Re: Tree dahlia (D. imperialis) question....

At 09:55 PM 1/14/99 EST, you wrote:
>
>I'd like to learn more about planting/growing this interesting species in my
>climate.  Anybody out there care to offer firsthand experiences with it?  I'm
>in Contra Costa Co., California, about 30 miles east/inland from San
>Francisco.  I know this plant does really well *over the hills* in Berkeley,
>etc., but how 'bout out here where it can get to 95+ degrees in the summer?
>and some frost in the winter?  Anybody have similar growing conditions?  Any
>advice would be very much appreciated!
>
>Best to all, C. Carter

C. - 

As with most Dahlias, this plant can grow easily in your slightly cooler
climate - the problem is really one of timing.  Even over here (I'm in
Oakland), where this plant is fairly common and seems to grow without
any care, its late flowering can be a problem.  I've often been heard to
tell clients who ask "When does it flower?", this rather cynical bit:
You can tell that the winter rains are coming along when you see this
Dahlia put forth its large, branched, flowering scapes, and just about
when the first flowers open, our first winter storms arrives to rip them
off the plant and distribute them throughout the neighborhood.  Obviously,
providing a sheltered spot for this late flowering is a very good idea,
providing you with much more chance of a good show.  Some overhead
protection can also help, though providing enough height for the 10-12ft
stems can be a challenge!

I grew this plant in an open, exposed spot for years (in the south Bay
Area, where it can get hotter in summer than here), cutting it down to
the ground each winter, which produced impressively huge stems and tropical
looking, tri-pinnate leaves 4ft long and 3ft across!.  Since the plant
was cut to shreds by winds and rains just before it would have flowered,
I seldom was able to enjoy this event.  But it still was a wonderful
specimen in that garden!  In milder climates, the stems can live over
and even sport evergreen foliage throughout the year, but this doesn't
necessarily help it to flower well either, sometimes producing smaller
and fewer flowers hidden among the leaves.  If you can leave some part
of the plant above ground each winter, then a good hard pruning will
help to inspire strong new shoots, better foliage and flowering.

I have seen the white flowered form, which is quite nice (they type
species is a rosy-purple).  I like the large, single, eight-petaled
flower, which hangs sort-of downwards facing (handy since they are borne
so high up off the ground!) - much more charming than most Dahlias to
my mind.  There are double forms of both the white and the purple, but
many people (myself included) do not find them as attractive.  The form
of the flower is more 'typically' Dahlia, and they have the obnoxious
habit of holding onto the spent flowers which hang like crumpled up
brown paper among the new, opening flowers!  Kinda spoils the whole
picture!

So, go ahead and give it a try in your more extreme climate.  Help it
find some deep water by heavy mulching and deep irrigation to get
through the summer months, and try and keep it out of prevailing
autumn rains and cold winter winds.  Even without the flowers, it is
well worth the space if you like the impressive!

Sean A. O'Hara                       sean.ohara@poboxes.com
h o r t u l u s   a p t u s          710 Jean Street
'a garden suited to its purpose'     Oakland, CA 94610-1459, U.S.A.
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