Recently, several questions related to pruning different trees and shrubs have come to my inbox or have been posted to our Discussion Board. One of these questions was regarding Endless Summer hydrangea.
I have 7 Endless Summer Hydrangeas that did not bloom at all this year. In previous years, I had tons of blooms, so I did something wrong when I pruned them. I can’t remember what time of year it was the last time I pruned them, but I have not touched them at all this year. They are lush and green and growing, but no flowers. When should I prune them to ensure flowers next spring and summer? I live in Southern NH, about 50 miles north of Boston.”
Hydrangea macrophylla, which includes the mophead and lacecap hydrangeas, normally blooms on “old wood”; that is, growth that was produced in the previous season. At the northern edge of their hardiness range, the flower buds of these hydrangeas, which are formed in August and September, are sometimes damaged or killed during severe winters. This means few or no blooms the following season. This happened to my lacecaps this year. In addition, if these shrubs are pruned at the wrong time (in the fall or spring), all those flower buds will be removed and oops – again, no flowers!
The Endless Summer Series is a unique group of Hydrangea macrophylla that blooms on both old wood and new wood. How cool is that? They are also hardier than lacecaps and other mopheads, surviving and blooming even as far north as Zone 4!
If the flower buds that are produced in the fall are killed during a severe winter, no problem! These Endless Summer hydrangeas will still bloom later in the summer, since they readily produce flower buds on the current season’s growth. Because of this trait, they normally flower reliably every year regardless of winter severity.
Why didn’t they bloom? That’s a good question but I suspect that it is not an issue of improper pruning. Regardless of how you prune these shrubs (unless you keep whacking back the new growth all summer), you should still get at least some summer blooms as long as they are healthy, get enough sun, and are fed and watered properly.
The problem here is more likely to be related to nutrition. Since these shrubs have lush leafy growth, it seems that they are healthy and growing well – perhaps too well. If a flowering plant receives too much nitrogen, it will grow like gangbusters and “forget about” producing flowers. This is what you want for your grass – not your flowering plants.
In fact, this is sometimes what happens when flowering trees and shrubs are planted in the lawn rather than in designated flowerbeds. Your lawn is fertilized with a high nitrogen fertilizer so it grows lush and green but guess what? If your flowering plants are growing in the lawn, they are getting the same high nitrogen food. What’s their response? Grow lots of foliage and no flowers! The nutrient responsible for flower bud production is phosphorus, an element that has recently been removed from most lawn fertilizers.
I have no idea if this is the situation for these particular Endless Summer hydrangeas, but regardless of where they are growing, these shrubs may just need a shot of phosphorus in order to initiate flower bud production. A bloom booster fertilizer or Espoma Triple Super Phosphate (0-45-0) might do the trick. I suggested that she feed them with a good quality organic fertilizer such as Espoma Holly-tone plus an application of Super Phosphate according to the label directions. Hopefully, this will help and her Endless Summer hydrangeas will bloom next season.
How and when DO you prune Endless Summer hydrangeas?
The best time to do any structural pruning is just after they finish their initial bloom in early summer.
In the spring once the new leaves have fully expanded, any branch tips that were killed over the winter should be pruned back to live wood. In more northern areas, this may mean more extensive pruning and the loss of the early bloom.
When the first blooms fade, do any necessary pruning to reshape or reduce their size or just deadhead the flowers. This pruning will stimulate new growth and the formation of flower buds for the summer rebloom. Deadhead the flowers throughout the summer to encourage the production of additional blooms. You can even cut flowering stems for indoor arrangements and this will stimulate the production of more flowers!
All pruning of Hydrangea macrophylla, including the Endless Summer varieties, should be completed by the end of July because after that, in August and September, the flower buds for the next season’s early bloom will be forming.