Green manures or cover crops are an inexpensive way to improve both the structure and nutrient content of your soil. Cultivated primarily to add organic matter to the earth, a green manure crop is usually grown for a short period of time, then chopped down and incorporated into the soil. They are a great option when preparing new land for use, forming a green carpet that stops weeds colonising and prevents nutrients from being washed away.
Traditionally, green manures have been used on arable land or allotments, but they are equally useful in gardens. All you need is a packet of seeds, a spade, and patience while they do the hard work for you.
Field Beans, like all of the bean family, is a nitrogen-fixing plant. It has nodules on its roots where nitrogen-fixing bacteria live in a fascinating mutual relationship- the bacteria transform nutrients from the air into a form usable for the plant, and the plant feeds the bacteria with sugars from its roots.
The popularity of Field Beans for use as a green manure has increased steadily over recent years due to its value to organic farmers as a full-foliage legume with deep nitrogen-fixing roots. Often referred to as 'Winter Field Beans' they are very hardy and suitable for overwintering. It prefers moist soils and will not tolerate drought conditions. It is particularly good on heavy soils, the deep strong roots penetrate the soil helping to break it up and improve its structure.
Sown in September to late November for turning in spring prior to flowering, allow to grow to about 45cm tall, then either cut down and dig in during spring, or cut down then allow to re-grow and then dig in.
Field Beans are easier to turn under using hand tools compared to other cover crops.
Sowing Period: September to late November
Soil: Most soil types, including heavy soil. An excellent nitrogen fixer
Growing Period: 3 to 6 months.
Coverage: 250g covers 10 square metres.
Field Beans are usually sown in September to late November. Very hardy, they are left to overwinter and dug into the soil in spring.
They can also be sown in spring as soon as the soil conditions allow in February or March. A cool-season annual, field beans can tolerate frost but are killed by temperatures below -12 to -9°C (10 to 15°F).
Prepare the soil by removing weeds, digging over if it hasn't been recently cultivated and raking level. The large seeds can either be hand sown or can be scattered thinly over the surface of the soil.
Sow the seeds 5cm (2in) deep. Ensure that the plants are spaced a minimum of 23cm (9in) apart each way. Water in well. Bare patches should be covered within two to three weeks and plants will do the most good if they are left for around eight weeks before digging in.
When it is not being grown for seed it should be mowed down shortly after it starts to flower, in order to avoid problems with volunteer seedlings in the next crop. If plants start to flower before this, cut off the tops and dig in otherwise the nitrogen is lost. Leave the green manure to decompose in the soil for up to four weeks before growing vegetables.
Field Beans begin flowering in June and mature in mid to late September. For maximum nitrogen gain, chop plants down and turn them under as soon as they begin to bloom. Leave three to four weeks before for the new seasons planting.
Field Beans are easier to turn under using hand tools compared to other cover crops but if digging in is difficult for you, the plants can also be pulled up and composted.
Rotate green manures as you would any other crop. Field beans as a member of the legume family can be sown in rotation after summer legumes to overwinter in a crop rotation plan. Follow with Brassicas and they will benefit from as nitrogen helps to promote the green leafy growth that we eat, for example cabbages, kale etc.
Field Beans can be under-sown with low-growing forage legumes, such as clover. This can be an effective way to control late weeds.
They can also be sown together with Cereal Rye, Oats or Wheat.
- Additional Information
Common Name Winter Field Bean Other Common Names Winter Field Bean Family Leguminosae Genus Field Beans Hardiness Hardy Annual Flowers White Flowers Natural Flower Time in summer Height to 100cm (to 36in) Time to Sow Sow in September to November for digging in or overwintering Time to Harvest 3 to 6 months Coverage 35kg per acre - 100gm covers 12 square metres