Compost and vermicompost of horticultural waste as substrates for cutting rooting and growth of rosemary

• Compost mixes were more alkaline than vermicompost ones.
• Compost-rich substrates had excessive salinity.
• Ninety percent rooting of rosemary cuttings in vermicompost-based growth media.
• Dilution with peat improves compost based substrates for rooting.
• Improved pH, EC, Vair and Vwater after six-month plant growth.

Peat replacement is an issue that receives much attention in the horticulturist agenda. Several organic materials have been suggested either as substrates or as substrate constituents. This study aims to determine how three such materials, one compost and two vermicomposts, affect the rooting of cuttings and plant growth of rosemary plants grown in pots. The compost (C) and vermicomposts (V1 and V2) were obtained from the same batch of tomato crop waste. Each material was mixed with peat at several proportions. Two experiments were carried out in nursery conditions. In the first, rosemary cuttings were grown in each mix and rooting was quantified. In the second experiment, rooted seedlings were grown in each mix to marketable size (six months after the seedling transplant). The physical, physico-chemical and chemical characteristics of the initial mixes and of the mixes at the end of the six-month experiment were determined. The physical properties of the substrates were within adequate ranges. pH was fairly alkaline, especially in C and salinity was particularly high in the C-based mixes. Soluble mineral contents in C were much higher than in V1, V2 or peat. Mixing with peat produced substrates with intermediate characteristics. Both vermicomposts outperformed compost and peat for rooting cuttings. The presence of hormone-like substances in the vermicomposts might be behind this effect. The vermicompost-based substrates gave acceptable results for growing plants, though none performed as well as the control. Nitrogen and potassium contents in cuttings and ready-for-sale plants were low and phosphorus content was very low compared to sufficiency ranges, which led to a recommendation to increase fertilization. At the end of the six-month experiment, the mix properties had changed, representing an improvement in the substrate quality that might be taken into consideration when transplanting the rosemary to the soil.