Investigating Vermicompost as the Primary Fertilizer Source in Organic Vegetable and Flower Transplant Production

Fertility management in production of organic transplants can be difficult. Transplants are grown in containers with a small substrate volume and most substrates have a low nutrient holding capacity. Organic fertilizers often have low levels of plant available nutrients that are not supplied in the correct proportion to plant needs. Composts are commonly used in organic substrates but they may be low in plant available nutrients and microbe mediated nutrient release happens slowly. Commercially produced dairy manure vermicompost (Worm Power, Avon, NY) is a worm processed form of compost that can be used in organic production. Our first objective was to determine the seed germination and plant growth response of pepper (‘Calwonder’), tomato (‘Rutgers 39’), petunia (‘Celebrity White F1’) and snapdragon (‘Rocket Mix F1’) to vermicompost (VC).  Germination trials were conducted using 0%, 4%, 8%, or 12% VC by volume incorporated into the peat-perlite substrate prior to seeding or topdressed at the same rates after 2 weeks. Incorporating the VC into the substrate did not significantly affect germination percentage of any of the species tested. Dry weight (DW) was increased for 8% and 12% compared to 0% VC for tomato, petunia, and snapdragon. Pepper DW was significantly larger for 8% than 0% or 4% VC. Topdressing VC as opposed to substrate incorporation allowed all species to better utilize the vermicompost and produce larger plants. When VC was topdressed, a significant enhancement in growth compared to control (0% VC) was apparent at 4% VC; whereas 8% VC was required for a significant growth benefit when incorporated. Our second objective was to determine the effect of VC on the same species when transplanted into 4-inch (500 mL) containers. VC was incorporated into a peat-perlite substrate at rates of 0%, 5%, 10%, 15%, 20%, or 30% by volume. Four-week-old seedlings were transplanted into the substrate and harvested after 5 weeks. The addition of VC at 10%–30% increased the DW of tomato and pepper plants as compared to the control substrate. For petunia and snapdragon transplanted into 4-inch containers, 10% appears to be optimal, additional VC led to a decrease in DW. Weekly leachate samples exhibited an increase in pH and a decrease in EC over time. Nitrate concentration in leachate decreased over time and was completely depleted by week 3. Ammonium also decreased over time but was still present in low quantities at weeks 3 and 4 for 10%–30% VC treatments.