Make plastic bottles rigid to use as a cloche by forming a reinforcing ring around edge Place cloches over young plants & keep bottle caps off during day to prevent heat build up. Replace caps at night to trap heat and keep plants warm.
Soda Bottle Drip Feeder for Plants - Water Plants with a Soda Bottle
UPDATE: This method killed my cabbage plants! ---- Sprinkle Baking Soda on Cabbages (and other Brassicas) to Thwart Caterpillars If those small green cabbage worms have been making Swiss cheese of your cabbage, broccoli, and kale plants, try this trick