I apologize for the delayed reply. Spring is a busy time and I'm working hard on trying to catch up on a lot of questions!
Covering plants with a sheet or blanket supported to prevent it from crushing small plants is the best way to protect them. If you can keep the cover from touching the plants that is best but not always practical to do. Wait until late day to cover so the sun heats the soil and then cover for the night and remove it when temps are above freezing again the next day.
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