Green waste compost and vermicompost as peat substitutes in growing media for geranium (Pelargonium zonale L.) and calendula (Calendula officinalis L.)

This research evaluated green waste compost (GWC) and green waste vermicompost (GWV) as peat substitutes in growing media used for the production of geranium (Pelargonium zonale L.) and calendula (Calendula officinalis L.). Five growing media were prepared: 100% Peat (P), 50% Peat + 50% GWC (PC), 100% GWC (C), 50% Peat + 50% GWV (PV), and 100% GWV (V). Geranium and calendula seedlings were transplanted into each medium and were grown under commercial nursery conditions for 6 months, i.e., until they attained commercial size. The higher percentage of GWC and GWV in the growing medium could increase bulk density and air space; decrease total pore space and water-filled porosity; and increase pH, electrical conductivity, and macro- and microelement contents. The heavy metal contents of all growing media were within safe ranges. Particle-size distribution and fertility were superior in the vermicompost-based media than in the compost-based media. Geranium growth was reduced in media containing GWC (C and PC). Calendula growth in compost-based growing media was similar to or greater than growth in pure peat. Geranium and calendula growth and flowering were superior in all vermicompost-based media (PV and V) than in the control medium (P). These results indicate that GWV is better than GVC as a partial substitute for peat in the cultivation of geranium and calendula.