To start my seedlings off to a good start, I tried several different kinds of greenhouses (being my first time in growing anything). I found that the self watering ones with the grow pellets worked the best for me.
The growing pellets expanded into just enough medium to fill the cells.
This greenhouse self waters for 10 days before you have to refill it with water. You first soak the mat in warm water, then pour the recommended amount of warm water over the pellets and watch them grow. The cover with the plastic sheet it provides.
The next self watering greenhouse I purchased was one with more smaller cells.
I planted my lettuces and bok choy in this one. They've been growing by the window with only sunlight...from the start (as they need light to germinate). This greenhouse came with a plastic dome...unlike the large cell one above that came with just a small plastic sheet cover to retain moisture. Both worked great.
This is what it looked like after the pellets expanded & smoothed out. They're very easy to set up...just pour warm water over them...the instructions tell you how many cups depending on the size of green house you get. This one self waters for 10 days before you need to fill up the bottom with water. I used a disposable chopstick for my seed poker, and an old tweezers to pick up tiny seeds and place them.
I purchased this larger 72 cell greenhouse to plant my marigolds...I learned from the first few that it's a good idea to plant similar plants within one greenhouse due to the different germinating time (and needing to put them in light at that time), and differing temp requirements as well.
The 72 cell greenhouse had 2 trays in it. I filled up one to show a before and after. Water placed in the left tray here...they swell up like towers...then you need to flatten them gently before planting the seeds.
The first greenhouse I got was this 72 tray heated one. Unfortunately for me the heated mat that came with it was not functioning...and i realized this 4 days later. But Lowe's was good about replacing it when I went to return it. I used a basic potting mix, that I wasn't too thrilled with. However I think the lack of success I had with these was the watering...it was either not enough or too much...they either didn't sprout, did and got a little too much mold for me to keep, or just took their time. So I'll never get a non-self watering one (that's my personal preference). This pic taken before planting. I should have moistened the mix before planting.
It came with a plastic dome to keep in the moisture.
The last greenhouse I got was one that formed its own pots and was also self-watering. I used this one to grow some herbs and my cucumber.
I purchased it because I purchased extra pellets like this that form their own pot...but didn't have a container for them.