Green manure has long been an essential part of organic farming. It is a type of cover crop that is grown primarily to add nutrients and organic matter to the soil. However, some of the plants used in this type of manure are often beautiful and decorative in their own right and when used in the garden or on the vegetable patch, are not only beneficial to the soil but can also provide us with an inspirational show of colour.
Why use green manure?
There are many reasons why we might want to use green manure in our gardens or allotments. Some add a dose of nitrogen to the soil by taking it from the air and making it available in the soil for the following crop. It also suppresses weeds and helps retain soil moisture. Many of the plants used root deeply and so help to break up the soil and aerate it. They also attract beneficial insects that promote pollination or feed on unwanted pests. Finally, once they finish flowering their foliage can be dug into the ground to improve the soil structure or composted.
How to grow green manure
Growing green manure couldn’t be easier. Prepare the ground to a fine tilth and then broadcast the seed directly on to it. Lightly rake over and leave the seed undisturbed to germinate and grow. The advantage of using this type of manure is that many of the plants only last for around three months and so can be used as temporary space fillers to be cut down and dug in once they have gone over. There are basically two types of green manures – those that are suited to overwintering, and those more suited to growing through the summer months.
Winter green manures
Overwintering green manures are often not as attractive as those grown in the summer months but they are invaluable to protecting and enriching the soil during the long months of winter. Crimson clover fixes nitrogen into the soil and has lovely crimson flowers during summer. Sow between April and August. Field beans also add nitrogen to the soil and provide fast-growing winter cover if sown between September and November. Alfalfa draws up minerals and nutrients from the subsoil while also fixing nitrogen from the air. Sow this between May and July.
Summer green manures
Many of the plants used in summer green manures are extremely attractive in their own right and can even be grown in amongst flower beds, providing colour as well as helping to retain soil moisture and providing nutrients. Phacelia is probably the most attractive and is often mistaken for lavender. Its flowers draw beneficial insects. Sow between March and September. Agricultural lupins are very deep rooting and so break up heavy soils as well as having beautiful insect-attracting flowers. Sow them between March and June. White clover is a low growing nitrogen fixer whose white flowers attract pollinating insects. Sow between April and August. If you really don’t have the space to grow large amounts of green manure, then why not grow summer green manures in garden planters. Not only will it provide you will a show of colour but you can add it to the compost heap after flowering knowing that it will be doing its bit to improve your soil for next season.