"Andy wrote in message

That's no real issue and can easily be removed. I quite like to see
a certain amount of lichens on roof tiles. It makes them look more
interesting.....


Apparently lichens only grow in places of low atmospheric pollution,
so it's a good indicator of air quality, as well as any aesthetic
benefit.

but is the same true about moss? In fact, are moss and lichen
synonymous?
I know that lichens are rarer than they once were.

Actually, since the Clean Air Act came into force (yes I remember that!) the
pollution has reduced drastically. Most came from coal fires and those of us
of a certain age will remember those horrid yellow filthy smogs every winter
in the good old days. Whilst most pollution still comes from the home,
central heating etc, vehicle pollution has made drastic reductions too in
recent years, in fact the pollution from cars is a reversing trend despite
more and more on the roads. Because of this Litchens can now be seen on many
rooftops, walls and trees, even in towns, which is something one never saw
when I was a kid. Take a look as you drive along, you will spot some roofs
covered with grey litchens.

I seem to remember Kew saying recently that they were on the acendancy in
their garden and you aren't too far from there.


There are a whole spectrum of lichens and some will grow in moderately
polluted conditions. Others are more sensitive to conditions, so for
example you will see a richer set of lichens in a forest in Wales than
you will in town.

Mosses are rather different, in that theyare plants and produce
chlorophyll themselves and are generally attracted to places where
there is moisture - hence finding them in gutters...

Clearly it makes sense to remove moss from gutters to avoid them
cloggin and water running down the walls, but there is no reason to
remove them or lichens from roofs. Arguably there is more risk of
damage from blasting with a pressure washer or from use of chemicals.

True, it's a bit like Ivy, you do the damage getting it off.

Whilst there are some "green" roofs in the UK (Notcutts GC in Staines for
one) it is a strongly growing trend on the continent the idea being that
building a house and then having a green roof does not reduce the green
habitat for parts of the animal kingdom one bit. It's a bit like building
underground especially for the flying insects/birds.
So whilst moss in your gutters is not good, on the roof it isn't a problem.

Incidentally in certain parts of the country people used to plant Houseleeks
( Semperivivum tectorum ?) on their roofs to ward against Witches and
lightening. Plant them on the sunny side of the house. :-)

--
Regards
Bob

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