I cut off the bottom of my clear *Juicy Juice* containers, and plant
things like cucumbers
*who really like to be directly planted into
the ground and not distrubed by transplanting..*
directly in to the garden last year...
and let the container's act as mini~greenhouse
And we had several cold days/nights and I kept the caps of the juice containers and covered them during the night and off during the day hours *it would cook the heck out of the seedling
just emerging if the sun comes in and builds up too much heat..
I think also you get the hang of it, on how to put the cap on or leave in heat once you've done it enough *or had accidents' that you learn from* and see how it goes..
I do the same for the greenhouse
, learning the first year was really alot of man hours in it,
with thermometer's in it and checking temps, sun/clouds vs cold winds, etc.. and opening and closing the door as needed to either let hot air out or keep hot air in going into the night hours or clouds...