Sterilising soil

Press, Volume CXII, Issue 32879, 30 March 1972, Page 13

Sterilising soil

In the preparation of potting compost or seed-rooting mediums containing soil, only sterilised material is used by the nurseries. This is most desirable as it eliminates such insect pests as wire worms and nematodes, and also soil-bome fungus diseases, many of which can remain viable in the form of spores for many years. Sterilisation will also destroy weed seeds which are ever present in the open ground. Sterilisation of soil is carried out either by chemical Application or by steam. Steam sterilisation, probably the easiest and safest method for home garden preparation, has the added advantage of releasing or making more available soilheld plant nutrients. The simplest method of steam sterilising a small quantity of soil is by using a large pot or similar container which can be sealed with a tight fitting lid. To this should be added about J inch depth of water. When this has been brought to the boil, soil should be added. The soil should be as dry as possible and sieved before putting into the boiling water. The contents of the receptacle should be allowed to simmer for 15-20 minutes after which the soil should be tipped out on to a perfectly clean surface to cool and drain.

Alternative methods employ the use of chloropicrin, D.D., ethylene, dibromide, formaldehyde or methyl bromide, all of which have certain advantages and disadvantages but have one thing in common: they are dangerous arid must be handled carefully. In the process of sterilising the soil all seed trays and other containers should also be given similar treatment—dirty or old boxes and pots can harbour pests and diseases just as well. It would rather defeat the whole objective of the exercise to attend to one and not the other.