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Old February 1, 2018   #108
bower
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Join Date: Feb 2012
Location: Newfoundland, Canada
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Nan, as far as I understand it, this only happens in certain circumstances, when cold air sinks and becomes trapped inside the high tunnel instead of flowing away. Specifically in still clear weather with little wind to circulate the air and disperse the cold air which naturally sinks, afaict.

This would not apply to row cover in any circumstances. In fact plants inside a high tunnel could be protected from this effect with a layer of row cover inside. In case of a low tunnel you could also throw row cover or a blanket over the outside to prevent the cold air from penetrating and becoming trapped in the structure. Row cover is permeable and yet it is better at retaining warmth than plastic.

It would be a mistake to assume that the "colder inside" condition is always the case. It may be more frequent or less in one high tunnel or another because of the lay of the land and the frequency of windless cold clear weather in that location.
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