Am I right in thinking that...
After the Hydrangea has finished blooming, it is habitual to leave the "mophead" flowers to protect the plant during winter
New buds will emerge on the stems that have flowered that year, to flower next year once the plant has been pruned?
New stems will emerge from the crown as well, beginning in the flowering season and into the autumn, which will bear flowers next summer (hence the saying that H. macrophylla flowers "on old wood?)
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luis_pr
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Hello, z. You can leave the spent flowers to add some winter interest in the garden but, leaving them will not protect the plant from winter in a measurable way. If you do not like the look, you can dispose of the spent blooms (this is called deadheading) in several ways. For example, you can use them as mulch, you can dye them to make arrangements or you can add them to the compost pile (but if the shrub suffers from some form of fungal infection on the leaves, dispose in the trash instead).
Flower buds develop starting around July (in the South... later up North). They are invisible at first and the shrub will bloom with these guys all way in Spring.
Pruning in July or later is not recommended so you do not miss out on the first flush in Spring. If you prune a hydrangea that blooms on old wood after the flower buds have developed, you will sacrifice bloomage for a whole year. But if the hydrangea is a rebloomer (like Endless Summer), you only sacrifice the early Spring blooms (you will get blooms later).
Macrophyllas that rebloom develop new buds around July too, have their first flush of blooms in Spring too and then, some time after the first flush, they begin to develop flower buds and flower again. Exactly when varies. Say, about a month after the first flush? These reblooming episodes reoccur several times and can be promoted by deadheading flowers. The longer your growing season is, the more reblooming episodes you can have.
New stems in Macs will usually produce blooms on year two but there are some varieties that will do it on year one. Some people have reported that their Nikko Blue stems do this (NB blooms on old wood).
Flower buds develop starting around July (in the South... later up North). They are invisible at first and the shrub will bloom with these guys all way in Spring.
Pruning in July or later is not recommended so you do not miss out on the first flush in Spring. If you prune a hydrangea that blooms on old wood after the flower buds have developed, you will sacrifice bloomage for a whole year. But if the hydrangea is a rebloomer (like Endless Summer), you only sacrifice the early Spring blooms (you will get blooms later).
Macrophyllas that rebloom develop new buds around July too, have their first flush of blooms in Spring too and then, some time after the first flush, they begin to develop flower buds and flower again. Exactly when varies. Say, about a month after the first flush? These reblooming episodes reoccur several times and can be promoted by deadheading flowers. The longer your growing season is, the more reblooming episodes you can have.
New stems in Macs will usually produce blooms on year two but there are some varieties that will do it on year one. Some people have reported that their Nikko Blue stems do this (NB blooms on old wood).
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luis_pr
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Some new stems will flower on the same year but not all hydrangeas do that; I actually saw the opposite with mine when I once marked existing stems and failed to remove the markers for one year. And yet some people have sworn their shrubs actually did so go figure. It depends on the variety. Do an experiment with your shrubs this year to find out what happens in 2011. Mark the existing stems now somehow and make a note in a wall calendar to remind to check what happened in the Fall of 2011.
Thanks.
I'm not so much interested in whether they re-bloom in the same year, but more as in where next year's buds come from...ie, if the H. blooms in summer 2010, when and where will the buds for summer 2011 come from...
The stems of the flowers that have just faded?
New stems from the crown (growing in 10 and into 2011)
Both?
I'm not so much interested in whether they re-bloom in the same year, but more as in where next year's buds come from...ie, if the H. blooms in summer 2010, when and where will the buds for summer 2011 come from...
The stems of the flowers that have just faded?
New stems from the crown (growing in 10 and into 2011)
Both?
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luis_pr
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A stem that produced blooms will produce blooms again the following year unless they are pruned. Most hydrangeas will bloom on terminal blooms but some -Dooley, Mme Emile Mouillere and Gen. Vicomtesse de Vibraye- can bloom in late Fall from lateral blooms when the terminal blooms are pruned in early Spring. Unusually cold weather or lack of moisture during winter could also kill flower buds. New stems will usually produce blooms on year two.
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luis_pr
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Hello, z. Gosh, I cannot believe I am awake in the middle of the night (here) but the dogs had to go outside... And now I cannot go back to sleep while they sleep all around me. 
Regarding your question as to whether you need to prune a hydrangea in order to make it bloom, the answer is no, not really.
