Does your hydrangea look like this?

The title say it all – this is the single most common question we receive about hydrangeas, especially this time of year. Thankfully, though the causes of this problem can be numerous, most of the solutions are simple! We’ve addressed some of the most common causes here.

Incorrect Pruning

This is the single most common cause of unreliable blooming in hydrangeas. First, a quick lesson:

Hardy hydrangeas can broadly be divided into two flowering categories: those that bloom on New Wood and those that bloom on Old Wood. The easiest way to figure out which category your hydrangea falls into is to look at the botanical (or scientific) name of it. (If you don’t have access to that information, give us a call and we’ll be happy to help figure it out for you!)

Plants that bloom on New Wood include Hydrangea arborescens and Hydrangea paniculata (known as ‘Smooth’ or ‘Annabelle-type’ and ‘Panicle-type’ hydrangeas respectively). These plants set their flower buds on newly-grown branches each year. This means you are safe to prune them early in the spring (preferably when they are still dormant).

Plants that bloom on Old Wood include Hydrangea macrophylla, Hydrangea quercifolia, and Hydrangea serrata (also known as ‘Mophead’, ‘Oakleaf’, and ‘Mountain’ hydrangeas respectively). These hydrangeas set their flower buds on last year’s growth. These hydrangeas should never be pruned if you can help it. No matter when you try to prune them, you’re likely to remove the majority of next year’s flower buds. If you must prune them, try to do so before the beginning of August, but be aware: even this can be a gamble.

Some newer Mophead Hydrangea cultivars bloom on Old and New Wood, so even if you do prune you’ll receive some scattered flowers, but to maximize your flower count, you’ll want to put the pruners away.

Old Man Winter

Sometimes Ontario winters are bitterly cold, and though our hydrangeas may survive, the flower buds they have set for next year may not. Cold winters or late frosts can reduce your hydrangea’s bloom count. Many of the hydrangeas sold around Easter as an indoor plant will survive if planted outside but will never produce flowers for the same reason – their buds will be injured by our winters.

Too Much Nitrogen

High-nitrogen fertilizers tend to create beautiful, lush dark leaves, and few to no flowers. If you think your hydrangeas need fertilizing, use one with a higher middle number, as this promotes flower production. If you’re applying high-nitrogen fertilizer nearby for a lawn or evergreen, you may be inadvertently fertilizing your hydrangea as well.

Improper Lighting

Most hydrangeas can tolerate (and most mopheads/oakleafs prefer) part shade locations, but particularly shady locations may reduce flower production. Consider transplanting hydrangeas in dark, deeply shaded areas to a location that receives a bit more light.

Still struggling with your hydrangea’s flowers? Don’t worry – we have more solutions here in our Hydrangea Care Tipsheets.