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12 FALL 2015 ARBOR AGE www.arborage.com INDUSTRY INSIGHTS B&B trees dug properly (i.e., when dormant). PHOTO BY MATTHEW STEPHENS Seasonal Effect: Another Look at "Fall Dig Hazards" BY MICHELLE SUTTON AND MATTHEW STEPHENS The nursery industry is reluctant to dig certain species of trees in the fall, yet the "fall hazards" lists can vary significantly among nurseries. Also varying is the experience of nursery customers, including city foresters who plant hundreds or thousands of trees each year. In addition to digging season, there are other interacting factors at play in the fall planting picture. A MORE NUANCED LOOK "Those fall hazards lists are generalizations," said Cornell Urban Horticulture Institute Director and street tree expert Dr. Nina Bassuk. "Typically the trees that appear on those lists are trees that are more difficult to transplant, period. In spring they don't become easy to transplant; they're just observed to be easier in the spring than in the fall." Tree Pittsburgh Director of Urban Forestry Matthew Erb has overseen the planting of more than 25,000 trees (mostly B&B) since 2008. "I'm sure if you look hard enough, you will find nearly every species on someone's fall hazard list," he said. Oaks frequently appear on fall hazard lists. "We've actually had great success planting oaks B&B in the fall — specifically swamp white oak (Quercus bicolor)," said Erb. "The fall-planted ones even put out typically twice as much growth for us the following spring than do the spring-planted ones." Erb credits Bassuk for this, as her research on methods and times of transplanting swamp white oak spurred him to plant them in the fall. Erb said Tree Pittsburgh has had no problems with B&B fall- planted red maples (Acer rubrum and associated cultivars and hybrids), London planetrees (Platanus x acerifolia), hornbeams (Carpinus spp.) and hophornbeam (Ostrya virginiana), all of which frequently appear on fall hazard lists. Some other "fall hazard" species that Tree Pittsburgh has had success with transplanting B&B in the fall — with caveats