A bargain in a cold frame starts with that clear plastic storage box that cracked or lost its lid. Try to recycle them, and you have a big job breaking the plastic up for the bin. I don’t know about your city, but in mine, if it’s not in the recycle bin, they aren’t taking it.
This spring, I had dual problems: not enough greenhouse and cold frame space, and about four of the storage boxes at the end of their useful life.
Moving things around one evening, I dropped the boxes in the garden when called in for dinner. The following day I saw the humidity inside the boxes, and one plus one equaled a mini-greenhouse or cold frame.
The photo shows several of them protecting a row of sugar snap peas and some cauliflower. If it’s going to get windy, I can place a brick on the top.
In a few weeks, I won’t need them for the season. Instead, I’ll store them for the fall growing season when I put in late spinach and lettuce.
You maybe have been using this idea for a couple of years already, but it was new to me and perhaps will be new to some of you.