Grow your own manure

Growing a green manure on vacant soil after the crops have been harvested is a brilliant, traditional, organic method of improving your soil. They will add organic matter, help retain nutrients, help suppress weeds and in the case of leguminous green manures will actually increase the amount of nitrogen in the soil for the following crop. This is an ideal time of year to sow clovers and grazing rye to dig in during early spring. Or, on heavy soils, try buckwheat or fenugreek to dig in after the first frosts but before the winter rains.

Why grow green manures?

• Help suppress weeds
• Add organic matter to the soil
• Help open up heavy soils
• Increase available nutrients
• Protect bare soil from ‘capping’ in heavy rain

Making the most of green manures couldn’t be easier. Just rake the soil level, sow the seed, let it grow and dig it in. The incorporated green plant matter will break down, releasing nutrients over a period of time, so that the follow-on crops never run short. The main problem with green manures is that they are only really a practical option for parts of the garden that are left vacant for periods of time, notably the vegetable plot. But they could be used as a way of preparing the ground for a new lawn or as a ‘filler’ to cover the ground in a new garden while you decide on the design.

Choosing a green manure Which variety you choose should depend on the window of opportunity you have to grow it. Select one that can be sown as soon as the ground becomes vacant and then dug in before the ground is needed again. I have already mentioned three types that can be sown at this time of the year, but if the ground becomes vacant during spring, alfalfa, lupin or mustard would be good choices. Then for autumn sowings, winter field beans and winter tares can be used. On the vegetable plot, you will need to bear in mind the crop rotation when choosing your green manure. For example, you would not want to grow leguminous green manures, such as clover, fenugreek and lupin, on ground destined for peas and beans because of potential carry-over of pest and disease problems. Clubroot-susceptible mustard should be avoided on soil infected with this debilitating disease.

If the window of opportunity is short, it might still be worthwhile sowing a green manure, because they can be dug in at any stage – even as seedlings. Obviously the more green material they generate the more value they are to the soil. But bear in mind the taller and tougher the stems, the more difficult they will be to dig in. My big tip here is to make sure you dig them in before they flower, so that they don’t have a chance to set seed and become a weed problem in the future. If you are leaving soil vacant for a long time, you would be better off sowing two or three crops of green manure and digging them in young, than letting one crop get old and woody before it is incorporated. Alternatively, perennial green manures like alfalfa and clover, could simply be chopped down to ground level two or three times a year to prevent them flowering and encourage further flushes of new growth.

Planting afterwards It doesn’t take long for the soft-green growth to break down in the soil during the growing season, so you can start planting after a week or two. At other times of year and if the green manure has been allowed to get more mature before digging in, you may have to wait twice as long as this before planting the follow-on crop.