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Re: grevillias, drainage, clay

Rachel asked:

"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."

Clay soils are not uncommon in mediterranean climates. In particula,r with
respect to Grevilleas I can quote from Olde and Marriottt Vol. 1. They say;

"Most grevilleas grow naturally in soil with a high proprtion of loam or
clay. Few grow in deep sand, and even in heathlands and shrublands where
many occur the soil is commonly shallow sand over gravelly loam or clay.
Likewise, few species can be cultivated successfully in deep sandy soil,
unless it is given better structure and water-holding capacity."

In California my experience with Grevilleas would echo theirs. I could not
say it better. Clay soil is not necessarily badly drained but it does hold
on to moisture and has a high moisture retention that makes it easier for
these plants to withstand long droughts. I have seen grevilleas flooded
coimpletely and grow rapidly after the water drained. Check with UC Santa
Cruz. Many parts of Australia have such condtions. In fact, I have found it
necessary to add some clay in order to make the soil more easily wettable
after a drought.
Good luck!

Andrew
San Diego, California
awilson@fda.net
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