Sunday, March 11, 2012

Pruning hydrangeas

I get a lot of questions about pruning hydrangeas. It can be a confusing topic because some hydrangeas are pruned differently from others. The process was baffling to me the first years I grew them but it turned out I did the right thing - I didn't prune them at all.

Ask yourself this - why do you want to prune your hydrangea? The only good reason for pruning is to control their size. If you have one that is getting too big for its britches or just getting in the way, then prune. However, there are certain rules to know.

First things first - do not prune at all until the hydrangea is at least 3 years old.

Hydrangea macrophylla - the mophead types - are the most popular and the most commonly grown hydrangeas. They bloom on old wood and new growth coming from old wood which means you should not be pruning them this time of year! If you cut them back now, you will be reducing your blooms. You can thin them out. To do this, take a look at the bare twigs and look for the oldest canes - they are easy to spot - they will be thick and have a gnarled appearance. Cut these canes completely down to the ground. The remaining canes should be left alone. If you are pruning a large macrophylla to reduce its size, then you can cut back the remaining canes to your desired height. Just keep in mind that you may not have as many blooms this year as you normally would.

An exception to this rule are the "Endless Summer" hydrangeas. They have the distinction of blooming on both old wood and new wood. They can be pruned without the danger of losing flowers.

This is Hydrangea "Ayesha". It is about 4 feet tall and, as you can see, new leaves are forming at the tips of the canes. This hydrangea does not need any pruning at this time. I'm happy with the size of it so I won't be touching it with the pruning shears.

This hydrangea "Madame Emile Moliere" also doesn't need pruning although it is covered with dry flower heads. The flower heads can be removed - just cut them off at the base of the bloom.
The same hydrangea with the flower heads removed.
The only hydrangeas that can be pruned back to the ground this time of year is Hydrangea arborescens and Hydrangea paniculata (aka PeeGee hydrangea).  The most popular one is "Annabelle". Unlike hydrangea macrophylla, these bloom on new wood. Therefore you can cut them way down to the ground and not worry about sacrificing flowers.


Hydrangea arborescens "Annabelle" before pruning

Hydrangea arborescens "Annabelle" after pruning
That leaves Hydrangea quercifolia, the Oakleaf hydrangeas. I've never pruned mine except to remove dead branches. If you need to prune to control size, they should be cut back late in the summer after they have bloomed.

If you'd like to hear more about growing, selecting, pruning and propagating hydrangeas, I will be doing a program at the Florence Lauderdale Public Library on Thursday, March 15th at 11:30. 

Text and photos by Phillip Oliver, Dirt Therapy

7 comments:

  1. I got out in the garden some this afternoon and dug up 6 or 7 volunteer Snow Queen Oakleaf Hydrangea under my big one, for transplanting along the dry creek. Last year I transplanted 4 along it. In a few years I should have a whole bank of them. Mary

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  2. Good instructions Phillip. Ihave all but my Oak leaf a good pruning this year. Last year some of the stalks stuck up above the green last year on some of them. I thought I would just give them all a good cut back since it has been so mild. I don't know if they realized we had winter. I barely have.

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  3. What a great post! I've already forwarded to two people! Wish Florence was closer!

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  4. I follow the never prune methodology, I am too concerned about screwing something up. Though while you're on the topic, I'd like to know if it actually helps Annabelle to be pruned?

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  5. Jess, I think the only advantage to pruning Annabelle would be to rejuvenate it or thin it out. In my experience, it always performs the same whether it is pruned or not.

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  6. Pruning hydrangeas is right up there with pruning clematis vines as far as confusion! I normally leave mine alone.

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  7. Great post Phillip. I only grow the paniculatas and 'Annabelle' because it is so hot here. However, some folks have long established hydrangeas which do well. I have never had luck with the Endless Summer type. I think it's our crazy weather. I pulled out my older mopheads because a late freeze often nipped their blooms. Thanks for the info.~~Dee

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