Back to the Future: Planting Large Bare Root Trees

During the annual meeting of the American Society for Horticultural Science (ASHS) in October, 2003, I heard a thought provoking presentation on tree planting by Dr. Nina Bassuk, a researcher with the Cornell University Urban Horticulture Institute. Dr. Bassuk described her 10-year involvement with the urban tree-planting program in Ithaca, NY. Since the inception of the program, thousands of street and park trees have been planted, and much has been learned about practical and cost effective methods for establishing urban trees. By keeping detailed records on the performance of trees in the program, Dr. Bassuk has been able to draw some definite conclusions, a few of which challenge some of the conventional wisdom about how and when to plant trees.

A main objective of Dr. Bassuk’s applied research on the trees of Ithaca has been to compare the performance of 2-inch caliper trees of many species planted either balled and burlapped (B&B) or bare root (BR) in the spring or the fall. Perhaps the most surprising of her conclusions is that, for most of the species she has examined, fall-planted bare root trees performed as well as or better than either fall- or spring-planted B&B trees (dug with a soil ball) of the same sizes and species. Although spring-planted B&B trees have generally shown slightly greater growth than spring-planted BR trees during the first season after planting, fall-planted BR trees have often outgrown spring-planted B&B trees. After the second growing season, there have generally been no significant differences between B&B or BR trees in caliper and shoot growth whether they were planted in spring or fall. In a paper published in the Journal of Arboriculture, Bassuk and a former student documented this to be true for hackberry, hophornbeam and swamp white oak, all of which are considered by many tree professionals to be somewhat difficult to transplant. One notable exception, however, has been scarlet oak, which has consistently had unacceptable mortality when fall planted.

Credit photo to Dr. Dan Struve, the Ohio State University

A 4-inch-caliper, bare root red oak tree in full leaf being carried on one shoulder to the planting hole .

Dr. Bassuk is quick to point out the advantages of planting BR trees. Costs for harvesting, shipping and planting are considerably less than for B&B trees and, since weight is not an issue, a larger root system can be harvested and planted. No heavy equipment is required, and there is less risk of injury to those planting the trees. Also, there is less likelihood of planting too deeply when using bare root trees, since the root flair is in plain view. There are, however, some challenges to overcome before the outstanding success of the Ithaca program with BR stock can be achieved. For example, a critical step is to arrange for the roots to be dipped in hydrogel slurry at the nursery before fall shipment. Dipped trees are placed with their roots in re-usable bags to protect them from desiccation. Although trees must also be tarped during transit, Bassuk has found that they can be stored, un-refrigerated, for several days at their destination with no apparent loss of viability.

Several questions come to mind when considering whether the fall BR tree planting success in Ithaca can be duplicated in Missouri. First, availability of large, locally grown, BR trees is currently a limiting factor. A major supplier to the Ithaca program is Schichtel’s Nursery, south of Buffalo, which grows in a gravelly loam soil, suitable for bare root harvesting. While we have some loess and sandy soils in Missouri that allow easy BR harvest, there is some question whether trees of some species can be harvested early enough in our climate to make them readily available for fall planting. Perhaps a partial answer to the latter problem is to harvest in spring and place trees in a Missouri Gravel Bed in preparation for fall planting. In another presentation at the same ASHS workshop, Dr. Dan Struve reported that 6 of 6 4-inch-caliper red oaks survived when planted bare root, in full leaf in September 2001 in Columbus OH. The trees were dug in March 2001 with a tree spade from a clay loam soil and bare-rooted with picks and high pressure water before being placed with their roots in frequently irrigated pea gravel until field planted in September. The trees produced extensive, fibrous roots, which were easily removed from the gravel and transported intact to the planting site. The most thought-provoking photograph in the presentation was that of a student single-handedly carrying a 4-inch-caliper, 20-foot-tall oak tree in full leaf to the planting hole balanced on one shoulder.

It is interesting to note that, until the mid-twentieth century, it was common to plant large trees bare root. With the advent of mechanical harvesting equipment and container growing technology, bare root planting has fallen out of favor. However, considering the advantages of bare root handling and the high success rates with bare root planting of larger trees reported by Bassuk and Struve, perhaps it is time to bring bare root technology back and put a 21st Century twist on it.

References:
Buckstrup, M. and N.L. Bassuk. 2000. Transplanting success of balled-and-burlapped versus bare-root trees in the urban landscape. Journal of Arboriculture. 26:298-308.

Urban Horticulture Institute: http://www.hort.cornell.edu/department/faculty/bassuk/uhi/index.html

Chris Starbuck, Woody Ornamental Horticulture, UMC (573) 882-9630