Gardening > Condition Your Soil With Green Manures

Condition Your Soil With Green Manures

Green Manures
The term "Green Manure" refers to a variety of crops which are grown simply to be dug into the soil. The purpose of this is to add organic matter to the soil and to provide new nutrients for the plants and crops which will follow the green manure. Some green manures can be grown over winter when it is easier to plan for the plot to be empty. Some however are so fast growing that they can be grown and dug in within a few weeks making these particular green manures ideal for sowing between crops. If this method is used the green manure should not be of the same family as the crop which precedes or follows it (i.e. do not plant brassicas before or after mustard).

Before sowing green manure the site should be prepared as for any crop and it may even be necessary to apply a fertilizer in preparation. The soil should be firmed and then small green manure seeds can be sown in rows about 6 inches apart or broadcast and raked in. Large seeds should be sown in rows about 12 inches apart.

Some green manures can "fix nitrogen" by taking it in from the atmosphere. The nitrogen then becomes available to the soil when the green manure is dug in. Red clover fixes nitrogen and is sown in spring or late summer. It can be left and dug in when the plot is needed again. Lupin also fixes nitrogen and provides phosphates. This should be sown in the spring and cut down in the summer before digging in. A second crop of lupin can be sown immediately and dug in after 2 months. Winter tares and field bean both fix nitrogen and can both be overwintered and then dug in in the spring. Sow field beans in early summer of autumn and winter tares in late summer. Winter tares can also be sown in spring and summer and dug in as required. Alfalfa, also a nitrogen fixer, can be sown in spring for autumn digging or late summer for spring digging.

Phacelia does not fix nitrogen but is very quick growing. It will not survive frost so should be sown in late spring or summer and dug in after about 2 months. Buckwheat, another non-nitrogen fixer, can be sown in spring or summer and dug in during the autumn. Although this green manure does not fix nitrogen it attracts hover flies which will feast on any green fly. Italian rye grass does not fix nitrogen either but it can be sown early in the year in a cold soil and dug in before the first vegetables are planted.

All green manures should be dug in while the stems are still soft so that the plant can break down easily without taking nitrogen from the soil. If the green manure has gone hard and woods it can be soaked in a liquid seaweed manure once it has been chopped up. This will help with the process of decay. It is a good idea to chop the green manure up and to allow it to lie on top of the soil for a few days. It should then be dug in to a depth of about 6 inches.

If you are able to leave a chunk of ground fallow for a while it is well worth sowing a green manure. The addition of any organic matter to your garden is a bonus and green manures are effective at suppressing weeds. Their deep roots can assist drainage by breaking up the soil. Choose the type of green manure you use according to the length of time you are able to leave the piece of ground empty and according to the type of soil in your garden or allotment.

Alfalfa - Suitable for dry conditions but does not like acid soils.
Buckwheat - Produces large amounts of organic matter.
Crimson Clover - Very good for sandy soil.
Red Clover - Can be cut once and left to re-sprout.
Mustard - Very quick growing.
Phacelia - Plenty of dense foliage, dig in before flowering.
Winter Tares - Dislikes acid soil.
Field Beans - Will sprout after first cut to give second lot of foliage.