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Re: grevilleas - Light intensities

On Tue, 10 Feb 1998 Tim wrote:

>The chap I know who's growing various forms of G. australis in his
>garden in the UK - on the Wirral (3-4 miles from the sea; a little
>further from Ness Botanic Gardens; so probably a degree or two colder
>and a touch wetter than here, on average) - has tried G. x gaudichaudi
>and G. aquifolium in the past but both got caught by a sharp 80s
>winter early in their lives and didn't survive. Being a VERY
>controlled pessimist, he hasn't tried again.

If you are talking about the spectacularly cold, 'once in 300 years'
winter of 81/82, I wouldn't be at all  surprised to hear of losses -
especially near Ness, which was as badly hit as most places.  However,
to limit oneself only to those plants which survive such winters is
rather narrow minded don't you think?   Even 'ancient' specimens of
Grevillea sulphurea  & rosmarinifolia were cut back to their
rootstocks or killed outright during that winter ( I lost several
thousand roses in pots at the time), but it didn't stop most of us
scurrying to replace them as soon as possible.

>David makes a good point about light intensity, too. So Michael's
>information about G. x gaudichaudi liking filtered shade in California
>would probably need to be translated into 'must have full sun' in a
>low light and heat area like this: yes? 

Absolutely.  As one moves further from the equator, light has to
travel a greater distance before it hits the earth.  This, combined
with the diffusing effects of a proportionally greater thickness of
atmosphere and a broader 'spread' at any one point, effectively
reduces its intensity.  If we look at the latitudes - Tarifa, is the
most southerly point on mainland Spain (36'1"N) whilst possibly the
northernmost (coastal) mediterranean point is Monfalcone close to the
Italian/ Slovenia border (45'49"N).  Compare these with Los Angeles
(33'45"N) and then look at what we have to offer.  Where I live in
Torquay, we are 50'28"N and your area is approximately 55'N. !!!  I
don't have relevant data to hand, but would guess that light intensity
in the UK is approximately 20 - 30%  less than that of southern
California .  As a result, plants defined as requiring 'light shade'
there, would almost certainly require full sun over here.    

One factor often overlooked, which goes someway towards redressing the
balance, is that during summer, our days are somewhat longer than
those in more southerly climes.  This enables plants to make very good
headway once growing conditions allow, since we often get as much as
16 hours or more of daylight during the peak growing months.  This
compares with around 12 hours further south.   However, these 'long
days' have the effect of producing softer, lusher growth, which if not
'ripened' by long, dry sunny periods during early late summer/early
autumn, is likely to be frost sensitive.

For this reason, many gardens in the east - East Anglia-
Cambridgeshire (in part)/Suffolk/Essex - UK, are remarkably successful
with many medit plants.  There, low humidity, very low rainfall and
above average sunshine help create conditions which such plants enjoy,
despite the fact that frosts can be severe.   Last summer, it was
announced with much amusement and a certain amount of disbelief, that
parts of East Anglia were 'drier' than the Sahara desert.   I dare say
that the desertification of Britain came to an abrupt halt with the
advent of the winter storms.

David Poole
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