Use of De-inked Paper Sludge in Potting Mixes for Geranium and Zinnia Production

Abstract

De-inked paper sludge from newsprint recycling was evaluated as an alternative amendment in bedding plant production. `Sweet Dreams' geranium (Pelargonium × hortorum) and `Crystal White' zinnia (Zinnia angustifolia) were grown in square 10-cm pots in one of five media. Media contained 0%, 20%, 40%, 60%, or 80% de-inked paper sludge by volume. All mixes contained 10% perlite, and peatmoss was used to bring the volume to 100%. Initial chemical and physical characteristics of the media were determined. Plants were grown in a greenhouse for 8 weeks, and then plant height, shoot dry weight, and average plant width were determined. Media containing 20% or less paper sludge had an average pH of 4.4, whereas those containing more sludge had an average pH of 7.0. Cation exchange capacity of the media decreased significantly as the volume of sludge increased. Media containing 60% or more paper sludge were better aerated, but held less water than those made with 40% or less de-inked sludge. Geraniums grown in 20% or less paper sludge were at least 18% taller than those grown in medium containing 40% or more de-inked sludge, but average dry weights and plant widths of these plants were unaffected by the media. Zinnia plants grown in 20% or less paper sludge produced four times more shoot dry weight and were at least 34% taller and 20% wider than those grown in 40% or more sludge. Overall, zinnias grown in 40% or more sludge were unacceptable for commercial sale. A volume of 20% de-inked paper sludge could safely be included in potting media used for production of `Sweet Dreams' geranium and `Crystal White' zinnia.