Q. Is it neccessary to use lights in your plastic covered greenhouse that you start your plants in. Also what do you use to heat it?
A. Lighting from the sun has always been adequate in our greenhouses. However, you must be certain that you build the greenhouse in full-direct sun.
Heating is another matter. In cold climates you may need supplemental heat – especially to get the plants started. The least expensive way to do this is probably to do a “greenhouse-within-a-greenhouse”.
In one corner of your greenhouse put up a layer of plastic on the inside of the greenhouse frame between the door and the corner, and along the side wall – between 4 and 6′. Do the same for the roof in the same area. Then finish by attaching plastic to hang down from the rafters until you have completely enclosed the chosen area.
Put an electric space-heater on the ground in this small area, and do your seed germination in that warm area. This is much less costly than trying to heat the entire greenhouse.
You must plan your timing, so that when the seedlings are transplanted into flats too numerous to fit in the smaller space, the temperature in the larger greenhouse will be conducive to growth without expensive heating bills. The larger greenhouse should get into the high 50’s and low 60’s during the day, and not freeze at night, in order for seedlings to be okay.