I planted this shrub three years ago and it only shows ONE bloom every year. It is in shade (as I thought it should be) – could that be the problem? I have not pruned it yet. Any idea ?
Thank you for contacting Toronto Master Gardeners.
Oakleaf Hydrangeas, Hydrangea quercifolia, are beautiful additions to the garden. You are correct, they do prefer shade and well drained soil.
Toronto is on the edge of the coldest zone they can tolerate. The flowers grow from buds that develop on old wood. Your plant is growing buds right now for next years flowers.
Unfortunately, the weather in Toronto does not always allow the buds to survive the winter. Freeze/thaws break the buds dormancy then cold temperatures kill the buds. Once damaged you will not get blooming the following year. Every few years the buds will survive the winter but there is no predicting when that will happen. Last year was not a good winter for them. There are many hydrangeas that bloom on new wood so develop their buds in the spring. The white ones you see around the city bloom on spring growth.
If you need to prune it, it should be done after blooming but before it starts setting buds for the following year (before the beginning of August). Pruning at this point would guarantee no blooms in the spring.
I have attached some links for further reading about Hydrangeas.