Soil Sterilizer

Saturday, 1st October 2005

Camplex sterilizer
There's room for a cubic foot of soil in the top of the sterilizer

I've had a question from India, from a Mr Sondhi, asking where he could buy a soil sterilizer, like the one that I've mentioned in this diary.

This Camplex Soil Sterilizer, was my dad's. Although it dates from the 1960s it still works well.

sterilizer base
There's a kettle element
in its base

Cooking up Compost

I find that steaming the soil for 15 or 20 minutes kills all the weed seeds. I wouldn't bother doing this when I'm mixing ordinary potting compost - I just pull the weeds out as they appear - but it's essential when mixing seed and cutting compost. The steam also kills some bacteria.

A foot square (30 cm) perforated metal sheet (right) supports the soil and allows the steam to rise through it. There's a hole in the lid to allow the steam to escape.

I love that promotional plastic ruler! (c. 1970?)


Homemade Solar Soil Sterilizer

based on a design by John Detka (see link below)
second inner box
1. Put a layer of crumpled newspaper two to three inches (5 to 8 cm) deep in the bottom of a large cardboard box.
2. Place a smaller cardboard box inside and fill the 2 to 3 inch cavity between the two boxes with more crumpled newspaper, tightly packed.
3. Cover the gap around the top with folded card and line the inner box with aluminium foil, using a non-toxic glue.

cardboard box solar soil sterilizer4. Paint the top rim of the box with matt black paint or cover with strong black paper. You could try painting or covering the sides too, to boost the absorption of heat from the sun.

5. Use a sheet of clear plastic as a lid.

6. Put your soil inside then use duct tape around the edges to hold the lid in place with an air-tight seal.

7. To destroy weed seeds, the soil should reach a temperature of at least 180°F . The oven should be capable of reaching 275°F.

Note: I've never tried making one of these; once you've worked out the principle of the solar oven you'll be able to make your own improvements. If you do try it, please let me know how you get on. Next Page


Making a Cardboard Box Solar Soil Sterilizer by John Detka (after a design by Barbara Kerr, 1976)

Soil Sterilizers at Pro-Grow, Wisconsin

Richard Bell,