Japanese Maple With Swollen Trunk


Hello, I have a red, bloodgood ,Japanese maple tree that is about 15 years old, and 14 ft. in height. There is a swelling around it’s trunk, about a foot above ground, with some small vertical cracks in the bark in this region. I noticed it for the last couple of years. The area is firm to touch, and the bark is hard. There are some small white patches in this area that appear to be lichen. Last spring, there were less number of leaves than usual, and lots of flowers, they had to be raked up from the grass around it, several times. I also noticed many small dead branches. Should I fertilize this spring? If so, which fertilizer should I use? Is my tree diseased?
Thank you.


Thank you for contacting the Toronto Master Gardeners. It is always distressing when we see a tree that we have nurtured and loved for 15 years not preform as expected.

Without a photo of the injury or where it is located it is difficult to pinpoint exactly what is wrong with your Japanese maple.

Is the bulge around the root flare of the tree? The root flare is the portion of the tree where the trunk widens at the base as it transitions to the root system. Many ornamental Japanese maples are grafted onto a rootstock of a hardy, less ornamental Japanese maple. You can always see where the graft is by looking for scars and a thickened area on the trunk. Another possibility is that the tree suffered damage due to rodents chewing on the bark or if the tree is planted in the yard could the base have been damaged with the lawn mower or weed wacker?

Trees respond to wounding or injury by forming specialized “callus” tissue around the edges of the wound. Thus, the tree responds to the injury by “compartmentalizing” or isolating the older, injured tissue with the gradual growth of new, healthy tissue. Not only do trees try to close the damaged tissue from the outside, they also make the existing wood surrounding the wound unsuitable for spread of decay organisms. Often a raised area of “callus tissue” will develop in the tree’s attempt to close the wound.  However, even a slight opening may be enough to allow insect pests and fungal diseases to infest or infect the tree.

You mentioned that you had fewer leaves last spring. Did the leaves shrivel up prematurely? Did you see wilting of leaves on only one side of the tree? It could be that the tree is suffering from verticillium wilt. Verticillium wilt is a fungal disease caused by soil-borne pathogens Verticillium dahliaeand V. albo-atrum. This fungus enters the cambium layer of the plant through the roots or injured areas on the trunk and blocks the flow of nutrients within the tissues. This leads to dryness and wilting in affected twigs. Early indications that a tree has Verticillium wilt include heavy seed production, leaves that are smaller than normal, and the browning of the margins of leaves. The following link provides more information on this disease : https://extension.psu.edu/verticillium-wilt-of-woody-ornamentals

To check if your tree is suffering from this disease check the sapwood located under the bark of wilting branches. There will be brown streaking in the sapwood and in cross section an infected branch will show a dark ring or pin-point dark spots. There is no cure for this disease. Prune out damaged areas. Be sure to sterilize pruners with a 10% solution of household bleach between cuts and avoid moving soil or debris from an area of known infection.

According to Landscape Ontario landscapeontario.com/japanese-maplesOnce established, Japanese maples may be lightly fertilized only in the early spring (April) with 4-12-8 fertilizer or 15-30-15 water soluable mixture. Major structural trimming may be done before the new leaves unfurl in spring. Lighter pruning can be acomlished any time in June after the first major flush of growth begins”.

The best defense here is to use good cultural practices to ensure your tree is the healthiest it can be:  make sure you water your tree during drought conditions, avoid compacting the soil around it, remove leaf debris in the fall, and amend your soil with organic fertilizers (compost) and mulch (not touching the base of the trunk but in a circle around it).

As the tree leafs out this spring look for the leaves beyond the swelling to wilt, the bark to crack, and/or for signs of weeping of sap. You might want to have the tree examined by a certified arborist if any of these signs develop

The Ontario chapter of the International Society of Arboriculture’s website can help you to locate a qualified arborist in your area:  https://www.isaontario.com/  He will be able to determine the best course of action to help maintain the health of your Japanese maple.