Green manure are crops of selected annual and perennials that can be grown to cover beds – often over winter – and then dug in to add organic nutrients and matter to poor soil.
- Green manures help from ground becoming overly compacted and also help to maintain the space and keep weeds down.
- The organic matter green manure supplies to the soil feeds root-zone micro-organisms.
- Green manures prevent nutrients being leached from the soil by taking up nitrogen into their foliage and then releasing it back when they are dug into the ground; this sometimes negates the need to add nitrogen fertiliser to the next crop grown in that plot.
Legumes such as clover, trefoil and vetches fix nitrogen via bacteria in their root nodules in the summer (but don’t fix so much nitrogen in winter).
Hardy green manures for overwintering allotment beds
- For August sowing, scatter seeds of clover, trefoil and common vetch.
- Cut top growth and dig in before it flowers. Then leave 6 weeks before sowing a new crop.
For spring sowing
- In spring use mustard seed for green manure. Rake broadcast sown seed into soil and firm by treading. Once grown, dig these in or plant crops direct in spring.