220 Growth of Evergreen Shrubs in Potting Mixes Made with De-inked Paper Sludge

Abstract

De-inked paper sludge from a newsprint mill was evaluated as a substitute for sofwood bark in container media. Rooted cuttings of `Youngstown' juniper (Juniperus horizonatlis), Fraser photinia (Photinia × fraseri), and `PJM' rhododendron (Rhododendron) were planted in 3-L plastic pots that contained potting media amended with 0%, 20%, 40%, 60%, 80%, or 90% paper sludge and 80%, 60%, 40%, 20%, or 0%, respectively, bark (by volume). All mixes contained 10% sand and 10% peatmoss except for the 90% mix, which lacked peatmoss. After 19 weeks, plant heights were measured for photinia and rhododendron, but average plant width was measured for juniper. Shoot dry weights were also determined for all species. Juniper and photinia seemed to be the most tolerant of media amended with up to 40% paper sludge, whereas rhododendron was the most intolerant species. Shoot dry weights of juniper or photinia were similar for plants grown in media containing 40% or less paper sludge. Shoot dry weights of rhododendron plants grown in 40% sludge were 23% lower than those grown in 0% or 20% paper sludge, which were similar to each other. Plant heights followed similar trends to those of the shoot dry weights. With the exception of juniper, shoot dry weights and heights were drastically reduced if the potting mixes contained more than 40% paper sludge. These results demonstrated that de-inked paper sludge could be substituted for up to 40% of the bark in a container medium for two of the three species tested.