What is the Hydrangea Danger Zone™?
Right now you and all other gardeners who grow hydrangeas could be in the Hydrangea Danger Zone. It’s that time between the fall when your “old wood” hydrangeas set their flower buds, and the coming spring when those buds emerge. That is if they have made it through the winter.
But what makes it so dangerous, you may ask. We, the gardeners! We want to get outside at the first sign of warm weather and start pruning our plants. Therein lies the problem. If you cut your old wood hydrangeas now before you see those new buds, you could actually unwittingly remove those buds. Then all you will have is a nice green bush – Mon dieu!
The Key is to Know Which Hydrangeas Flower on Old Wood
So you need to figure out which of your hydrangeas flower on old wood. Those are the stems that have the flower buds you want to protect from pruning cuts. I can help you with that.
If your flowers are cone-shaped and change color from white or cream to shades of pink and rose, and the leaves look like an oak leaf, that’s an oak leaf hydrangea (quercifolia). Oakleaf hydrangeas always flower on old wood.
If you’re lucky enough to have a hydrangea that’s a vine, that’s a climbing hydrangea (anomala petiolaris)
which also flowers on old wood.
which also flowers on old wood.
If your flowers are round and blue, that’s a big leaf hydrangea (macrophylla), an old wood flowering plant or a mountain hydrangea (serrata). Newer cultivars like Endless Summer bigleaf hydrangeas and Tuff Stuff mountain hydrangea are remontant, meaning they bloom on old and new wood.
Those flowers can also be somewhat flat and even lacey-looking. This lacecap flower can be on your big leaf (macrophylla) or your mountain hydrangeas (serrata). Lacecap flowers can come on plants that flower on old wood.
But what if you have a plant with round flowers that are white and don’t change color? That’s also a big leaf (macrophylla) hydrangea.
If it doesn’t change to blue and stays some shade of cream or pink, it could be a woodland/smooth hydrangea (arborescens) like ‘Annabelle.’ The foliage will confirm which it is so check it out to be sure.
Exactly What You CAN Cut Now
Any of your purely new wood bloomers can be cut and trimmed now. That means you can take care of your panicle and woodland plants. No worries since their flowers this year will come from the growth they put on in the spring. In fact, pruning cuts can stimulate them to produce more flowers.
What Plants Should I Leave Alone?
Leave your oakleaf and climbing alone unless you have dead, diseased, or damaged wood that needs to be removed.
Try your best to leave your big leaf and mountain hydrangeas alone as well. Those old wood flowers will start to show their buds soon. The best thing you can do is wait for your plant to break dormancy. Then inspect it for those tiny little buds called “broccoli”.
If your plant has outgrown its allotted space and you don’t care about losing flowers, then cut away. I would personally prefer to first get the flowers this season and then cut it back before August 1.
Do I Treat Rebloomers Differently?
We already know that reblooming big leaf hydrangeas can flower on new wood, but don’t think that rebloomers flower ONLY on new wood. Au contraire, rebloomers have both old and new wood genetics. And those old wood buds are waiting to come out and play. They, therefore, need to be protected from premature pruning.
If it’s a rebloomer, it’s even safer to wait until you have passed your last frost-free date. That’s because
rebloomers can give you a second season of flowers as long as those sleeping buds haven’t awakened. Sometimes when we cut before that last frost-free date, the reblooming buds start swelling as spring temps warm-up. Then they get zapped by a late-season weather event like snow or ice. I speak from experience.
rebloomers can give you a second season of flowers as long as those sleeping buds haven’t awakened. Sometimes when we cut before that last frost-free date, the reblooming buds start swelling as spring temps warm-up. Then they get zapped by a late-season weather event like snow or ice. I speak from experience.
The Wisdom of Doing Nothing
You are left with a couple of options for big leaf and mountain hydrangeas: do nothing which is fine and more than acceptable. Or you can wait to see those buds and do everything you can to protect them if ol’ man winter comes back one more time.
If I Can’t Prune, Exactly What Else Can I Do?
Scratch that gardening itch by cleaning up your gardening tools and sharpening your pruners. Not only will you feel holy but you’ll be ready for the right time when you can confidently cut your old wood plants safely.
Now, do you see why I call it the Hydrangea Danger Zone?
Written By: Lorraine Ballato
Author of: Success With Hydrangeas: A Gardener’s Guide
“This post on Hydrangea Danger Zone is provided as an educational/inspirational service of the National Garden Bureau and our members. Please credit and link to National Garden Bureau and author member when using all or parts of this article.”
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3 comments. Leave new
We moved into our house in the Fall about 30 years ago. At that time, we were told that a massive bush in the back was a beautiful. We seems to get the ‘broccoli’ every year but no flowers. Not knowing anything about them, I’ve pruned it at various times. I’ve also left it unpruned for a couple years in a row. Nothing seems to work. What might I be doing wrong? At the time we moved in, the bush was in the shadow of a 40′ weeping willow which we had to remove. Now the bush gets sun pretty much all day. Could that be the reason?
We asked Lorraine Ballato, author of this article, and she said…
First of all, you can be sure your plant was a hydrangea that flowers on old wood. That’s the growth it put on last season. So that means no pruning at all (which you have already practiced), or pruning only after you see “broccoli.”
If you are getting “broccoli,” you should be getting flowers from those buds. The only thing I can think of is water (excess or stress) might be robbing your plant of the energy it needs to turn those buds into flowers. The second possibility is soil fertility. Somehow your plant just doesn’t get enough to make those buds into a flower.
That being said, 2 things you can do: first, do a soil test and see what you are working with. If you need to fertilize/amend, use a granular slow-release product made for shrubs. Rose food is ideal. Follow the directions on the label.
The second action is a little more involved. Stick your finger in the ground around the base of your plant, going outward to the ground below where the stems extend (that is called the “drip line”). If it is dry at your second knuckle, your plant needs water. Test and retest regularly to see how often you get that result. You may have to add more compost and mulch to help your plant retain moisture better. You mentioned your plant gets sun pretty much all day. So if you are in the southern states, that sun may be frying your plant and causing water stress.
You could also move your plant to a place where it gets only a half-day of sun and give it some relief. Or you can plant something close enough to provide shade without creating root competition. I put in a ‘Bloomerang’ Lilac to provide that necessary afternoon shade. The lilac grows quickly, stays small enough to easily manage, repeat blooms, and protects my hydrangea from the afternoon sun. There are lots of plants that can do this for you.
If that second knuckle is wet and you have had no rain, the plant might be getting TOO MUCH water. Hydrangeas love water to the extent that they make leaves instead of flowers when they get a lot of it. Test and retest regularly to see how often you get this result. Then you may have to back off your irrigation if you have it, or amend your soil to be less water retentive, or move the plant to a site that doesn’t drain so quickly.
In my best-selling Success With Hydrangeas book, I discuss the many ways you can grow this magnificent shrub. You might also get some pointers from my hydrangea blog.
Very good article, thank you. Well explained, good photos, easy to follow