When I think of poop, I don’t think of the waste that comes out as being better than what was ingested. This is actually the case, though, with our friends the earthworms. Earthworms decompose organic waste, turning it into castings that are more beneficial to plants than many other composts. Earthworm compost is sometimes called vermicompost. Most composts go through a phase of high heat, which kills many of the microorganisms that are beneficial to plants. Earthworms break down waste at cooler temperatures, preserving many of the beneficial microbes. Earthworms not only preserve microorganisms, they also carry microbes with them that help in the decomposition process. Between the earthworms and their microbial friends, the waste they feed on is broken down into castings that are highly nutritious for plants. These nutrients are more easily taken up by plants than those in other composts. The resulting compost also has greater moisture holding properties. The benefit of this nutrition doesn’t stop with the plant; it results in fruit and vegetables that have a higher nutritional value and a sweeter taste.
The microbes in earthworm castings produce plant growth hormones such as indole acetic acid (IAA), kinetin and gibberellins, as well as humates and fulvates. For the plants, this results in higher germination rates, earlier flowering and higher yields. Studies have shown the microbes in vermicompost help protect plants from pests. The observations of Norman Q. Arancon and Clive A. Edwards at Ohio State University have shown the suppression of chewing caterpillars and beetles, as well as sucking insects like scale, mealy bugs, aphids and spider mites. The earthworm castings not only make plants less attractive to pests, but also decrease insect reproductive rates if present. Protections don’t stop at insect pests. The microorganisms in vermicompost protect plants from many diseases, as well. The studies of Norman Arancon and Clive Edwards have shown the suppression of Pythium, Rhizoctonia, Plectosporium and Verticillium. They also noted the suppression of parasitic nematodes and reduced nematode crop damage.
As with any other compost, there can be too much of a good thing. While planting directly into earthworm castings doesn’t kill the plant, they seem to do better in a mix of about 20-40% added to whatever planting medium is used. We usually recommend about a handful per plant, mixed in to, or sprinkled on top of, your soil. A couple of applications per season usually does the trick!
Vermicompost “tea” can also be beneficial. A simple “tea” mixture can be made by adding two cups of earthworm castings to 5 gallons of water, directly or in a mesh bag. Let the castings in the water sit overnight and then water plants with the “tea” the following day. Even more benefits are observed when aeration and “food” are added to the brewing process.
In order to protect Elkhart’s drinking water (Wellfield is the source of about 70% of Elkhart’s drinking water), we employ safe and organic practices to improve the soil and health of the plants in the gardens. At Wellfield, we incorporate earthworm castings into our potting soil mix when planting the potted plants displayed around the Gardens. We source our earthworm castings from a local company called R.A.W. Sustainable Living, and you can too! Look for castings to arrive in our Visitors Cottage gift shop sometime around April 1; they are available in 5 pound or 25 pound bags.
Amy Myers, Horticulture and Facilities Manager