RESEARCH REPORT: Worm Casting Application Methods and Impact on Yield
Worm castings, or vermicompost, are a common addition to potting soil mix and greenhouse bedding, and are recommended for use with nearly any plant as an addition at seeding or transplant, used to side-dress during the growing season, incorporated to compost piles or vegetable beds, or steeped as a compost tea and added during watering or as a foliar spray. According to the product information, worm castings help improve soil structure, provide beneficial microbes, increase water retention capacity, and provide slow-release nutrients.
The effects of worm castings on vegetable yield are examined in the scientific literature pertaining to peppers, tomatoes, strawberries, and marigolds and seedlings in greenhouse and field trials. Results are mixed, but several studies show yield increases by using up to 40-50% worm castings in the potting mix in greenhouse settings.
Two vegetable farms, Middle Way Farm (Jordan Scheibel) and Scattergood Farm (Mark Quee), designed a field trial to determine if different types of worm casting application would cause significant yield differences in cabbage. Three different methods of application were used: incorporation during seeding, application at transplant, or application as a bi-weekly foliar spray.
For this trial, no significant differences were seen among treatments, however, Scheibel and Quee both intend to try the experiment again, refocusing on application methods that held the most promise for them. Both farmers found the foliar application to be tedious, and plan to focus on multiple side-dressings vs. no treatment for the next round of research.