Using the heat of the sun to sterilise seed beds is a cheap and simple method of sterilising soil. When planting seed beds it is very helpful first to reduce the number of micro-organisms found naturally in the soil which can cause disease. There are chemical methods of doing this but they are expensive and may result in pollution.
Solarisation is a technique developed in Israel in 1974. It uses plastic sheets to cover the soil to be prepared as a seed bed.
- First prepare carefully the area to be used as a seed or nursery bed. Remove stones and rubbish, dig and level the soil.
- Water it very well.
- Cover it using a clear plastic sheet. The bed must be narrower than the plastic sheet. If the plastic sheet is 120cm wide, for example, prepare a bed that is 90cm wide. Bury the edges of the plastic in a small trench and cover them with earth to hold the plastic in place.
- Leave the plastic covering the soil for five sunny days. If there are cloudy days, leave it covering the soil for longer. The heat of the sun through the plastic will warm the soil to very high temperatures (40–50°), killing most micro-organisms and weed seeds. After removing the plastic carefully so it can be reused, plant the seeds immediately to gain the maximum benefit. You will notice that there is a higher rate of germination (so you will need fewer seeds) and better growth.
Information on desinfestacion de semilleros sent in by Leyder Ruíz and Jorge Giraldo of IMCA, Buga, Colombia.