THE PROBLEM SOLVER
Stefan says: You tell me your allotment has been worked continuously for 40 years and is now a reservoir of pests and diseases. Your allotment is the most perfect definition of intensive horticulture I’ve seen for some time, and it’s a fact of life that pests and diseases will build up in the soil and in the environment generally whenever their favoured host plant is grown continually or, worse, continuously.
In an allotment, we inevitably grow the same types of plant year after year and many of them are so closely related to each other that pests and diseases can’t tell the difference. There is only one way in which this build-up can be minimised without the use of chemicals and that is by rotation. Divide the allotment into three or four equal parts, grow certain groups of vegetables on each part and change, year by year, the part on which each group is grown. But what good will that do, apart from making life complicated?
There are two main principles behind a rotation. First, while pests and diseases attack closely related vegetable crops, they rarely attack those belonging to unrelated groups and second, relatively few pest and disease organisms can survive in the soil for longer than three or four years. There are
