Potting Soil – Sterilize

Q: I re-use the potting soil in my containers. Last year, I had some type of crown rot in my impatiens. Can I sterilize it somehow?

A:
It’s important to restore the soil’s drainage capacity as well as its sterility before you re-use it. Mix the old soil 4:1 with perlite to increase drainage. To sterilize it, stir in enough water to make it quite moist but not soupy. Place in a shallow pan in a 180 degree oven for 30 minutes. Be aware that it will smell strongly while it is cooking. Another option is to heat the moist soil in a microwave until it steams for five minutes.