new greenhouse experiment

I am going to try to raise vegetables in the greenhouse during the depths of winter. While the greenhouse has been used to growing seedlings in the spring and prolong the harvest in the late fall, it is much more difficult to raise veggies in Jan - more so if you don't want to spend a fortune on energy bills for lettuce. I can get seedlings started pretty easily (and cheaply) by using low watt heating pads - two 9x20" 17W pads will keep an insulated plastic tub at about 70C. I used plastic seedling trays inside the tub and water them from the bottom by filling the tub with water. But then how to raise the seedlings into veggies?

 The problem is to keep both the air and soil temps above freezing, cheaply. My solution was to fill the spaces in my cinder block thermal mass with dirt. Of course, I first put several layers of non-degradable plastic mesh below the top course of bricks to keep the dirt in. Without any heating, the soil temp measured 50C in the mornings during the several day cold spell we had. The greenhouse itself does a very nice job of heating up during cold but sunny days and retaining that heat well into the night. However, a prolonged overcast cold spell will result in sub-freezing temps at night. I do have a 1500W heater in the greenhouse, but that is not what I call a cheap route. I then decided to put up another thermal barrier around the plants on top of my thermal mass. This isn't much, just a thin plastic sheet, but it keeps the convection currents away.

Then, besides the grow lights I put in, I got two cheap 250W chicken heater lights. The grow lights and the heat lamp are both on timers working out-of-phase. And they aren't really grow lights since those are exorbitant. A little research shows that the "cool-light" bulbs are not that far off in wavelength from the grow lights, and way cheaper. Got the bottom tier fluorescent fixtures from Home Depot and we're on our way. I will probably have to transplant the first of my seedlings next week. High on Tues is predicted to be 18 so it will be a good test right off the bat.

The good news in all this is that it was way cheap (if it fails). I had all the blocks, dirt, plastic, and even some of the bulbs. Ended up just needing PVC for the frame, the light fixtures (that I can always use elsewhere), and the heat lamps ($7 each). So a fun test to try.