This is the most frequent question I’m asked on my radio programs, and lately I’ve been getting several emails a day as well. We love the blue mophead and lacecap hydrangeas, so it’s upsetting when there are no blooms! Here is what’s going on.
First of all, it’s important to know that these plants produce their flowers on old wood. What is old wood? This just means that in the late summer the plants form flower buds on the canes that will bloom the following year. You can’t see them, but the germ of next year’s flowering is already on the canes in the fall. This is the reason that it’s important not to cut Hydrangea canes back in the autumn (remember: Don’t Fall Down!) or in the spring. For pruning information, see this article.
In addition to inappropriate pruning, the main cause of these Hydrangeas not blooming is cold winter or early spring temperatures. If the temperatures drop into the single digits for very long, those flower buds get zapped. If the buds are swelling in the early spring, and the temperature drops into the 20’s, they are also killed. And if the temperatures go below zero fahrenheit at any time, your mophead and lacecap hydrangeas won’t flower the following year.
The winter of 2015 and 2016 was a “hydrangea flower killing winter” because of two things. First of all, it was mild, mild, mild for a long time. My husband and I walked on the beach in short sleeved shirts on Christmas day! But then, after such warm weather it suddenly dropped below zero over one weekend in February. That killed off many hydrangea flower buds. And many that made it through that period got zapped later in the spring. We had a very warm March in the Northeast, and many hydrangea buds started to swell and break dormancy. Then the second week in April the temperatures dropped into the 20’s, killing off any remaining flower buds.
Some people who are in warmer locations (closer to the ocean) or have their plants in a warmer micro-climate in sheltered spots, still have fair to good flowering. But many have no flowers at all.
If your Hydrangeas are the type that also flower on new growth (Endless Summer, Penny Mac, All Summer Beauty, BloomStruck etc) you’ll have some flowers later in the summer or early fall. And those Hydrangea species that bloom on new growth – H. paniculata varieties such as LimeLight, and H. arborescens types such as Annabelle – will flower as always.
What can you do for next year? Remove all dead canes. The ideal time to do this is in late May (see pruning sheet) but it can be done any time. Next, don’t cut your shrubs back this fall. Keep them deeply watered less often (usually every 5 to 7 days – water with a sprinkler, not by hand) and give them an application of an organic fertilizer in the spring. Note that wrapping doesn’t usually help unless you can erect a wind-barrier in exposed locations. The hydrangeas that I carefully wrapped with burlap and piled salt-marsh hay over the canes didn’t do any better than those that had no protection at all.
Finally, pray for a mild winter!