By Jim McCausland, Sunset senior garden writer

“You get hundreds of times more microbes coming out the back end of a worm than go in the front,” says Dr. Clive Edwards, who does research in the Soil Ecology Laboratory at Ohio State University. And that may explain why vermicompost tea is superior to conventional compost tea at boosting plant growth and controlling diseases, insects, and nematodes.

Vermicompost tea is made by putting 1 part worm castings into 4 parts water, and brewing it for 24 hours in a unit like one made by Growing Solutions. You can buy worm castings at many nurseries, or produce them in a worm bin (download plans from Oregon Soil Corporation). Use the resulting tea as a soil drench or as a foliar spray. The sooner you use it the better; maximum shelf life is probably around a month.

Dr. Edwards says the tea is helpful in three ways. The most important may be in its beneficial growth regulators, which promote increased seed germination, growth, and leaf size. The tea also helps control diseases such as Pythium, Rhizoctonia, and Verticillium. But arthropod control (arthropods include insects, custracians, and spiders) is what surprised Edwards most. “I thought we might get disease control,” he told me, “but I was surprised when this was also effective against insects.” Applications every week or two can control white cabbage butterfly caterpillars, spider mites, aphids, mealy bugs, cucumber beetles, and tomato hornworms.