And now this year the problem is seriously bad! I've now got all three types of caterpillar running riot over my PSB (looks really sickly) and my purple curly kale (looks healthy). Don't ask me what the 3rd type of caterpillar is (the others are the 2 types of cabbage whites). Gad they are just everywhere. 
I tried an experiment I'd read about - apparently the butterflies don't like the smell of broom (the plant). So I cut a load off my wild bushes and laid them all around the plants. The conclusion? - it doesn't make a blind bit of difference!
I know this sounds daft, but do you think that attracting butterflies with the kind of flowering plants that they like is attracting them to come near my brassicas?
It's the only thing I can think of, as I have gazillions of Verbena Bonariensis that just self seeds everywhere and is coming up through all the unweeded bits of my veg patch, like in amongst the melons. In other parts of the garden (flower beds) the cabbage whites are all over these plants along with the other butterflies. Wondering whether the fact that I've got them IN the veg patch is attracting the butterflies into it, then they spot the brassicas? Hmmmmmmm. 
(thanks)
Is it dry where you are Mrs M cos trying to find the time to do caterpillar patrol every day as well as spending ages doing all the watering is just too much sometimes. 
