Hello, I am new here and have plans to give gardening another try. I was wanting to start some seeds but I don't have room to keep them in the house. My kids did get me a small green house for my birthday last year and I'm wondering if I can use that. I have a nice sunny spot that gets sun pretty much all day ( when it isn't raining). Will I be able to start the seeds in a green house? I won't have a heat source other than the sun. Can that work?

By the way I am in southeastern TN zone 7.

It depends on what you want to start: many annuals like Zinnias, Love-lies-bleeding or ornamental Sunflowers can be sown directly in place after the weather has warmed up in the Spring.
But if you want to start, say, eggplants you will need a warm place in the house or a heated tray. Some seeds (strawberries for example) require stratification for sprouting, meaning being stored at below freezing temperature for a time before being sown. Others yet (some peonies) require scarification... it all depends on what you want to grow.

If you're talking about one of those portable ones, about 3 or 4ft wide, they're not really made for seed starting. I'm in Oklahoma and my biggest issue is they get too hot. It can be below freezing & the inside will get up to 70 on a sunny day, so on our random 50 or 60* days seedlings will fry. They also don't retain heat so they won't keep anything protected overnight.

I agree that it's very hard (nearly impossible) to regulate the heat in a small greenhouse for seed starting.

Again, depending on what you want to grow, and how much of it, you don't necessarily need much room at all to start some seeds indoors. Even a small (2-foot) fluorescent or LED light fixture would probably let you do a whole flat, and a 4-foot fixture (inexpensive shop light) would let you do 2 flats. Really just a matter of rigging something up to suspend the light from so that it can be positioned just a few inches above the plants. (For initially sprouting the seeds you can just put the flat - or whatever you are using to hold the packs or pots - in a nice warm spot, then move it under the light once your seeds are sprouting.) Alternatively, you might want to consider winter sowing - here are links to a couple of articles on this site that will give you an idea of how to proceed with that:

https://garden.org/ideas/view/...
https://garden.org/ideas/view/...

I hope you're able to give it a try - starting from seed is very rewarding!