This reader has discovered companion planting onions with cole crops will discourage cabbage white butterflies.
I strongly recommend companion planting of cole crops and onions. Cabbage white butterflies are apparently repelled by the onion smell. The cabbage, broccoli, kale, and cauliflower in my garden have done well with thickly inter-planted onions. The onions are shaded, but they start to “bulb out” as the cole crops are harvested, and I generally view these onions more as an insect repellent than as dinner.
Jeanne Kay Guelke
Wynndel, British Columbia
“Walking” or “top-setting” onions might work well for this purpose, as these perennial onions produce clusters of bulbils that could be scattered among your cole crops. — MOTHER EARTH NEWS