Each year at Claines Canna we grow our Cannas in the same beds, heavily fertilized with horse and chicken manure. Reflecting on this we have started to become concerned that our Cannas, a vegetable crop in some countries, is running the risk of disease and low yields, i.e. it faces the same problems as any other monoculture.
As we have nowhere else to grow the collection, we agree that the time has come to think about a winter green manure, rather than covering the beds with weed-inhibiting covers each winter. The intervention of another crop has to be beneficial.
We don’t dig up and transplant the Cannas until late October and most green manures need sowing earlier. However, Field Beans are of the greatest value when overwintered and can be planted up to November. They can be cut once and the tops left to rot down as mulch, and they will re-grow to produce a second flush of foliage before digging in. That appeals to my eco-side.
The green manure can be dug in at any time up to flowering, so that can be done in early May, just before we start considering when to plant the Cannas back outside again.
So what advantage will such a green manure give us? Beans are a crop that is able to make use of atmospheric nitrogen to enrich the protein content of both the plant and seed. They do this by utilising bacteria that inhabit nodules in the roots that "fix" the nitrogen. When the roots decay, the nitrogen in the root becomes available to the following crop as a fertiliser - an important source for both conventional and organic systems. In addition, it suppresses weed growth over the winter and early spring periods.
We will keep you posted over the winter.