On Fri, 19 Nov 2004 06:52:55 +0000 (UTC), "Franz Heymann"
wrote:


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?

Franz

It's not to stop transmission of UV, just to prevent UV from degrading
the plastic. You've seen what happens to non UVI polythene left in the
sun - it degrades to the point that you can crumble it in your hands.
The plastic made for tunnels has a life of several years (in the UK)
depending on quality, wind exposure and on being installed tightly so
it doesn't flap around and destroy itself.

=================================================

Rod

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http://website.lineone.net/~rodcraddock/index.html