In my post soliciting “Luddite moonshots” Kyle replied, “How to grow any sort of brassica or leafy green without having to constantly poison these jerks. I opted for none of the above this year because it is so demoralizing.” Then he linked to the Wikipedia article for the banana slug.
While we have no banana slugs down here in the southern reaches of California we have plenty of other brassica and leafy green pests, principally the cabbage leaf worm. I’ve come to much the same conclusion as Kyle and grow only arugula and lettuce during our cool winter season. I leave the kale cultivation to the professionals. There’s nothing wrong with growing the crops that do best in your climate and passing on the rest. The nicest brassicas I’ve ever seen were on a farm in perpetually foggy and cool Bolinas, California.
That said, I had one season of flawless leafy greens through the combination of rich compost and row cover, specifically Agribon 15. The row cover thickness you use will depend on your climate. I opted for the lightest available as we often have freak heat waves in the winter here.
But I haven’t deployed any row cover in years. It’s a pain to use. You have to be diligent in making sure the whole bed gets covered and it’s hard to see the plants under the cover without having to pull it on and off. And row cover won’t prevent slugs. Here’s UC Davis’ advice for dealing with slugs and snails. LA’s abundant mouse and rat population keep our snails and slugs in check. We can send you some if you’d like.