Re: tree dahlia?
- Subject: Re: tree dahlia?
- From: &* C* M* <j*@earthlink.net>
- Date: Mon, 12 Jan 2009 23:58:31 -0800
On Jan 12, 2009, at 6:27 PM, N Sterman wrote:
Janet, how big does a piece of rhizome need to be to be viable?
Will I be looking for "eyes" on the rhizome?
Nan,
As with other dahlias, Dahlia imperialis has tubers rather than
rhizomes (the latter are defined as underground creeping stems). The
eyes appear above the neck of the tuber, along the base of the old
stem. Thus, the clump of tubers must be divided with a vertical
section of the old stem attached. This is best achieved by digging
up the entire clump intact with the help of a spading fork, then
cutting the clump apart with an upward slice of a sharp knife through
the base of the stem. If the neck doesn't have a portion of the stem
included, it is very unlikely to be viable and will almost certainly
rot.
This species is a short-day bloomer. In the Hall garden in Pasadena
(Sunset zone 21), the 15-year-old lilac-pink c;one of the giant
dahlia usually begins blossoming in late October and often continues
through April unless cut down by frost. It is planted adjacent to
the tennis court and gets good heat radiation, so it keeps blooming
on top through all but the coldest winters. Each stem is tied up at
several levels to the 12-foot chain link fence, so it is supported
through most winds.
It flowers most profusely four or five feet above the top of the
fence. The clones in circulation all appear to be either sterile or
at least self-incompatible, so I have never seen any seed set.
Still, when the faded flower heads become too unsightly, I climb a
ladder to deadhead them. The lower leaves gradually dry up and look
unsightly, so I have to remove them periodically. Frost tends to
pool, but by the time cold weather comes most of the lower stems are
bare, and the blossoms are high enough to be above the frost unless
the weather dips into the low 20s F. I cut stems back just above a
node to about 2-3 feet tall when it stops flowering and there are no
longer any buds coming (late spring). I feed it monthly in summer
with a high potash fertilizer to encourage sturdy stems and good root
development--then lay off fertilizer after September. In hot weather
it gets watered deeply once week.
David, Janet, and others have pretty well covered the other aspects
of this plant. I wouldn't call it a mainstay of the garden--more of
a curiosity--but if one has enough room for it and time to keep it
groomed, it can be attractive and interesting.
John C. MacGregor
South Pasadena, CA 91030
USDA zone 9 Sunset zones 21/23
