Loosely blouse row cover over the planted area. and secure the edges with boards or soil so that the cabbage butterfly can't get undeneath it.

Row cover is a very lightweight non-woven "fabric" which allows light, air, and water to penetrate. It should be available in local garden centers and/or farm stores.

I read on the web about putting a nylon stocking over cauliflower/broccoli heads to prevent the moth/butterfly from laying their eggs on the plant. Has anyone tried this? I have yards to fine tuille material - if I fashioned a 'head' cover from it would it do the trick? I'd like to go organic if possible. thank-you.

You could spend a lot of time and energy placing nylons on your cole (cabbage family) plants but the floating row cover is easier and probably more effective.

Not 100% certain but I think the eggs are laid before the heads form. In that case you need to cover the plants before the heads start appearing. Several times I have noticed the small heads eaten befor they start expanding.

Absolutely. The best time to put floating row covers over the plants is right after they are put out in the garden. If you wait until you see the wee white butterflies that could be the adult imported cabbageworm or the gray moths that are the Adult Cabbage Loopers it is too late for those Floating Row Covers.