Effects of vermicompost as a potting amendment of two commercially-grown ornamental plant species

We evaluated the feasibility of incorporating vermicompost as a potting amendment into a commercial ornamental production system. Pansies (Viola x wittrockiana subsp. Delta) and primulas (Primula acaulis subsp. Oriental) were grown in peat-based conventional greenhouse medium substituted with 5%, 15% and 25% (v/v) commercial and pig slurry vermicompost. Vegetative growth and flowering were evaluated and compared to plants grown with 0% vermicompost. We observed a general reduction of growth in both species with increasing concentrations of commercial and pig slurry vermicompost. The highest percentage of vermicompost (25%) showed 20% of plant mortality, high levels of stress and damage to the photosynthetic apparatus, as well as a significant reduction in the number and biomass of leaves and in flower production. Most likely, the increase in electrical conductivity and pH interacted synergistically with the decrease in air space produced after the application of vermicompost and were magnified under sub-irrigation, causing the observed effects on plant growth. Therefore the cultivation system must be taken into account when incorporating vermicompost as a growing media constituent in commercial conditions.