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Chop and change: transforming your soil with green manure


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Mar 21, 2024
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Chop and change: transforming your soil with green manure

If you’re an enthusiastic veg grower or even a beginner keen to get the most from your plot, you might be looking for ways to increase your yield. Healthy soil is key to a bumper crop and one of the best ways of improving it is to use a green manure.

So what is it? A green manure is a fast-growing crop sown on bare soil that acts as a natural fertiliser. Once mature, it’s cut and either dug in or left on the soil surface to naturally work its way in.

Adding organic matter in this way is particularly useful for vegetable patches and allotments as many veg are hungry crops, demanding high levels of nutrients in return for providing food for their growers. It’s also a good start for a completely new garden in a plot where the soil may be poor as a result of overcultivation or compaction.

As well as boosting fertility, green manures improve soil structure, adding drainage in areas that are too wet and increasing water retention in dry periods. Given our increasingly unpredictable climate, having this sort of insurance to fall back on can only be a good thing! Many are also nitrogen fixers, taking nitrogen (an important plant nutrient) from the air and storing it in nodules in their roots.

They can be used to prepare a whole area for planting or simply as catch crops to cover bare areas between, for example, rows of sweet corn, or in the space left after potatoes have been dug up.

Green manures have other benefits too. Diligent horticultural multi-taskers, they also:

  • Help to suppress weeds.

  • Help to prevent soil and valuable nutrients from washing away in heavy rains.

  • Provide habitats for beneficial insects such as ground beetles.

Some, like buckwheat, clover and bitter blue lupin will, if you leave them in place for long enough, develop into a sort of mini-meadow, producing a dainty or (in the case of purple tansy) rather spectacular display of flowers. As well as their visual appeal they’re an absolute magnet for bees, hoverflies and other pollinators, for whom they’re a valuable source of pollen and nectar.

All green manures prefer an open, sunny spot.

What’s the process?

Weed your chosen area thoroughly, then sow your seeds according to the instructions on the pack and wait for them to grow. When mature, chop off the foliage and leave it on the soil surface for a couple of days to wilt down. Then turn over the soil to unearth the roots, digging all the plant material into the top 20cm or so of soil.

After this, wait for at least two weeks before planting or at least four weeks before sowing the seeds of vegetables and other plants. This will allow the green manure to break down and begin to do its work releasing nutrients into the soil. It’s also because the material, while it’s decaying, can hinder rather than help the growth of new plants.

You can see Monty Don sowing grazing rye here:

Complete Guide to Green Manures | BBC Gardeners World Magazine

For fans of no-dig gardening, ‘chop and drop’ is an alternative to digging in. Simply cut down the plant material in autumn and allow it to decay on the soil surface, working its way in over winter with the help of rain and worms and other invertebrates.

You’ll know it’s time to cut your manure crop when the flowering plants start to produce blooms. Grasses such as rye develop a flower bud in the centre of the plant which you should be able to feel with your fingers.

To bring in the pollinators, leave flowering plants until they start to set seed. The disadvantage of this is that individual blooms, of course, mature over a period of time rather than all at once. So it’s almost inevitable that some seeds will be dug back into the ground to pop up again the following year. You may not mind this (the pollinators certainly won’t), but it’s something to be taken into consideration, depending on what you have in mind for the future. Be mindful too that woodier growth (from mature flower stems) takes longer to decompose.

Choosing your seeds

One of the wonderful things about green manures is that, like all plants, they have differing needs so suit a variety of conditions and can be used for a range of purposes.

For overwintering: sow hardy manures in late summer or autumn and dig in during early spring. Try leguminous Essex red clover (Trifolium pratense), winter field beans (Vicia faba) and winter tares (Vicia sativa).

As a catch crop: low-growing, fast-maturing plants such as mustard (Sinapis alba) and clovers.

On light, dry and alkaline soils: leguminous black medick (Medicago lupulina) or alfalfa (Medicago sativa) which has purple, clover-like flowers.

On wet, acidic soils: alsike clover (Trifolium hybridum).

To break up heavy clay soils: grazing rye (Secale cereale).

To attract pollinators: purple tansy (Phacelia tanacetifolia), clovers, buckwheat (Fagopyrum esculentum) and bitter blue lupin (Lupinus angustifolius).

These seeds may not be available in all our stores but do ask our staff for help. They may be able order some for you or suggest alternatives.

Grower beware – potential hiccups:

  • Mustard is a member of the brassica family, which is prone to clubroot, a disease affecting vegetables such cabbages, cauliflower and swedes. It’s wise, therefore, not to follow mustard with these plants and to use crop rotation to avoid possible problems.

  • A thick layer of plant material is the perfect place for slugs and snails to lurk, particularly if you’re using the chop and drop method. These fiendish molluscs love large leaves so chopping finely will help.

For more details of planting and maturation times:



Many green manures can be dug in after two and a half to three months, so if sown now should slot nicely into the timetable for planting out tender crops such as tomatoes, courgettes and runner beans in early summer. Nature, as we know, abhors a vacuum and in horticultural terms this means that weeds will seize the opportunity to spring up on any patch of bare ground they find. The trouble with weeds is that they steal some of the nutrients from the soil without giving anything to the gardener in return. So why not plant a green manure instead and reap the rewards?


The post Chop and change: transforming your soil with green manure appeared first on Capital Gardens.
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