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Sowing green manures
14 Jul

Sowing green manures

Posted By: rocket veg Category: Seasonal Tips

I’ve been mostly sowing ‘green manures’ this week, so if like me you have a patch of ground which has yielded up this year’s crop - and if you have never planted green manures before - read on.

Protect your soil

At several points in the year, an allotment or veg patch will have bare soil where crops once grew and which is now being rested. If you are new to the delights of veg growing, you will have quickly realised that weeds are very adept at taking over uncultivated ground and before you know it, what was beautiful soil in pristine condition has become a weed-infested jungle! There are two ways to avoid weeds getting a hold: covering with a suitable material which blocks out light but allows rainwater to filter through; or putting the patch of ground to use again. I am a big fan of the former method during winter months when little will grow and I want to protect the soil structure from the ravages of harsh weather, at the same time encouraging worm activity. During the summer months, I generally sow a variety of green manures on at least one large patch of my allotment, not only to supress weeds and feed the soil, but also to produce a wonderful display of late summer flowers, much loved by bees. The dense foliage also provides the perfect habitat for a range of helpful creatures, such as beetles.

What are green manures?

The term ‘green manures’ applies to a group of annual plants which benefit the soil in various ways, similar to the result of digging in animal manure. Green manures have the advantage of being fast-growing – hence their use as ground cover. Broadly speaking, green manures fall into two categories, for sowing either in late spring through the summer months; or sown in autumn for winter use. As well as other benefits, varieties which belong to the pea and bean family (legumes) have the additional capacity of collecting nitrogen from the air and storing this (‘fixing’) in their root nodules - nitrogen being a valuable plant nutrient. Other varieties of green manures help to break down heavy soil and add humus to prevent erosion.

How to sow green manures

This is the fun bit. Most varieties of green manures have tiny seed which is best broadcast. To make things easy, I tip the entire packet of seed into a shallow plastic pot, ready to take what I need in my hand, then scatter the seed as thinly and evenly as possible over the ground. If sown carefully, a packet of seed goes a long way. I finish off by giving the whole area a gentle raking to settle the seed into the soil and then water well. Sown in summer, green manures germinate quickly and put on surprising growth over the period of a few weeks. Be sure to water young plants during times of drought.

What happens next

Green manures can be harvested before flowering, the growth cut to ground level and dug into the soil to add organic material. If the site is to be used again soon after, leave it for two or three weeks as the decaying green matter can hamper plant growth. If you leave a crop to flower, make sure that you cut and dig in before the plants run to seed or you will have a wonderful new crop when you least want it.

Summer sowing

Phacelia (Phacelia tanacetifolia): best sown from April to August and dug in after two or three months before it runs to seed. Phacelia flowers, a delicate purple with numerous long, soft stamen, are delightful and act as a magnet for bees. If you sow later in the year, the plants may survive over winter if the weather is mild. Crimson clover (Trifolium incarnatum): prefers light soils. Sow from March to August and leave in for two or three months up to flowering. Bees love the crimson flowers.

Autumn sowing

Field, or Winter beans (Vicia faba): ideal for breaking up the heaviest of soils with the added benefit of being a nitrogen fixer. Best sown from September to November, the plants can be left for two or three months until they flower, then cut and dug in.

Winter Mix, a combination of Grazing Rye and Winter Tares: good for sowing in most types of soil and, like Field Beans, will fix nitrogen into the soil.


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