Transplanting hackberry
In the late 1990s, Cornell Urban Horticulture Institute (UHI) conducted a study
comparing balled-and-burlapped (B&B) and hydrogel-dipped bare root (BR) trees
harvested at 1.5-inch/40 mm caliper and planted in pairs in the urban environ-
ment of Ithaca, New York. Half of the B&B-BR pairs were planted in spring, half
in fall. One of the species studied was hackberry (Celtis occidentalis).
With growth measurements repeated in years 1, 2, and 3, and with anecdotal observa-
tion in years since, we found that hackberry can be successfully transplanted in fall or
spring, B&B or BR. However, we found that fall-planted BR hackberry had a slight edge
over spring-planted BR hackberry, and that when it came to spring planting, B&B hack-
berry trees grew somewhat better than BR hackberry trees. We concluded that if a
community wants to try planting BR hackberry trees in order to save resources, preserve
fine root systems, and allow more public participation, they should do it in the fall.
It is important to note several caveats. BR trees were hydrogel dipped per the
process described in the UHI booklet, Creating the Urban Forest: The Bare Root
Method. The dipping procedure is a critical element in the handling of BR trees.
Because we do not assume that larger-caliper BR trees would perform the same
way as small-caliper trees, only trees under 50 mm (2 inches) caliper should be
used to ensure survival and transplanting success. Trees of any caliper must receive
adequate early maintenance in terms of weeding, mulching, and watering.
— Dr. Nina Bassuk, Urban Horticulture Institute
Director, and Michelle Sutton, City Trees Editor
"My experience with hackberry over the years is that it is not as drought
tolerant as reported. In a droughty situation, the leaves can become some-
what yellow (not in the same way as the yellow presented by interveinal
chlorosis). It also suffers from nipple gall and witches' broom. Overall it is a sur-
vivor, but folks should be aware of some of hackberry's limitations."
— Nina Bassuk, UHI Director
The SMA 2020 Urban Tree
of the Year designation rec-
ognizes hackberry (Celtis
occidentalis) for its service to
urban forests and encourag-
es its use when matched ap-
propriately to site and as part
of a diverse urban tree inven-
tory. You can see the full list
of past Urban Tree of the Year
winners on the SMA website.
Alternate foliage of hackberry, shown here in
fall season. Photo by Michelle Sutton
Photo by Tara Costanzo
www.urban-forestry.com 39
