I think
@Emilya would be better at explaining this, hopefully she is around
Until then, this is a pretty good explanation-
Heat treatments raise the temperature of the soil through steam or direct, dry heat to a threshold where the harmful organisms, fungal spores, weed seeds, etc. are unable to survive, and die. Heat treatment is often called sterilization, but this is a misnomer as the soil isn’t completely sterile at the temperatures induced.
It does kill weeds and pests depending upon the internal temperature reached and the length of time the threshold is maintained. Most instructions recommend at least 30 minutes at the given temperature to kill specific organisms (see Table 1) in moist soil or potting mix.
Research has shown that even sterilization significantly reduces the population of beneficial soil bacteria, it does not eradicate them completely. After sterilization, certain species such as
Pseudomonas and
Bacillus, quickly recolonize the soil and their populations reach high levels within a short amount of time. This quick recolonization overrides the initial reduction in populations through sterilization.
Table 1. Target Temperatures for Soil Sterilization of Moist Soil | |
| |
Target Temp | Organisms Killed when Temp Sustained for 30-minutes |
120℉ | water molds (oomycetes) |
145℉ | most plant pathogenic fungi, bacteria, and viruses, worms, slugs, centipedes |
160℉ | plant pathogenic bacteria, soil insects |
180℉ | weed seeds |
212℉ | heat resistant plant viruses and weed seeds |