I purchased a plant at a yard sale and was told it was a Hydrangea macrophylla. I have had it in different areas of my yard with varying degrees of sunlight. I’ve trimmed it in the fall, or not at all and have never seen it bloom.
Thank you for contacting Toronto Master Gardeners.
It is not unusual for there to be issues with this type of hydrangea not blooming.
Some hydrangeas bloom on new wood so the blooms you see are on the current growth the plant has developed this season. The plant you have blooms on old wood, so growth from previous seasons. We are at the northern edge of the range for this plant so in most winters the old growth and buds are damaged or killed by the low temperatures. The plant is then unable to flower the following season. Certainly trimming the plant in the fall will remove any flower buds the plant has developed for the following year. Perhaps wrapping the plant and giving it some winter protection would help.
I am including a link below for further reading.