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Historic New England recently used a process called air spading to help preserve two large hemlocks at Roseland Cottage in Woodstock, Connecticut. Planted by Henry Bowen c. 1846, the trees, which frame an entrance to the property’s barn, are an important component of the landscape’s design theme.
As part of a professional assessment in 2009, an arborist noted that “these are wonderful old specimens that appear to be in good health; there was no evidence of adelgid infestation but they should be monitored annually for this pest.” Since that assessment, the arborist has noticed a decline in the health of the hemlocks, exacerbated in part by a series of relatively dry summers. The arborist also observed significant soil compaction, a debilitating condition that interferes with optimal growth. Soil compaction and drought increase the trees’ vulnerability to insects and disease.
In 2010 Historic New England removed dead branches and treated the hemlocks for pests such as scale, mites, and adelgid, all indications of a tree in decline. In 2012 measures were taken to address soil compaction by using an air spade to loosen the soil around the root zone. An air spade blows high-pressure compressed air that churns the soil. Looser soil increases pore space, allowing organic matter to work its way in, which improves water retention and helps with fine root growth.
Using high-pressure air estimated at forty to fifty psi, the air spade loosened the root zone around the hemlocks to a depth of three to four feet. The use of air in this environment is far less traumatic and damaging than the use of tools such as shovels, picks, forks, or rototillers. After the decompaction was complete, approximately one yard of fresh compost was tossed into the area and gently raked into the air to mix with the loosened soil. During this process, the workers did not step into the area in order to avoid compacting it.
We continue to assess ways to help avoid undue trauma and compaction to these important hemlocks, such as re-orienting Roseland Cottage tours or changing vehicle access routes. To learn more about Historic New England’s approach to caring for trees, read our white papers on tree care. To support essential preservation projects at our historic properties please consider donating to the Preservation Maintenance Fund.