Above Freezing?

In a relatively mild Winter, I can keep my greenhouse above freezing overnight with two 1500 watt space heaters. However, the last couple of nights we've had below zero temps in my corner of the PNW. I grow only lettuce and mesclun mix in my 15 X 20 greenhouse, and my experience is that those crops will take a freeze down to 20 degrees without too much damage. Still, I'd like to keep the temp inside the greenhouse above freezing if possible. Need some feedback here and ideas from other lettuce experts.

I am definitely not a lettuce expert, so h ope someone checks in that is an expert. It is/was 2 below zero here this morning. My little gh is on the NE corner of my garage. It is 10 x 14feet. I use it mostly to start seeds (soon must get them planted), and for holding potted plants for spring. I had to buy a new 120 heater last fall. My 25 year old 220 v. heater expired. The new one seems to be heating my small gh ok. I only want 50 or so degrees. I have small heat mats for seed starting. I will plant one small pot of lettuce seed this weekend, the pot will be set on the floor or maybe just on the slat bench, depending on the temp in the gh.

Tonasket, WA is in NCW about 25 miles south of the Canadian border in Okanogan valley.

Donna

If 32 degrees is your target, storing large amounts of water in the GH may work. The water will absorb heat during the day and radiate it back at night. And it takes 80 times more "cold" to freeze water than to lower it's temperature one degree, so the 32 degree target can be held a long time. Of course you might have to use a container that would not crack if the water froze completely. A flexible container or something flexible inside it could work.
Dave.

Rutholive, what kind of equipment do you use to start seeds in your greenhouse? I'd like to use mine to start my tomato, pepper and eggplant seeds but I'm afraid that it will be too cold in there. I have a small heater which will keep the greenhouse (an 8' square Rion) up to about 45 or 50 degrees at night, but I'm not sure how that will work for tomatoes and such. Usually I start them inside and then move them to the greenhouse once the true leaves are out. I start mine in Gardener's Supply styrofoam flats with wicking cloth so I don't have to worry about watering them so much, but I don't think they would work with a heat mat.

My favorite seed starting method is with Parks Bio-Dome. I've used the same dome for 3 or 4 years now, buying replacement sponges each year. I have the 40-cell and 60-cell sizes. For me they work very well. For warm temp. seeds I place them on a heat pad. Never tried lettuce in them, but don't see any reason it wouldn't work. It is amazing how fast the seedlings develop roots.

Donna

I used the Gardener's Supply flats for years, greenhouse_gal, and had good luck with them on gro mats. The styrofoam tends to even out temp swings, and the gro-mats kept the water that feeds the roots at a warm temp, which is transfered to the soil...and irradiated up around the edges. The water acts as a big "heat sink". Like the Park's Bio Dome, it's a closed system, so the temp/humidity remain relatively constant within the growing environment (assuming you keep the lid on). I switched to the Parks system simply because the "sponges" are much easier to transplant than the loose soil in the GS system. And when you get old, you go for the "easier" way...

right StonoRiver. I ordered a new supply of the sponges, but they haven't arrived yet, probably sitting in a truck at Snoqualmie pass waiting. There is so much snow and no path to where my other seed method trays, the grooved trays, that work very well, are stored that I can't even get to them. Very unusual for us to have this much snow.

Donna

I think I've used the "groved trays" (Root Starters?) too, rutholive, and had great luck with them also. Transplanting isn't as easy as the sponges, but they do form a nice compact set of roots that are longer than the Park Starts. I like to keep as much of the original soil as possible around the roots when transplanting, and sometimes when I "opened the book", I lost a lot of soil around the roots. Didn't seem to matter; the plants grew well anyway. I still use the Root Starters for all my woody's that I'm starting. Just wish the domes were taller to allow for some of the taller cuttings that I start...

I use potting soil that I sterilize in the oven. Then peat pots in domes till first seeds sprout. Uncover and keep moist but not soaked. When using peat pots you need to check often, as the dry fast. Oh,. grow lights placed an inch above then move to South window when first real leaves appear. move to GH latter.