Roots – A Girdling Mystery

From a recent article in Nursery Management July 2012 pages 24-25

5 years ago, a team of Minnesota researchers, including Jeff Gillman, associate professor at the University of Minnesota planted 4 different species of trees, Acer platanoides ‘Deborah’ - Norway Maple, Acer ‘Sienna Glenn’ hybrid Silver-Red Maple, Thuja ‘Techny’ - Arborvitae and Malus ‘Red Splendor’-Crabapple.

Before planting, on one group they severed the roots on the root ball on all sides and across the bottom. On another group, they cut the root ball into a cube/box. And on the controlled group, of course, they did nothing. All were planted with standard planting depth recommendations, so the top of the root flare was at proper grade, or so they thought they had planted at the proper grade.

After 5 years of growing, they dug up the balls to determine which ones had the most girdling roots. On a somewhat surprising fine, doing nothing to the root ball at the time of planting had about the same effect on the types of roots. Girdling roots are those that grow  around or above the base flare of the tree. This is akin to wrapping your hand around your wrist, and squeezing so hard as to cut off the blood supply to your hand. Girdling roots can reduce or cut off the flow of water from the roots up to the leaves.

But what was surprising to the team was that even if a small amount of the trunk flare was planted below grade, girdling roots were found on all of the ‘accidentally planted too deeply’ trees.

So from this study, once again, the worst thing to do is to plant trees, to deeply. Simply stated, to avoid girdling roots plant just a bit shallow, with the root flare slightly above grade.



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