Green manures are particularly effective in a beds where tender plants are removed in the autumn and planting commences again in the spring. Herbaceous borders, summer bedding, vegetable plots or sub tropical borders could benefit from the use of a green manure.
Green manures are also useful when beds that remain unplanted for some time as the presence of the crop not only add nutrients to the soil but also keeps the beds weed free. The plants are sown when the beds are emptied in the autumn and the entire plant (including the roots) is dug in at the end of the winter prior to planting in the spring.
Broad beans are very particularly effective green manure as they have an additional benefit. They have nodules on their roots caused by a bacteria in the soil that helps them to fix nitrogen from the air into the soil, and therefore increase nitrogen levels in the soil. This nitrogen fixing benefits successive plantings considerably as nitrogen is an essential nutrient for leaf growth.
Sow your green manure of broad beans directly into the soil during autumn (October/November) after you have stripped out your summer planting. Prepare the soil by forking over the soil deeply and removing any plant material from the previous planting.
Broad beans like to be planted in slightly firm soil so tread over the bed prior to planting. Sow the seeds 9 inches apart and 2 inches deep and water well. Your beans should germinate within 2-4 weeks. Keep the bed clear of weeds until the beans establish and water if necessary.
A month before you plant out your beds with summer plants chop the border over and leave the plants to wilt before digging over the bed to incorporate the entire plant into the top 10 inches of soil. Allow at least two weeks before planting to allow the beans to break down as decomposing green material will slow down your new plants.
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