How much will a cheap greenhouse raise temps?

[Chucknbob]

So I ran across a 4'x7' soft sided greenhouse today for $59. It's the type with soft clear plastic sides that roll up and down. How much will these raise temperature and how would I use it to extend my season?

I'm in zone 6 And usually just garden in several 4'x8' raised beds. I start seedlings indoors under lights and move them out from late march (lettuce) to early may (peppers, tomatos, etc).

[Michael W. Smith]

Greenhouses are amazing at heating up when the sun is out. Even on a somewhat cloudy day, they can warm up pretty good.

However, they have no insulating value, so once it's dark, the cold seeps in. Using some kind of heating source will help in the evenings so your plants don't freeze.

[Forcast]

so does that mean you cant start using one until the day/evening temps are above freezing? I would think even with a heater it would be hard to keep them warm?

[Callieslamb]

You can use them, that's what hoop houses are all about. As small as this one is, cover it at night or when the temps drop. Or cover the plants inside. I kept even heat-loving tomatoes alive on a shelf in an unheated garage in zone 6 by using a 40 watt bulb. I used a sheet of styrofoam insulation on the back side and bubble wrap on the front and sides. Opened it up during the day. When I had 8 shelves going, I used 2 light bulbs on different shelves. Worked great.

[1shotwade]

I would thing you could use black plastic bags inside to absorb the suns heat and I am thinking if you had a medium to hold that heat for a while,( like they use rocks in the fire to warm your sleeping bag)you could keep the plants warm at night. I do know that salt is one what they use to transfer heat from solar collectors to the storage facility. Maybe salt inside a black plastic bag would work.
Just a thought.

Wade

[TnAndy]

Sun out, it will be easy to overheat and cook things. For example, today our hoophouse was reading 85 degrees inside with outside temps in the low 30's. Unless you have automatic ventilation, you'll need to watch it as winter wanes and the sun gets stronger.

At night, with a double layer of plastic with air blower, and no heat, the inside will stay about 10 degrees warmer than outside. If night temps are forecast dipping to mid 20's, we do nothing. 20 or so, we put frost blankets on the plants inside. Mid teens or lower, I build a fire in the wood stove. Single digits, I add some propane heat. (not often....but this week, for example, low Sunday calls for 5 degrees, and a couple of single digit nights this coming week.