Pruning hydrangea paniculata

I have 5 new paniculata vanille fraise. They aren't very strong yet and has bloomed with massive heads that are weighing the plant down. I've done a search and can't find a definitive of when to prune. There seems to be loads of advice out there for every other hydrangea apart from paniculata! I leave my macrophylla till Spring but wondered if it would be OK to prune the paniculatas as soon as it stops flowering.

 

All the paniculata types are pruned (if need be) in February. They flower on new wood, that is growth made in the same season. So you are not removing flower buds when pruning early in the year.
Personally I have never bothered as I wanted them to get big, only removing any damaged stems.
Finished flowers may be removed once they are over and done with to keep the bush safe over winter, avoiding wind damage etc.

 

You have some flexibility with paniculatas. They develop flower buds in Spring and these then open either in late Spring or sometime in the Summer months. As a result, you can deadhead any time after they bloom but before they develop their invisible flower buds (safest if you prune before early/mid Spring). So for example, you can enjoy the flowers until they turn brown... or enjoy the flowers before then: some people do not like the shades of pinks or paniculatas' propensity for flopping so they deahead the large panicle shaped blooms quickly.

Note that deadheading is not the same as pruning:
Pruning Hydrangeas | Plant Addicts

I typically let Mother Nature take care of this task although sometimes, you do have to deadhead the flowers yourself. The peduncle string of paniculatas and oakleaf hydrangeas tends to be very thick so it can support the weight of blooms and thus it will not quickly decompose. As a result, I can get blooms by late Spring and the dried out blooms will sometimes be sticking around a year later!

Macrophyllas and serratas (mopheads an lacecaps) are slightly more complicated. Typically, they produce invisible blooms at the ends of stems by the end of Summer or the start of Fall. I find that if I need to prune, cutting after they bloom but before the Summer Solstice is best. The late Summer/early Fall flower buds from last year open in Spring so if you prune after they have developed, then you cut off Spring blooms and get less blooms or no blooms the following year. That scenario -for example- describes what is meant by mopheads that bloom on old wood. But there is another scenario.

Many of the newer macrophylla/serrata introductions bloom on old and new wood. They are called rebloomers but they are actually remontant. That means that completely new and green stems that start growing in the Spring will develop flower buds in late Spring/early Summer and the buds will open and produce flowers by late Summer or early Fall. This works fine as long as the new stem growth has a chance to become old and tall enough to produce buds and open the flowers. And as long as you do not cut the new stems after they develop flower buds. Thus, I try to be careful when pruning my remontant macrophyllas. It is best not to prune them at all period, except for deadheading or cutting dead stems. Better yet: if you plant any type of hydrangea in a location where it can attain its estimated height/width at maturity on the plant label, you should not have to prune to maintain the hydrangea size under control. You would have to deadhead spent blooms and some dead wood only.

 

Thank you so much @luis_pr that's really helpful. I'm going to deadhead the paniculata when it finishes blooming because they're all lying on the ground anyway. I didn't expect such young plants would have such massive blooms!

 

You're wwelcome. Yes, some paniculatas do have large blooms and a few don't. Pinky Winky does best as far as blooms not flopping but its bloom form is lighter in form, weight and size. Compact ones may also flop less but it is always best to look at the blooms near the end of the growing season to see how do they perform. Enjoy your Pink Diamonds.

 

I have a hydrangea paniculata for 2 years. It blooms beautifully last year. I don't know what overcame me, but I have hard pruned it way too early, before the winter ( I am obviously a novice). Luckily it has survived as the bark is green but zero growth till now! Have I murdered the plant? Is there anything I can do? Will it just die slowly? (Sob sob) Any advice is appreciated.

 

It'll be fine.
I can see you've tested the bark and there is green,so it's alive.
As in the thread above, they flower on stems produced in the same year.
The roots will still be good, so it'll likely leap into growth soon and you may even get some flowers this year.

Have a look at P4-5 for pruning -
https://www.rhs.org.uk/plants/pdfs/plant-trials-and-awards/plant-bulletins/hydrangea-paniculata.pdf

 

I hard pruned a couple of mine before winter to a slightly higher height and they are starting to leaf up nicely. I added a few handfuls of blood fish and bone at the bases in late February. You could also do that now, just move the bark aside first and then replace it and keep the plant well watered.

 

Do not expect a quick bounce back unless it is actively growing. Overnight soil temperatures above 10°F also help.

 

Thank you all for your tips. I have put a handful of blood and fish bone. Fingers crossed!