(Note: This column isn’t about red Japanese maples)
Q. I have noticed several red maple trees in my neighborhood that are not doing well. One appears to be dead, with the bark flaking off, and the others have been colored up for fall for weeks already. I have enclosed photographs, and hope you can provide information to help save these trees.
A. The photos show a number of problems that started with improper planting or a change of soil grade after they were planted. The tree with the bark sloughing off is beyond help; the others are large and well established, and it may be too late to undo the damage. There are remediation practices that may help, but they are expensive and are not guaranteed. You will have to weigh the value of these trees against the cost of trying to save them. Removing them and planting new trees may be the most practical option.
The pictures show tree trunks that go straight into the ground like light posts or telephone poles. They may have been planted too deeply, or there may have been construction after they were planted that moved additional soil over their roots.
Sometimes trees come from the nursery with too much additional soil over their rootballs from cultivation between rows to maintain weed control. Now that most trees are dug by machine, rather than by hand, no one takes time to remove that soil. In that case, if they were planted by the old rule of thumb that says to “plant trees at the depth they were growing in the nursery,” they were planted too deeply.
Now we tell people to plant so that the root flare – the area at the base of the trunk where it flares out to meet the roots – is at the soil surface. When planting balled and burlapped trees, untie the twine that holds the burlap in place, pull the burlap back, and make sure the root flare is visible. If not, carefully remove the excess soil from the top of the rootball until you find it. It is not unusual for there to be three to five inches of excess soil, so keep looking until you find the root flare.
Trees that have been planted too deeply do not get enough oxygen to their roots. You may not think about roots needing oxygen since they are growing underground, but they need oxygen as surely as you and I. Trees often respond by producing adventitious roots. These are roots growing from stem tissue rather than root tissue. Over time, adventitious roots can grow in a circle around the base of tree and become girdling roots that literally choke off the tree’s ability to transport water and nutrients. Certain species of trees are more likely to produce girdling roots than others. Unfortunately, maples are at the top of that list.
Red maples are especially tough trees, adapted to growing in moist situations, which means that they tolerate low-oxygen soils. That is why these trees have grown for so long without obvious problems until now. One picture clearly showed girdling roots, and it would not be surprising to find the other trees have them as well. Girdling roots can occur below the soil line where they are out of sight. Another picture showed what looked like the top of a galvanized wire basket that is used around large rootballs to help hold them together. If the top few courses of wire are not removed when the trees are planted, the wire can girdle the lower trunk and larger roots as they grow in girth.
Trees that simply are too deep can sometimes be saved by crown excavation. An air spade is a tool that uses high volume, low pressure air to work up the soil around established trees without damaging the roots. Excess soil can be pulled back from around the trunk to permit the tree to grow at the proper planting depth. I have seen trees make a miraculous recovery after crown excavation.
Even girdling roots can be removed to allow affected trees to transport water and nutrients freely, depending on their size. If they have grown too large and impinged on the trunk too much, removing them is not an option. A certified arborist can assess the trees to see which, if any, are salvageable, and a number of local arborists are offering crown excavations.