Green manures, also known as cover crops, play an important role in organic soil management by ensuring that cultivated land is never left bare, providing bulky green matter to build hummus and general soil fertility, suppressing weeds and lifting and fixing nitrogen. With a little care and planning it is possible to reap the benefits from these wonderful crops all year round.
Our favourite cover crops for the winter
For winter cover we use a mix of annual rye grass and vetch, a combination that both sequesters and fixes nitrogen levels within the soil. This well-known mix is best sown between September and mid-October and germinates fast in the early autumn soil. It provides a rich swathe of hardy green material which can be cut down in February and covered to stop further growth prior to Spring planting. We use a Mountfield lawn mower to ‘cut the grass’ in early February before covering each bed with Mypex for about a month to six weeks. The mix of rye and vetch means that there is root growth at different levels in the soil, which we find really encourages the worms. The cut material also provides bulk to the soil and adds a real boost to overall fertility come spring.
Green manures for spring sowing
As we cut and cover the over-wintered crops in early February we also begin sowing green manures for the spring. Field beans provide a lot of carboniferous bulk for the compost heap as well as fixing nitrogen in the soil if the plants are cut before extensive flowering has occurred. We use field beans on land that has been working particularly hard, for example on beds that have grown very ‘hungry’ plants such as brassicas, as well as on land that we are cultivating for the first time. The leaves and stems are a welcome addition to our spring compost heap and we tend to leave the roots in the ground to encourage microbial life.
In the rest of our market garden beds we sow mustard. This cover crop is fantastic because it is quick to germinate, grows rapidly, provides bulk and weed cover and it is also renowned for cleaning the soil. We cut the plants before flowering and cover the beds for a few weeks before incorporating into the top layer of soil.
Cover crops to boost summer soil fertility
In the summer months, when the beds are almost constantly full and working at their hardest, we use cover crops of either mustard or birdsfoot trefoil in very short cycles to boost soil fertility between successional sowings of salad leaves and other veg. These crops will be allowed to grow for just four weeks before we cut them and start using the beds productively again. We find that this is a fantastic way of resting and reinvigorating the beds during the peak of the growing season. Buckwheat is another alternative that will also work well in this way.
Cover crops benefit wildlife as well as the soil
Green manures have various other uses besides helping to balance and replenish soil health. For example, this year we will be planting Phacelia as part of a wider wildflower sowing plan on newly cleared land in our orchard. Phacelia has beautiful flowers which are pollen-rich and we hope they will support our populations of wild bees and honeybees as the wildflowers begin to establish.
Our favourite cover crop seed suppliers
We are lucky that there are many varieties of organic green manure available in the UK. We buy our seed from Cotswold Seeds and Tamar Seeds and both companies have been excellent, offering great variety and plenty of guidance on their websites.
Learn more about boosting soil health with us
Through our own experiments with cover crops, and learning from trial and error over the years, our advice when it comes to working with these green manures is to keep things simple and give it a go. By including green manures in your annual crop planning you will reap the rewards of healthier soil and better harvests. If you would like to learn more, we explore soil health and the use of green manures in more detail at our sustainable market gardening workshops held here at Wild Garden. Our workshops are limited to small groups to ensure everyone gets a chance to be involved so please book early. We hope to see you there!
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