Update on growing lettuce all winter!

20 years ago

Last fall we put up an attached 8x12 glass greenhouse and I posted here about wanting to grow lettuce all winter in an unheated greenhouse. Since the temps go down in the teens quite frequently here, and we get very few days of sunshine, I had to find a way to keep the plants from freezing. Bubble wrap gave us about a 5 to 7 degree difference from outside but that wasn't enough. There is only room for two large garbage cans full of water, but that helps to keep the temperature just above freezing. I put row covers on at night to give me another 5 degrees above the outside temps. I even tried putting hunks of soapstone on our woodstove during the day and tucking them in among the plants at night to release heat slowly during the night. But that only lasts a few hours.

A couple weeks ago, my husband suggested putting our extra gutter cable into the raised bed. I zig-zagged the cable across the bed on top of the soil. What a difference this has made! The temp just above the bed hasn't dropped below 40 since. The lettuce plants had really slowed down with the low light, but now the combination of lengthening days and the warmed soil has worked wonders. The plants are perking up and showing some growth again. On a really cold night, I still put on the row covers to hold in the heat. Right now it's 25 outside and 50 in the raised bed.

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Comments (9)

User
20 years ago
Good for you, MJ.

Your results with gutter cables are interesting. On the citrus forum some time back, gutter cables were discussed as a method of warming containers, but this idea was dismissed with the belief that they would not be powerful enough. In the case of the citrus, the goal was to get the containers to 60-64*F, and that perhaps is the difference.

What is the temp differential between the surface soil and the ambient air elsewhere in the greenhouse? SB
salads_r_us
Original Author
20 years ago
Hi, Stressbaby. There are two wire shelves above the raised beds. The temp on the highest shelf -- about 3 1/2 feet above the bed -- is usually a few degrees higher than the bed, so the heat must be rising from the cables. I can hold this in when it gets cold by using row covers. On the house side (north) of the greenhouse the temp runs about the same as the raised bed. That's because there's a blocked-off heat run coming in at floor level that leaks some heat and the two garbage cans of water sit right in front of it. The gutter cables run through the beds on the south and west sides of the greenhouse.

I'm not sure you could get up to 60-64 for citrus plants if the outside temps were really cold. This is perfect for me because I have all cool season plants - lettuce, herbs, and sweet peas.

I wish I could post some pictures here, but I can't find the info on how to do it.

MJ
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billtex
20 years ago
Excuse my ignorance, but , what are gutter cables and where do you get them ? bill tks.
salads_r_us
Original Author
20 years ago
Gutter cables are probably only sold in the northern part of the country, Bill. They're meant to be zig-zagged along the lower edge of a roof and they emit just enough heat to keep icicles from forming. We happened to have an extra set of them not being used. I don't know how they compare in price to regular greenhouse heating cables.

MJ
mawkhawk
20 years ago
Bill, you can order them from the web at various sites. Here is one:

http://www.improvementscatalog.com/home/improvements/536867378-Roof-Heat-Cable.html
froggy
20 years ago
lol, how much is ur electric bill?

ur paying after all ur expenses of work and e' and etc. about 75$/lb for ur lettuce

froggy
weebus
20 years ago
Guess what Froggy. Homegrown lettuce, the satisfaction of growing it yourself, the flavor, freshness, and the peace of mind you get knowing that pesticides weren't used on something I ingest is worth far more than a dollar or two.

It boggles my mind that 90% of this board equates everything to he all mighty dollar. That's the reason I rarely post anymore.
salads_r_us
Original Author
20 years ago
We have to run gutter cable every winter, froggy. We have always had three cables on the house and they've never made any appreciable difference in our electric bill. We didn't have to buy the gutter cable we're using in the greenhouse because we changed a part of the roof pitch and didn't need that gutter cable anymore. It's probably cheaper to use the greenhouse heating cable if you have to buy it in the first place, though. We eat a lot of salads, so we were going through 4 or 5 of those 2.99 bags of baby lettuce a week. The way I look at it, we're coming out ahead of the game, and the lettuce is delicious. The work doesn't factor in at all, because I love being in the greenhouse when it's windy and snowing outside. On sunny days, we turn off the gutter cables and blow the greenhouse heat into the house.
MJ
User
20 years ago
Amen, Weebus!

Hey Froggy, it's a hobby. If ur (sic) not a professional grower, then maybe ur (sic) willing to spend the time and money on it. At least this way you won't be spending money on Effexor and Zoloft.

Speaking of the almighty dollar, have you read the new Privacy Policy and Terms of Service? It allows iVillage to sell any of the content here, including your e-mail account. Kind of scary.

As for me, I'll be over talking to Dave...SB