Do-It-Yourself Soil Sterilizer

If you do composting in Seattle (or any cool damp climate) and use the compost for potting mixes, seed starting amendments, or mixing into vegetable gardens, you may have noticed a few problems that start "cropping up" (pun intended).

Weeds!  Lots of them!  Cool weather, wet weather, and winter composting are usually different from warm composting.  If you are unable to keep turning over your compost, or don't want to spend the time and effort to do so, your compost never gets going with the microbial activity that heats it up.  This heat kills many seeds, insect eggs, pupae, and diseases in the compost.  If you don't feel the heat or see steam rising from your bin or heap, what you have is worm composting.  That's not a bad thing - worm castings are extremely rich in plant nutrients and have good soil structure - and in some ways more biologically active than warm compost.  For example, nitrogen fixing bacteria survive cold composting. 

Worm Composting - Besides the worms eating your compost, various fungi and insects also get in on the act.  The end result is plenty of rich dark compost - same as with heat composting.  The only problem is that the weed seeds remain viable. Not just weeds either - certain herbs, fruits, and vegetables all have seeds that remain viable after composting.  I've made potting mixes that have everything from grapes to catnip sprouting in great profusion - choking out what I am trying to grow.

Diseases.  There are all kinds of bacterial and viral pathogens that prey on certain species of plants.  Most of them are specific to a certain plant order or genus, such as Solanum (family Solanaceae) which includes tomatoes, peppers, eggplant, and many others.  Both tomatoes, eggplants, and basil are susceptible to a couple of very nasty little fungal diseases known as "wilts".  The most common culprits are either verticillium, fusarium, or both.  These diseases infect the stem of the plant and clog up the vascular system that carries water from the roots to the leaves.  End result - the plant wilts and never really grows.  On hot days the plants droop and languish.  These wilts are carried in the soil, and once they get into your compost, they are there to stay.  You can't get rid of them with sprays or powders, or cultivation practices.  You can shop for seeds that that are resistant to these diseases, but you practically have to be a botanist to understand this.

Insects.  Many types of bugs and insects can survive in your compost - to hatch out in the spring and wreak havoc on your plants.  A prime example are root maggots - these little buggers start as flies (look pretty much like a housefly) who lay eggs around the roots of cruciferous vegetables such as cabbage, broccoli, cauliflower, Chinese cabbage and many more.  These eggs hatch into maggots who feast on the roots of your veggies.  End result - the plant never seems to get going, wilts, falls over, and languishes.  If you pull it out, it will come out without resistance, and you will see little white maggots burrowing through the roots.  Yuck.

THE CURE - Sterilize your compost!  Just sterilize enough to get plants started in containers, and for use in the hole where you transplant your starts into the garden.

 Click Here to see how to make your own home soil sterilizer.