I’ve been using floating row covers in the greenhouse lately to add an extra level of protection on cold nights. Jugs of water around what few tender plants remain in there help a lot, too. The water warms with the day’s heat, and at night, when temperatures drop, the heat radiates from the jugs and warms the plants. I have fresh salads daily, beets now and then, and a batch of collards for the family most weekends — all this using no supplemental heat.
Temperatures have dipped as low as 21 degrees Fahrenheight overnight outdoors, but under the cover in the center bed, the lowest reading has been 31 degrees F. That was enough to damage a few tomato plants, but the fruit survived well enough that my father-in-law had fried green tomatoes for lunch a few days after Thanksgiving. I picked the last of the green tomatoes and pulled the vines earlier this week to free up trellis space for the maturing snow pea vines. I’m not a big fan of green tomato cooking, but I did find a new recipe for green tomato jam that might change my mind. I’ll let you know after I make it this weekend.
About those covers – they’re made from spunbonded polypropylene and can last several seasons. My oldest covers are a light-grade from Reemay, and I lay those along the outer beds where I have mature beets growing. The beets can survive without the covers, but I think the few degrees of warmth the covers hold in will improve growth. This year I added a heavier cover from Agribon that’s rated for protection down to 26 degrees. I used it on the center bed over the tomatoes, and on that 21 degree night, the only damage the plants suffered was some freezing on the upper branches. Because the cover has to drape over the trellis, I needed a wider width, so I bought a cover that’s 15 feet by 50. That covers the trellis nicely, with plenty on each side for the spinach and lettuce beds next to the trellis.
The down side is maintenance. It takes a while to cover the plants, and uncovering them on warmer days is a messy job. The covers usually are wet from condensation, and the big cover for the center bed is awkward for one person to manage. With practice, I’ve cut the covering and uncovering time significantly — if you don’t count the time I take for snacking on the produce.