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Old March 14, 2017   #6
bower
Tomatovillian™
 
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Join Date: Feb 2012
Location: Newfoundland, Canada
Posts: 6,793
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+1. Coming from a cold place I can tell you that cukes, squash and beans are among the most sensitive to cold - even more than tomatoes.
That being said, I tried early squash in my (attached, unheated) greenhouse one year, started them same time as tomatoes. We certainly had some cool nights and days, that dropped below 50 F and not below 45 irrc, and the young squash plants weren't damaged. It was not actually freezing inside and that was ok for them, because the sheltered greenhouse keeps off moisture and protects from windchill that can easily injure them outside.

If I had to protect them for one night only, it could be worthwhile to bring them into the heated indoors just to be sure. But if there's a day or two of cold, they'd be better off in the sunroom for the light that they need, as long as it's closer to 50 than 40. You can cover them with row cover or a blanket at night, then take it off in the morning when the sun's warming starts to kick in..

Another trick that can make the difference in unheated sunroom or greenhouse space, is to raise them off the ground, especially if you can sit them on top of closed buckets of water or anything a bit massive - on top of empty planters full of soil is also good IME. The coldest place at night will be on the floor/the ground because cold air sinks, warm air rises.

I have sometimes filled juice bottles with hot water and put them under or around containers on an especially cold night. Two liter bottles lost all their heat by midnight (were cool to touch) but still they moderated the temperature enough to keep my plants damage-free. Bigger bottles or buckets will lose their heat more slowly. Clear plastic bottles will also pick up heat from the sun the next day, so you don't have to refill or use more hot water.

Last, one of the best things I tried for to capture solar heat early in the season was some black cloth grocery bags full of small to medium sized rocks. The sun's heat penetrated really well and warmed the rocks, and they give off their heat more slowly than water. The 'shapeless' mass of rocks in a bag could be arranged easily as I wanted, exposed to the sunshine and heaped against the containers to keep soil warm during the night.
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