First Frost

Last Sunday I checked on garden plot #1 and the vegetation showed signs of wilt. The temperature had dropped into the 20s overnight. As I uprooted and examined the root ball for eggplant (healthy and multi-branched) and green pepper (small and shallow) a question formed:

If there is no humidity in the air, can frost actually form? Can vegetation skip the frost on leaves stage and go straight to frozen? The plant cells are filled with water. Water freezes then bursts the cell walls, which is what you see. So think about my science question.