Growth of 'Cunningham's White' rhododendron in plastic and fiber pots treated with copper hydroxide

Abstract

Shoot and root growth responses of 'Cunningham's White' rhododendron (Rhododendron x) was studied when grown in black plastic or molded fiber pots treated with copper hydroxide, or not treated, Containers of two sizes were studied, and the influence of pot type on substrate temperature was recorded. Rhododendron shoot height and dry weight was not influenced by pot volume, pot type, or copper treatment at 49, 131, or 362 d after potting. Rhododendron shoots were larger when grown in 3.8-L (trade 2-gal) pots compared to 2.8-L (trade 1-gal) pots, or when grown in 3.8-L fiber pots compared to 3.8-L plastic pots, both 131 and 362 d after potting. Copper treatment did not influence shoot size. Copper treatment reduced the amount of circling or matted roots at the container-substrate interface for both plastic and fiber pots, but there was better control of root growth in 3.8-L pots compared to 2.8-L pots. Substrate average minimum temperatures were warmer, and average maximum temperatures were cooler when pots were located near the center of the growing block compared to the southwest corner of the growing block. Substrate average maximum temperatures were cooler in fiber pots compared to plastic pots, but only when pots were located on the southwest corner of the growing block.