Thirteen species of temperate landscape trees and shrubs grown outdoors in Mobile, Alabama from March 26, 1985, until June 5, 1986, were exposed to natural (NP), night interrupted (NI), or extended (EP) photopenods from June 21 until November 15. Shoot growth measured in December varied among species but was either greater under long day conditions or similar to growth under NP, whereas root development was greater with NP or unaffected by photoperiod. By June 1986 shoot growth was either greater under NP or similar to growth under EP or NI. Root growth patterns were similar to those observed in December. Six species exposed to long day conditions exhibited extensive twig dieback, following subfreezing winter temperatures.
2Assistant Professor of Horticulture and former superintendent, Ornamental Horticulture Substation, Mobile, Ala., resp. Current address of junior author: Cottage Hill Nursery, 9960 Padgett Switch Rd., Irvington, AL 36544. AAES Journal No. 11-871240.