Using green manures

lupins make good green manureGreen manures can be either broadcast sown (thrown with random abandon) or sown in rows. Prepare the ground thoroughly as you would for any other crop. If you broadcast the seed, lightly rake it into the surface. If sowing in rows, make drills (small trenches) about 30cm (12in) apart with the corner of a hoe and sow in these. Broadcast sowing is quicker and easier, but is wasteful so you will use more seed. For this reason, it's best to sow larger seeded lupins and beans in rows.

Digging in green manures

Just as soon as a green manure has put on some growth it is worth digging in. However, the benefit will be all the greater the more growth you allow it to put on. Most green manures should be dug in before they flower and set seed or before the stems go woody. If allowed to set seed you may find a second generation of green manure becoming a weed problem as they grow up through subsequent crops. If allowed to get woody, the green manure will take a lot longer to break down in the soil and the micro-organisms responsible will remove valuable nitrogen from the soil as they breakdown the woody parts. For this reason, it is worth cutting back long-term alfalfa crops every few months to keep the growth lush and green.

Dig the green manure into the top 15cm (6in) layer of soil. This is where it will decompose most quickly. Cut the green manure a few hours before digging so that the top growth wilts. Use a sharp spade, shears, nylon-line trimmer or even a rotary mower to chop down the green manure, then incorporate everything (including the roots) into the soil as you dig. Leave three weeks after digging on a green manure before planting or sowing the same ground.

How to use green manures

Choosing a green manure