Japanese Maple


Dear friends, I am hoping you can help me identify what happened to a mature japanese maple, and if there is any course of action that I can take to help it out. This tree, in Stratford, Ontario, is about ten years old…well established, beautiful and healthy up until this year. In the spring we noticed that the bark at the base was damaged….just not sure how…the gash seems to be growing and we found a caterpillar in the crack this past weekend (this damage does not appear to be as a result of freeze/thaw and sap flow). The tree seems to be very stressed and the leaves are curling up and browning from the tips. Please help!



Thank you for writing, and how unfortunate that your Japanese Maple, Acer palmatum, is suffering. This is a very timely question, and may be pertinent to numerous gardeners, considering the current availability, and popularity, of many varieties of Japanese Maples. Among the reasons for your tree’s cracked trunk, you should consider: freeze — followed by sudden thaw damage, insect damage and sun scald damage. Any, or combination of, the above conditions could be affecting your tree. The very best advice is to contact an arborist for a diagnosis as soon as possible, and here is the link to Landscape Ontario’s site where you can readily locate a professional to make a house call: https://www.landscapeontario.com.

This past winter, in southern Ontario, was particularly harsh, not so much due to heavy snowfall, but more so due to several thaws, follow by an immediate return to the deep freeze. This can often cause tree trunks to split. You mention that the split does not appear to be a result of extreme temperature shifts, but it is still well worth considering. And finding a caterpillar may just be a sign that insects and pests gravitate to areas of weakness in plants. The best news, on a split in the bark, is the formation of “callous” rolls, an indication that the problem has been stopped, and the sealing of the injured area has begun. Sealing, or compartmentalizing, refers to tissue damage containment, not replacement.

Finally,  JM’s like a combination of full sun, to part shade, every day, and it’s possible that when your tree was smaller, it may have received more shade than it’s receiving now, assuming it has grown taller and broader each year. And, last summer in your area was particularly dry over an extended period, and, if you were not watering your maple with two large watering cans full every three days, it may have been stressed, even then, from a lack of water. You report that “leaves are curling up and browning from the tips”, and the bark on your image does seem to be very dry and brittle, so you might consider starting this regime immediately, so as least to alleviate drought issues as one of your tree’s problems.

Also adding a link to our Toronto Master Gardeners Guide on Japanese Maples: https://www.torontomastergardeners.ca/gardeningguides/growing-japanese-maples-a-toronto-master-gardeners-guide/

Thank you for this opportunity to help with your tree’s issues, and hoping that you can restore it to good health!