Abstract

Rhododendron indicum (L.) Sweet ‘Due du Rohan’ and Pittosporum tobira variegata Ait. were produced in 10.2 liter (#3) containers in substrates consisting of 20, 40, 60, and 80% (v/v) composted yard waste mixed with pine bark and coarse sand. Plant growth, substrate physical properties, and N and P leachate were compared with a control substrate of pine bark fines:sledge peat:sand (3:1:1 by vol). Shoot growth of plants in compost substrates was similar or better than control plants and greater with daily irrigation compared to alternate day irrigation. Root growth and percent air porosity declined as compost composition and waterholding capacity increased. Total porosity was generally consistent throughout the study. Irrigation regime had no effect on root growth nor substrate physical properties. Ammonium, NO₃-N, and P concentrations in leachates varied with substrate and time following topdressing with controlled release fertilizer. Both species grew best in the 40% compost, 50% pine bark, and 10% sand substrate.