NURTURE
KEYS TO A
H E A LT H Y A N D URBAN TREE SPECIALIST DR. ED GILMAN DELVES INTO THE FACTORS THAT CAUSE TREES TO EITHER FAIL OR FLOURISH
INDUSTRY INSIGHTS WITH
JOHN CONROY
Last issue Florida grower John Conroy talked with Laurie Hall from CHW about Right Plant, Right Place. In this issue, John interviews Dr. Ed Gilman, urban tree specialist, prolific author and environmental horticulture professor emeritus with the University of Florida. For more than 30 years he’s worked with professionals across the industry including arborists, consultants, landscape contractors, growers, urban foresters, planners and landscape architects on understanding the architecture of tree branch and root structure and why this is critical in the success of trees in the landscape. In the July/August issue, John will discuss more about Florida Grades and Standards for Nursery Plants and its impact for the betterment of the industry.
DR. ED GILMAN
John: Ed, let’s start by talking about the main reasons planted trees fail or succeed in the landscape. Ed: There are many reasons for a tree’s success or failure. Primary among these issues is pruning at planting, grades and standards and the root system. John: What issues have you seen when there was no pruning at planting? Ed: I’ve traveled to many countries, have pruned trees and learned a lot from arborists worldwide. The indelible common thread that I have observed is that lower trunk and branch architecture is pretty uniform in regard to urban planted trees. Whether it’s
48 Pro Landscaper USA South May/June 2021
Singapore, Hong Kong, Boston or Seattle, hardwoods of different species have similar structures. In those places and more, after the tree gets installed and established, nobody is really in charge of training the tree to develop sustainable architecture. Landscapers and homeowners might prune the low branches away but don’t always think about the branches higher in the canopy. Without structural pruning, defects can develop which shorten tree life. John: What’s the best way for landscapers to tell if a tree has a proper branch structure? Ed: What we look for is a trunk (central leader), that is considerably larger than any of the branches. It’s best to have branches about half the size of the trunk. Here in Florida, the Florida Fancy or Florida #1 specification requires that no branches are greater than two-thirds the diameter of the trunk. If they are larger than the desirable ratio then you simply reduce that branch to slow its growth by cutting back to a lateral live branch. This process is called subordination. You can develop good branch architecture and still achieve the silhouette customers want: a rounded, upright oval or a pyramid shape, depending on the species. The bottom line is, whether it’s a city, a homeowner’s association, a commercial or residential client, they don’t want trees falling in weather, and they don’t want the replacement cost of a tree that fails due to a weak structure.
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