Our ten yr old Japanese maple is in the front garden, southern exposure, full sun. We’re in Toronto. It’s been a beautiful plant, but this spring it’s only producing leaves on the outer branch tips. I’ve trimmed it over the years but never done a serious pruning because I don’t know how. Is that the problem with it, or is it something more serious?
Acer palmatum, or Japanese Laceleaf maples, are susceptible to frost damage. The Toronto region had a cold winter and spring, and so it’s quite possible this is the reason that your maple is not leafing out properly. To provide care for your damaged tree wait a month or two to see if the tree starts to grow more leaves. After that, cut out any obviously dead branches to their point of connection. Provide the tree with adequate water, apply a slow release fertilizer and apply 3 to 4 inches of mulch around the base of the tree, taking care to leave several inches of space between the mulch and tree trunk. To help protect the tree from damage in the future, water the tree up until the first frost, and add an extra layer of protective mulch. This link will give you more information about how and when to prune your Japanese maple for health and shape.
Good luck with your tree.