When and how to prune hydrangeas

How and when to prune hydrangeas — *Hydrangea macrophylla* flowers on old, second-year wood. (Photo by Joanne Young)

Margaret in Kingston, Ont., asks:

I have just read an article on hydrangeas, saying that some hydrangeas flower on the old wood? Eureka! Is pruning mine back each spring the reason why the bush has luscious green growth, but no flowers? In spring there are dead-looking buds on the branches from which flowering growth comes, but should I then be protecting the bush in the winter so that these buds are still viable to burst out in the spring? How do we know which kind of hydrangea we have? This bush originally had large dark pink flowers which matured to a deeper autumnal red in the fall.

Judith Adam, horticultural consultant for Garden Making says:

It would be helpful to know which species of hydrangea you have, as each has a different flowering pattern. If your hydrangea was received as an Easter houseplant gift meant for indoor display, it’s probably bigleaf hydrangea (Hydrangea macrophylla), which flowers on old, second-year wood. That species is root-hardy in Zone 6, but the canes with flower buds for the next year are not always hardy (sometimes frost will kill the canes). If this is your kind of hydrangea, then spring pruning would cut off the flowers for that season. Your dark pink hydrangea could also be one of the new bigleaf cultivars bred for gardens and hardy to Zone 5, such as red ‘Color Fantasy’ and dark pink ‘Forever Pink’, both blooming on old wood. It’s best to prune macrophylla hydrangeas as little as possible, but if necessary, try to remove only the third-year wood (wood that carried flowers last year). It’s easy to be confused about how old each cane is, and if space is an issue it might be better to grow dwarf marcrophylla hydrangeas that seldom require pruning, like the CityLine Series 20 x 20 inches (50 x 50 cm). There are three in this series: deep pink Cityline Berlin; red Cityline Paris; and pink Cityline Vienna.