In Maryland Zone 7 we get the four full seasons of temperatures. We often get a period of great weather in February or March and think the frost is gone and spring is here, only to be hit be a deep freeze. You would think I would learn but I don't and I try to get plants out early. Yes... every year!
Your cool weather crops like; lettuces, spinach, kale, broccoli, cauliflower and peas can actually take a frost and a freeze into the upper 20's and survive. Now the cold can still damage them, so simple easy frost protection is always valuable. In this video, I talk about 17 degree and 20 degree F nights that came back to back. That is just too cold for newly planted transplants.
The freezes killed off my unprotected peas and lettuces but the plants that were covered by the rigid plastic cups survived nicely! I also used a large trash bag as a second layer of protection for one of my container planting of peas. Here is the method and proof it works. This is a quick and inexpensive way to protect your plants.