This exhortation from noted Arboretum horticulturist Donald Wyman appeared in the May 5, 1939 issue of the Bulletin of Popular Information (Series 4, Volume 7). His urgent appeal was in response to the significant loss of trees from the Hurricane of 1938 the previous September, but the message is still applicable today. There’s still time this spring to “plan intelligent tree planting programs for the streets and highways as well as on private property.”
While Wyman’s sentiments are still very relevant, tree research over the ensuing 50-plus years has changed some of the recommendations he made in 1939. His adage that “it is always better to plant a fifty-cent tree in a three-dollar hole than a three-dollar tree in a fifty-cent hole” still rings true (although those price points have certainly risen!), but current planting recommendations emphasize the width of the planting area, ideally three or more times the width of the root ball. And, to prevent the development of girdling roots, the depth of the planting hole should never be deeper than the root ball, not even the two inches deeper that Wyman deemed acceptable. Research has also shown that it’s generally not a good idea to add amendments to the existing soil when planting, though loosening the soil in a wide area around the tree is beneficial. And while it was long thought that branches of newly planted trees should be pruned heavily to “balance” lost roots, current thinking recommends little or no branch pruning at planting.
Some of Wyman’s recommended tree species wouldn’t make it on a planting list today. American elm, once the dominant street tree in many communities, was devastated by Dutch elm disease in the decades after Wyman’s article. New disease resistant elm cultivars offer some hope but are not an exact replacement for American elm. The continued spread of emerald ash borer takes both green and white ash off the list. And Norway maple, widely planted to replace American elm, proved to be a tenacious street tree but has also become very invasive in many regions, as has Amur corktree. Fortunately, many of the trees on Wyman’s list as well as a number of new selections make excellent candidates for greening our communities today.
— Nancy Rose, Editor of Arnoldia