvious bare patches after this first planting, sow more seeds in the gaps after a few days. Water these in well.
- Before the plants begin to flower, cut them and chop them up with a spade, lightly digging them in. If this is done four weeks before planting or transplanting vegetables then the green manure will have had time to break down.
- Green manures can be planted early in beds that are going to receive transplants and cut in advance of the transplant, and should be sown when a bed or field is going to be left bare after harvest, such as over the winter.
There are a number of good resources if you want to know more about working with green manures.
- You can watch several short videos on planting and incorporating green manures on https://www.greenmanure.co.uk/pages/green-manure-videos
- Gardener’s World also has a video on their website about green manuring, which you can watch here
- Most books on Organic Gardening, Permaculture and natural farming will have sections on Green manure and Cover Crops.
Happy planting !