We are always trying to protect our plants from a late spring frost or extend the season in the fall by protecting from a early frost. The best way I have found is to cover them with a lightweight cloth call row cover. This spun cloth comes in different weights. Of course the heavier the weight the better the frost protection. The trade off is the heavier the cloth the less light it will let through if you have to leave it on for several days. I usually split the difference and go for a medium weight cloth. Keeping the cloth in place is a challenge sometimes because the colder nights are often preceded by a windy day as the front moves in.