Perhaps someone else can chime in on this, but other than covering the cabbages with a floating row cover (works as long as you do it before you see the cabbage moths) or using BT, does planting the purple variety allow you (and the birds) to see the caterpillars on the plants? Hmmm. I’ll have to try that this year. Maybe some purple broccoli, too.
The Problem: How can I keep the caterpillars off my cabbage?
The Hack: cover your cabbage crops with a floating row coverto keep the caterpillars away.