Some of us here are already aware of this trick . . . but I'll share it anyway - just in case somebody's here that doesn't know it.
Save your plastic fruit bottles - get an exacto knife and slit them in half.
Then when you have planted something and you're not sure if the temps might drop, just place your top over the
plant or
seeds.
Leave the cap off, of course, so the
plant can breathe.
Put stones around it to hold it in place or put a stick down it.
Don't discard the bottom part of the container - they come in handy for collecting pine cones, stones and little twigs you might want to save for fill.
Waste not - want not!