Composting with worms, called vermicomposting, is a wonderful way to turn kitchen scraps and other wastes into nutrient-dense worm castings. You can also use worm compost to make some of the finest compost tea you can feed your plants and soil. Here are some tips for brewing up your very own vermicompost tea.
Gardeners long ago discovered that watering plants with water allowed to have compost soak (steep) in it seemed to benefit plants. That’s because the compost contains microbes, which may help prevent plant diseases and improve soil health, and those microbes are transferred into the water.
Older do-it-yourself methods for making vermicompost tea recommend filling a nylon stocking or burlap bag with worm compost (castings) and letting that soak in a bucket of water for one to two days. Other guidelines recommend placing one to two inches of vermicompost in your rain barrel or watering can and then letting the tea steep. Compost tea brews best at temperatures lower than 80 degrees and warmer than 55 or 60 degrees.
Researchers and organic farmers have discovered aeration can make a big improvement in brewing better vermicompost tea. Adding air to the tea helps keep higher numbers of aerobic bacteria in the brewed tea. You can buy kits with all the materials necessary to aerate your worm compost tea. You can also make your own aerated vermicompost tea without a kit, by aerating the tea as it is brewing using an aquarium pump suited for the volume of your bucket or barrel.
The University of Minnesota recommends aerating the water for two hours, before adding the worm compost to the water, to increase oxygen levels. You can then aerate the brew for two days after adding the compost. A good ratio for making worm compost tea, according to several research-based publications, is one part compost for every ten parts water. You can easily keep the nylon stocking filled with compost submerged by tying it to a length of board (like a 1”x 1” or 1” x 2”) or rod that allows it to hang in the bucket.
There are a couple of things to watch out for when brewing worm compost tea. Chlorinated water will kill the microbes; if you’re using chlorinated (usually municipal) water, let the water sit for a day or so to allow the chlorine to evaporate out, then add the worm compost. After the steeping, the tea should smell earthy, even sweet; rancid smelling tea could indicate microbes present that may not be beneficial for your plants.
Be sure to remove the tea and use it as soon as it’s brewed, before the microbe populations start to decline. Most home gardeners use a watering can to apply their compost teas. A spray bottle or other sprayer can also be used. If you decide to spray your compost tea, be sure to filter it (a coffee filter works just fine) to keep from clogging up the spray nozzle.