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Re: grevillias, drainage, clay

At 03:39 PM 2/10/98 PST, Rachel@haasjr.org wrote:
>A propos the discussion about grevillias--I was under the impression 
>that the heavy clay soil in the Bay Area was somewhat of a problem in 
>growing grevillias here.  And--while I'm making my first, very humble 
>posting on the list-serve--could anyone comment on the relationship 
>of heavy clay soil and mediterranean climates...In reviewing and 
>selecting mediterranean cultivars, it seems that the vast majority 
>require good drainage.  Are there other mediterranean-esque places like
Northern 
>California that have wet, temparate winters, dry summers and heavy 
>clay?

Actually, where most of us Californians live are the floodplains (which
used to be some of the richest agricultural regions of the world),
hence the clay soils.  Some residents live on other types of soils
(Alameda and San Francisco, close to me, tend to be sand based soils)
which have different types of advantages/challenges.

Many of the desirable California natives (Ceanothus, Arctostaphylos,
etc.) are native to hillsides, coastal cliffs, and other well-drained
soils, so they don't really enjoy the heavy clay sections either.  It
is a common misconception that since it's 'native', it could grow almost
anywhere in California.  Since our state is one of the most diverse
ecosystems in the world, there are no end to the micro-climates and
divergent soil profiles.  Much of the state is Mediterranean in
character, but each locale has its own 'expression' of this climate.

The Mediterranean basin is characterised by steep cliffs and almost no
'soil' as many of us know it.  Plants from this region, as well as species
from South Africa, Australia, Chile, and our own state often do require very
good drainage, but not all.  Some species are also more adaptable than
others.

Grevilleas are a good case in point, growing best on sloping ground if
the soil is heavy, or in generously amended berms or mounds where plenty
of gritty mixture is used.  Or if you happen to have a mountain garden
(a friend's garden at the base of Mt. Tamalpias springs to mind), you can
grow these plants easily without soil work.  My own garden is very steeply
sloping, which helps mitigate the black clay soil's drainage problems, but
I still must amend, amend, amend to have many plant thrive, while others
seem little concerned and grow abundantly!

 
 Sean A. O'Hara                     sean.ohara@ucop.edu
 710 Jean Street                    (510) 987-0577
 Oakland, California 94610-1459     h o r t u l u s   a p t u s
 U.S.A.                             'a garden suited to its purpose'
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