Legume is the vegetable garden group containing the peas and beans, they have the unusual ability of adding nutrients to the soil, and as such they are often referred to as a green manure.
Because the beans and peas provide their own nutrition they are not that fussy about the soil, although it should be water retentive. This is how we prepare the soil for the this group.
We use the bean trench method which we start in Autumn the season before planting. It involves diggings a meter wide trench, about half a meter deep, lining it with newspaper, filling to just over half full with kitchen waste, dusting with bone meal or fish, blood and bone fertilizer and covering with the trench soil.
When backfilled the trench will look slightly raised to begin with, but over the winter the weight of the soil will compress the waste, leaving the trench slightly sunken. At this stage it is a good idea to dust some wood ash over the trench.
The newspaper and kitchen waste will retain a lot of water, and also supply some trace elements as nutrition for the plant.
All plants need a balance of nutrients which would usually be provided in the form of Nitrogen, Phosphates and Potassium.
Nitrogen is used in the production of chlorophyll, as well as cell structure, and as this group of vegetable plants has the unique ability to convert nitrogen in the atmosphere to nitrates stored in root nodes, there is no need to add nitrates to the soil.
Although there is no need to add nitrogen to the soil once the plant has stopped producing beans and peas, the leafy part should be cut at the base of the plant leaving the roots in the soil, these nitrate rich root nodes will then rot down releasing its stored nitrogen into the soil. This is why the beans and peas are known as a green manure.
Phosphorus helps in root development, flower formation and seed production, it also helps legumes to produce more nitrogen rich root storage. The bone meal is high in phosphates, but as it is slow to release it needs to be put in the trench before covering.
Potassium provides vigour and overall plant health; it also helps the plant to resist disease and drought. The wood ash is high in potassium and also helps to reduce the acidity of the soil.
Reducing the acid levels in the soil is important in our crop rotation, we follow roots with the legume group, and as the roots tend to be heavily manured, which can make the soil more acid, we need to make the soil less acid as the brassicas follow, and they prefer a more alkaline soil.
In the spring, when the trench as sunk, build a bamboo frame and in May plant the seedlings at the base. Take a look at the growing beans and peas from seed page, tips and advice.