An allotment or garden is a highly intensive way of working the soil, but we don't have space to allow some land to lie fallow with a cow grazing.   Green Manures do the job of a fallow patch; they are not a substitute for adding compost or manure, but a complement to it.   Dig them in before they flower, or become woody - best when they are still young and soft.

They can help in several ways

• retain and recycle nutrients from the soil; or draw up valuable micro-nutrients from the sub-soil
• some (the legumes) go further, and "fix" nitrogen in the soil, ready fertiliser for the next crop;
• form humus as they rot down;
• cover bare soil and stop nutrients washing away in heavy winter rains;
• smother weeds, as most grow fast with masses of foliage;
• some of them do a good job of digging;
• some attract bees and other beneficial insects, or provide cover for friendly predators.

Any time you have a patch of ground which looks as if it will be bare for six to eight weeks or so, sow some appropriate green manures.   This is especially valuable through the winter.

I've found it hard to get good information on the subject, so for what it's worth, I've summarised some experiences - from my plot, and from other people.   Please do add to it if you can!

• Some useful green manures
• Fitting into a rotation (important!)
• What to use when!

The HDRA has produced a good How to - Green Manure introduction.