This system of frost controls work both in the spring for late frosts and in the fall for early frosts.
Frost control trick – you want this because frosts are a royal pain in the anatomy for gardeners and can wreak havoc on both the garden plants and the gardener’s morale.
Here’s what I used to do in the nursery.
Last thing at night on cold nights, I’d go out and mist all the plants – put as fine a spray on top of them as possible but thoroughly soak them all down. By the time I’d finished, everything (including me) was thoroughly soaked through and wet everywhere.
First thing in the morning (and I do mean first thing) before the sun had hit the plants, I’d repeat the soaking. Sometimes there was frost on the plants -that’s OK.
That frost had given off heat in forming (remember to get colder, a material must lose heat) and protected the tender leaves.
When I put more water on that wasn’t freezing, it too added “heat” and melted off the frost leaving green leaves behind.
This technique works on many plants *if* they’ve been hardened off and the frost isn’t a heavy one.
Nothing is going to stop 5 degrees of frost but if it’s only 1 degree, then this technique works.
For *really* cold nights, it is far better to cover plants with a wet sheet or other wet insulating material (not plastic).
More heat will be stored by a wet blanket (water holds heat)than a dry one. And this means it takes more cold to freeze the water and get under the blanket to the plants.
(I note this was a problem with the nursery when we had over 25,000 plants outside)