"derryl" wrote in message
...

Polythene is seriously degraded by UV rays. The UV inhinitiors
extend
the life of your polythene. And you will get a longer life out of
thr
polythene.

It has nothing to do with plants at all.



On Fri, 19 Nov 2004 18:22:58 +0000, Alan Gould
wrote:

In article , Franz Heymann
writes
Why do polythene tunnel covers need to block UV radiation?
Surely the same plants, growing in the open thrive the full dose
of UV
radiation?

I think you may have a point there. I suggest that you advise the
suppliers of poly-tunnel covers that they have it all wrong and
tell
them what material they should be marketing.

I do indeed have a point which you clearly have not appreciated. The
desirable polythene is *not*used because it blocks UV, as you
originally implied. All polythene always block UV light. The
desirability of the UVI/EVA polythenes lies in the fact that they are
reasonably protected against UV damage to themselves, as numerous
posters have now pointed out.

Franz