Sow green manure as soon as you empty a space, even 4 weeks can be enough to get a good amount of green growth using spinach or mustard.

Green manure is a crop specifically grown to create organic matter to be composted or dug into the soil. When dug in the green manure provides humus and nutrients to the soil.
Each green manure variety adds to the quality of your soil, Lupins deep roots help break up clay and many bring beneficial insects into the garden.
The mere fact of using green manures stops goodness being leached out of the soil when it has no other crop.

Green Manures to Sow for Summer

• Buckwheat deep rooted for poor soil conditioning.
• White Clover a nitrogen fixer
• Yellow trefoil for moisture retention
• Mustard but avoid if you suffer from club root as it is a brassica.
• Phacelia see photo below
• Agricultural Lupins deep rooted nitrogen fixer
• Spinach or calendula grow and rot quickly.

Over Wintering Green Manure to Sow

• Red or Crimson Clover see photo above.
• Alfalfa deep rooted nitrogen fixer good for trace elements.
• Field Beans fast growing nitrogen fixer
• Fenugrek
• Ryegrass humus from green matter
• Comfrey

How To Sow Green Manure

Broadcast seeds directly onto the soil in autumn, early or late spring. Some quick growing crops can be sown as late as June or even early July When the plants have reached a certain height they can be simply dug into the soil.

Advantages of Green Manures

• They provide soil cover making weeding less intensive.
• Help add organic matter to soil; this improvement will help boost fertlity and the water retention qualities of the soil.
• Makes excellent use of a plot of land that is not going to be used for a year.
• A crop of buckwheat can be ready to dig into the soil in just 6 weeks.

Why Sow Green Manure

• On a new allotment sow green manure on all but one area where you can then focus your energy. The green manure will be improving your allotment whilst you concentrate on one section.
• Green manures stops goodness being leached out of the soil by heavy rain when the land is fallow.
• Green manures suppress other weeds and attract insects.
• Use green manure to help moisture retention and soil erosion.
• Green manure helps soil conditioning by aeration, added trace elements and compostable leaves.

If you managed to sow and over-winter a green manure crop, then February or March is the right time to begin digging it in while it is fresh and green. Green manure is environmentally friendly and can improve the health and condition of your soil without chemicals.

Winter Green Manures

• Crimson Clover for good ground cover that will help with weed suppression a nitrogen fixer. Suits most soils especially useful in sandy ones as it likes it free draining.
• Mustard is quick growing and can be sown from March – September. It suits most soils producing lots of leafy growth good for soils lacking organic matter, helping to improve soil texture and give better moisture retention.
• Red Clover is a fast growing perennial that can be left in situ for some time. It’s deep penetrating roots are excellent nitrogen fixers and penetrate the soil helping to improve its structure. It can grow in most soil types.
• Rye can be used anywhere in crop rotation plans and is one of the best for over wintering. Rye has deep penetrative roots that help fix nitrogen and break up heavy soils and so improve soil structure. It is brilliant at suppressing weeds as it grows quickly and continues to grow in cold conditions.
• Phacelia germinates at low temperatures and is ideal for sowing from March until September. It will grow up to 1m in height and is tolerant of cold temperatures and may over-winter if its not too cold. Phacelia self-seed very easily so dig in before flowering or cut down and compost the foliage.
• Forage Pea like all members of the legume family is excellent for fixing nitrogen . For over wintering this pea should be sown from September to November

Seed merchants like Thompson & Morgan supply high nitrogen mixed seeds and Sow green manure.com specialise in specific varieties.

Cultivation of Green Manures

• Green manure will break down easier and quicker if you do not leave it to get too tough.
• Chop it up well with your spade or go over it with a strimmer before digging in as this will help break it down, the finer the chop the quicker it breaks down and the better it will be for your soil.
• Green manures suppress weeds and help prevent nutrients being washed out of the soil by rain and snow.
• They add humus and release nutrients slowly into the soil making them readily available to following crops.
• Avoid planting for 2 – 3 weeks to allow the process of breaking down from soft green plant material to wonderful humus to start.
• Vetches and legumes fix nitrogen in the soil.

Credits
Clover field 8177 by christian lanctot CC BY-NC 2.0
Phacelia (Phacelia tanacetifolia) by anemoneprojectors (back soon??!) CC BY-SA 2.0