Growth of Peppermint in Compost

Abstract

ABSTRACT To evaluate compost as a medium for production of herbs, peppermint (Mentha × piperita L.) was grown in flats of compost in a greenhouse. Composts were made from mixed municipal solid wastes (one high in ammonium; one low in ammonium), biosolids (sewage sludge) mixed with woodchips (one mature, one immature), agricultural wastes, autumn leaves, and yard wastes. The agricultural, leaf, and yard-waste composts were mature. Shoot growth of mint was recorded after an 8-week growth period. Ammonium and nitrate concentrations, electrical conductivity, and pH of composts were determined at the initiation and at intervals during the experiment. Shoot growth was vigorous in all composts except the immature biosolids-woodchips and yard waste composts. Except for the leaf and yard waste composts, these media had sufficient nitrogen for plant growth. High initial ammonium concentrations and high salinity in immature biosolids-woodchips compost were responsible for inhibited shoot growth. Ammonium concentrations in immature biosolids-woodchips compost decreased with time due to nitrification and ammonia volatilization. Limited shoot growth in the yard-waste compost was attributed partly to a low nitrogen content. Results indicated that a compost for mint production should be mature with good availability of nitrogen.