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Re: [SG] What about hydrangeas? (Was: Cutting back perennieals)

Actually, Nancy, it depends on what species they are; that determines
whether they bloom on old or new wood.  If they bloom on old wood, that
means they set their flower buds in the summer for flowers the next year -
not necessarily in spring flowering, just the next season.  If they bloom
on new wood, that means you can whack them back in late winter or early
spring and they will grow new wood and set flower buds and flower.

Now, who does what?

Hydrangea macrophylla spp. (bigleaf Hydrangeas) all bloom on old wood.
These are the hortensias (mop heads) and lace caps that you mostly think of
when you think 'Hydrangea'...flowers in blue or shades of pink to purple
depending on variety and soil pH.

Hydrangea quercifolia - the Oak Leaf Hydrangea -  also blooms on old wood.

Hydrangea arborescens blooms on new wood.

(Both H. quercifolia and H. arborescens 'Annabelle' bloom at the same time
for me - summer)

Hydrangea paniculata also blooms on new wood.

So, in order to know when to prune, you have to know what species you've
got, or failing that kind of ID, you have to observe closely and see if
bigger, fatter buds appear along the stems in late summer and then see if
those buds make the flowers the next year.  If that's the case, you've
likely got one that blooms on old wood.

If you pruned hard in late winter/early spring and got bloom this year,
yours blooms on new wood.  If, however, you only pruned lightly and left
most of the stems, yours could be an old wood bloomer and you were lucky
enough to leave flower buds when you pruned.

As to the second flush of bloom....I simply dunno.  None of mine have ever
done this for me - wouldn't mind if they did :-)  Wonder if it has anything
to do with the fact that you're in a mild climate area?  Anybody else able
to speak to this point?  Not having bitter cold winters could make some
difference in how plants behave and I've no experience of really mild
winter temperatures.

Marge Talt, zone 7 Maryland
mtalt@clark.net
Editor:  Gardening in Shade
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----------
> From: Nancy Acton <madoka@YAHOO.COM>
> Date: Monday, October 05, 1998 2:44 PM
>
> ---"venies.place" <venies.place@MCI2000.COM> wrote:
> >
> > Should I cut my plants back before winter or leave them as is?
>
> I would like to know specifically when is the right time to prune
> hydrangeas. I've been told it depends on if they bloom in the fall or
> spring, and whether they bloom on old or new wood.
>
> Well, mine bloomed profusely in spring (I pruned in February this
> year) and are blooming AGAIN right now. And I can't tell whether the
> blooms are on old or new wood. I'm in zone 9.
>
> Would appreciate any suggestions,
>
> --nancy acton
> ==
> Nancy Acton  (madoka@yahoo.com)
> Northern CA, USDA Zone 9, Sunset Zone 16
>
>
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