When growing in greenhouse borders, reduce the build-up of soil borne diseases by digging out the soil every three to five years and replacing it with bought-in top soil or good garden loam. Grafted plants may help where soil problems are suspected (aubergines and tomatoes are now available).
Large pots and growbags are an alternative where soil is suspect. Cover soil with plastic sheeting, ideally white, and place pots or bags on this. Potting media including growbags can be re-used at least once for different crops if no diseases are present.
Glasshouse red spider mite