Patio Greenhouse

This year, for the first time, I will be attempting to grow seeds for annual flowers and vines. I pretty much have the growing area set up. I have a seed heating mat and I put in shop lights that I can lower and raise as needed. Now I'm wondering about hardening off seedlings and whether or not one of those small, cheapo patio greenhouses would add any benefits to this process.

I live in zone 4b and would like to know how soon or at what temperature seedlings could be placed in a patio greenhouse? Should the greenhouse be placed somewhere in the sun or should it get more shade? At what temperatures would I need to worry about plants becoming overheated in the greenhouse and when steps should be taken to ventilate?

Are there any other practicel uses for a patio greenhouse during the growing season other than using it as a plant stand?

Any and all comments, suggestions or advice would be welcome.

You have to be very careful about regulating temps in such an enclosure. The smaller the "greenhouse" the faster it will heat up and cool off. Any gains in temperature could be offset by loss of temperature regulation. You could get a crispy crop in very little time. SB

Most any seedling would benefit from being in the full sun while they are growing. It stops them from getting leggy, and the sun speeds up the growth process. My seedlings are in the greenhouse from start to finish (i.e. I transplant them in there and keep them there until no danger of frost hitting them outside) I would think it would be ok to put them in the greenhouse once the sun warms the gh up to 60 degrees, but you want to ventilate pretty soon after-my thermostat for the fan is set at 80 degrees, and on a sunny day (no matter what the temp outside is) the fan comes on about 9 or so am. A greenhouse heats up fast in the sun. Some annuals are cooler weather and can handle cooler temps better while younger, and vice versa for warmer annuals (vinca etc) How do you plan to ventilate? I would definitely bring them in once the sun goes down and it starts to get colder at night-late afternoon.
It seems like a lot of work to do everyday for the next two months? If your grow lights can keep the seedlings from getting leggy (stretching) then I would keep them in there for the next 4-6 wks, and maybe think about hardening off then.

I would add that legginess (internodal stretch) is controlled by several factors and another is the temperature swing between day and night, known as the "DIF" (ie, difference between day and night temps). Any reduction in legginess from increased sun exposure could be negated be extreme temp swings you might have in a patio greenhouse if you aren't very attentive to the ventilation. http://www.for.gov.bc.ca/nursery/fnabc/Proceedings/TempAndIntegratedControl.htm

I tend to agree with tigerlily, it may be more trouble than it is worth. SB

stressbaby, I thought about the DIF, but didn't want to overload him lol. Actually, wind can cut down on stretching, so maybe a fan on the seedlings would help. I know people in articles that have done experiments just brushing their hands across the tops of the plants on a daily basis to reduce heighth growth and there are machines that some gh's use. I was half joking about a fan, but it would be an interesting experiment in beaker's situation.
Beaker, I would also add that once you get the seeds germinated, you dont have to keep the soil temp up with a mat. The grow lights should produce enough heat. And definitely back off the moisture levels. The drier the soil, the better the roots develop.

I live in Northeast Ohio, in zone 5. I have been using patio greenhouses for several years to harden off my plants. I put the greenhouses on my patio which faces the south on one side, and the east on the other side of the patio. I use an electric heater to maintain the temperature in the greenhouses. They go up April 1st. The only problem is you have to be out there checking the temperature once the sun gets warmer aroun the 3rd week in April. From then on, you are opening and closing it.