"P" emailed to ask, "Do you use the coolers in the greenhouse, or only outdoors?" So far I'm only using them in the mini greenhouses, but there's no reason that they can't be used outdoors. In fact, one blog follower is a big user of coolers for her outdoor gardens. They are old picnic coolers, both the styrofoam ones and the hard plastic ones. The insulated sides help protect the plant roots from getting too hot. Plus it helps prevent the soil from drying out over rapidly.
I'm a collector of old coolers. The trash dump thrift store keeps an eye out for them, but I've discovered that I have competition for them. Guess somebody around here got the same idea or read my blog about it. But I do manage to snag a few more each month. They can be broken, worn out, missing lids, I don't care. Punch a few drainage holes in the bottom, fill them with potting soil mix, and they are ready to go.
I use them to grow "eaten raw" veggies in the mini greenhouses. Lettuces. Kale. Asian greens. Any other thing used for mixed salads. I'm also growing carrots in them because my garden soil is too stony for them.
I don't have nearly enough yet for my needs. So I also use sturdy cardboard boxes that I line with a heavy duty trash bag. The black box in the middle (photo above) is a cardboard box that bananas were shipped in. So far I have 11 old coolers in service.