Worms in the Heat

Erica asked in the comments if I had any advice about composting with worms during hot summers like the ones she has in Houston. As a native Texan myself, I can appreciate the problem. When I was in college, a non-profit I volunteered for held an annual “Anywhere But Austin in August” fundraiser, so named because truly, a humid Texas summer can be unbearable, for both worms and humans.

The worm most commonly used for composting is Eisenia fetida, sometimes called the red wiggler or the redworm. These critters prefer temperatures in the 60-70 degree range, and really can’t take heat much above 85 degrees. So in a place like Houston, you’ve got a couple of options:

First, consider setting up your bin indoors in a garage or basement. The trick is to make absolutely sure that this room stays cooler than the outdoor temperature. Sometimes a stuffy, non-air-conditioned space like this will actually get warmer than a shady area outdoors. Set up a thermometer in your garage/basement and another one in the coolest, shadiest area of your yard and compare.

If you do think your indoor location will be cool enough, go ahead and set it up there, but keep track of the temperature. On really hot days, think of the worms when you pour yourself a cold drink. Dropping a few ice cubes in the bin will cool things off and keep it from drying out. The contents of the bin should be about as damp as a wrung-out sponge, so just add a few cubes at a time to avoid flooding the bin. And never, never run water through your bin—it will upset the carefully balanced ecosystem in the bin and turn the worms, castings, and compost into a nasty, waterlogged mess. During a really nasty heat wave, you might try leaving the lid off (to prevent the worms from escaping, keep a thick layer of damp shredded newspaper on top and leave a light on), or turning on a fan.

If you don’t have a good indoor location, I’d suggest picking the coolest, shadiest, and breeziest area in your yard. If you plan to build your own bin, consider a wooden bin that is sunk into the ground. On hot days, you might leave the lid off but cover the worms with a thick layer of shredded newspaper or rice straw so they won’t be tempted to go exploring. Worm farmers often use a mister to keep outdoor beds cool and damp in hot weather.

Finally, be careful about the amount of food you add, especially in a large outdoor bin. Fresh food scraps do create their own heat in large quantities. Add food a little at a time or “pre-compost” it in another pile and feed it to the worms once it’s cooled down.

OK, tomorrow we’ll get back to the challenges of air travel with earthworms.