If a Macrophylla hydrangea is planted in a location where it can grow to its "size at maturity", it should rarely require pruning. For example, my 6-8 year old house already had some unnamed varieties of macrophyllas and I have only had to prune one of the hydrangeas once. Since moving here, I have planted new Macs and have not had to prune those 3-5 year olds either.
By the way, "size at maturity" is a commercial term used here that gives you an idea of the plant height and width at 10 years. It does not mean that the plant stops growing when the hydrangea reaches its size at maturity.
Now pruning is not the same thing as deadheading, in which spent blooms are removed. This is usually done during the winter season on old/new wood hydrangeas but you can also do it at other times if you have reblooming macrophyllas. Deadheading of reblooming macrophyllas encourages more new blooms if done during the blooming season.
So prune if you want to remove dead or diseased stems. Prune for safety reasons too; say, the growth bothers people in high traffic areas. Prune if you want to improve the shape of the plant; say, by increasing air flow or light to certain areas of the plant. Also, prune if you want to produce less but larger flowers. Finally, you can prune to rejuvenate an old bush when it develops a habit of producing fewer or smaller blooms. In this last case, you can prune the hydrangea stems in thirds. On year one, prune the one third oldest looking stems to the ground. On year two, prune the next oldest third and, one year three, do the last third.
And do not worry much about which stems bloomed this year or not. The only time this would come in handy is if you are propagating by cuttings. Propagation is more successful if the stem did not flower this year.
Good questions, z!
Regarding your question as to whether you need to prune a hydrangea in order to make it bloom, the answer is no, not really.
If a Macrophylla hydrangea is planted in a location where it can grow to its "size at maturity", it should rarely require pruning. For example, my 6-8 year old house already had some unnamed varieties of macrophyllas and I have only had to prune one of the hydrangeas once. Since moving here, I have planted new Macs and have not had to prune those 3-5 year olds either.
By the way, "size at maturity" is a commercial term used here that gives you an idea of the plant height and width at 10 years. It does not mean that the plant stops growing when the hydrangea reaches its size at maturity.
Now pruning is not the same thing as deadheading, in which spent blooms are removed. This is usually done during the winter season on old/new wood hydrangeas but you can also do it at other times if you have reblooming macrophyllas. Deadheading of reblooming macrophyllas encourages more new blooms if done during the blooming season.
So prune if you want to remove dead or diseased stems. Prune for safety reasons too; say, the growth bothers people in high traffic areas. Prune if you want to improve the shape of the plant; say, by increasing air flow or light to certain areas of the plant. Also, prune if you want to produce less but larger flowers. Finally, you can prune to rejuvenate an old bush when it develops a habit of producing fewer or smaller blooms. In this last case, you can prune the hydrangea stems in thirds. On year one, prune the one third oldest looking stems to the ground. On year two, prune the next oldest third and, one year three, do the last third.
And do not worry much about which stems bloomed this year or not. The only time this would come in handy is if you are propagating by cuttings. Propagation is more successful if the stem did not flower this year.
Good questions, z!
Thanks for that, and I hope my questions did not keep you up too late. Seems to be just you and I posting on this...I'm not growing H's at the moment, but I am a student of Horticulture approaching an exam, and it is the theory behind this particular issue that I'm interested in.
I suppose to break down my question very simply, it amounts to this:
We are looking at a Hydrangea macrophylla, in summer, in flower.
Are there some stems arising from the ground which do not have flowers, only leaves - and which will bear flowers next year?
On the flowering stems, are there buds which will grow into branches this summer or through the autumn and will flower next year?
Or both?
So you see, its not so much practical advice I'm after, but a basic theoretical point.
I suppose to break down my question very simply, it amounts to this:
We are looking at a Hydrangea macrophylla, in summer, in flower.
Are there some stems arising from the ground which do not have flowers, only leaves - and which will bear flowers next year?
On the flowering stems, are there buds which will grow into branches this summer or through the autumn and will flower next year?
Or both?
So you see, its not so much practical advice I'm after, but a basic theoretical point.
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luis_pr
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Both. Both can bloom the following year. If you prune after the stem blooms but before flower buds develop, the old wood macrophylla stem can bloom. Same for the stem with only leaves. But as you can obviously observe in some hydrangeas in the garden, some stems will not bloom sometimes. Because of weather issues... because of moisture issues. Other times it is just not obvious....
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rainbowgardener
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