Influence of Compost Aging and Fertilizer Regimes on the Growth of Bedding Plants, Transplants and Poinsettia

Rooted cuttings of poinsettia (Euphorbia pulcherrima Willd. ex Clotzsch ‘Amy’) and seedlings of bibb lettuce (Lactusa sativa L.), baldhead cabbage (Brassica oleracea L. var. Capitata), sweet william (Dianthus barbatus L.) and pansy (Viola & Wittrockiana Gams.) were grown in Sunshine Mix and 7 experimental media containing 30-day-old (“New”) or 90-day-old (“Aged”) cocompost (polymer dewatered sewage sludge composted with processed garbage), perlite or vermiculite, and peatmoss. Plants were fertilized biweekly with water soluble fertilizer of 25N-2.2P-16.6K (25-5-20) at 250 ppm of N applied at 0, 1 or 2 wks after transplanting. The growth of all species did not vary with compost age. Dianthus and pansy plants grown in 50% “New” compost and dianthus grown in 25% “New” compost produced significantly lower top dry mass than those grown in Sunshine Mix. All other treatments for cabbage, lettuce, dianthus and pansy showed no significant difference in top growth from those grown in Sunshine Mix. Poinsettia plants grown in Sunshine Mix produced greater total growth than all other treatments except those grown in equal portions of “New” compost, peat and perlite. Lettuce and cabbage leaf tissue contained cadmium levels less than 0.5 ppm regardless of compost level.