Kousa Dogwood leafing out slowly

(Question)

Hello,
I have a three-year-old kousa dogwood that is leafing out at a snail’s pace – an erratic snail, if the truth be told. The tree has leaves top to bottom, though not throughout. About 50 percent of the buds have opened, while the remaining 50 percent are either just beginning to open or are closed up tight like it’s February. On some branches some of the leaves have opened while others are still closed, so it’s not like the entire branch is dead. Either way, the poor dear looks rather sparse for this time of year. Adding a tad more mystery to the matter is that the tree is flowering where it has leafed out – rather profusely, too. The tree is planted in a sun/shade site on the outer rim of a larger tree’s canopy. The soil is well drained (new bed several years ago made with triple mix) and lovely as it is topped off with compost each Spring. The site is partially sheltered by a fence on two sides and there is little competition root-wise for the tree. We are in zone 6 in Leslieville in downtown Toronto. Many thanks for any help you are able to offer.

(Answer)

Kousa dogwood (Cornus kousa) is a lovely flowering tree native to Japan and China. It is cold hardy in the GTA, but even so it may have been affected by the abnormal freezing and thawing we had over last winter. Many shrubs and trees have suffered die-back or had poor leafing out and flowering in the spring in the last two years because of the unusual winter temperatures. There are many examples of winter-related problems causing delayed or diminished blooming on dogwoods and magnolias.

What to do? The first step is to prune out any dead or damaged material once you’re sure that the stems have died back. Some shoots might look dead but still be alive. You can use a “scratch test” to see if there is green tissue under the bark. Then prune back to just above a live bud. That should help revitalize the tree and, it is hoped, allow it to bloom as usual next year.

However, there is another possibility that may be acting in conjunction with the cold winters. Is it possible that that the larger tree next to the Kousa dogwood is shading it more than it did in the past? Is there any evidence that the dogwood is stretching a little to find the sun?

If the cold winters and the diminished sunlight are working together to stress the dogwood, then another strategy might be to trim the larger tree or even move the Kousa out a little to a place where it will get more sun. That way it would be better armed against another cold winter.

For more information on the Kousa dogwood, see:

https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=j910