I live in Toronto.
Can I trim limelight hydrangea by 1/3 now, May 8?
They do have some buds appearing.
Or is it too late? Should I wait until fall?
Limelight hydrangea is a type of “panicle” or “PeeGee” hydrangea (Hydrangea paniculata). These are available in shrub and tree forms and this variety will start off with lime green, conical flower clusters that turn pink with age.
Panicle hydrangeas flower on new wood, meaning the buds form on branches produced in the current growing year. Pruning of these cultivars should be done in late fall or late winter before new growth begins. Spring pruning may remove the flower buds produced on new branch growth.
If pruning is done before the new growth appears, you can prune them all the way down to above one healthy bud union on each stem and you can also prune down any main branch that you want to keep small. Strong new growth will appear where these cuts are made. It will produce much larger blooms if pruned hard like this each year. Some gardeners prefer to leave a framework of 30-60cm old growth to reduce flopping. This may result in smaller blooms but on sturdier stems. Pruning no more than one-third of any stem is the general guideline for all pruning.
The Toronto Master Gardeners get many questions about hydrangeas. On the home page of our website, type ‘hydrangeas’ under ‘Find it Here’ to see a list of previous questions on this topic. You may also be interested in our Toronto Master Gardeners Growing Hydrangeas Guide.