Sounds like they might be imported cabbage worms. (Imported from England, thank you very much.) Other control methods I've heard about in addition to the more effective ones stated above: Spread corn meal around the plants (the caterpillars are supposed to eat it, swell their stomachs, and die) Catch the moths with a butterfly net Get kittens who love to catch the moths and eat them :) Before eating the leaves, soak in salt water (so the caterpillars will die and fall off and you won't have to eat them.) DEFINITELY more of a problem with weak plants. I had kale growing two different places, one with much better soil. The caterpillars barely noticed the healthier plants, and they had apparently gotten under my row covers over the less healthy plants, and the result was an absolutely comical stripping job (I could laugh because I had the healthy kale in the other bed :) ) I've had kale plants produce for years without bolting or flowering, so you may well find a nice spring crop of collards growing from the old stems. Also, when it gets cold is when those nasty things finally die, and you get pest free leaves again! Next year try waiting before you cut the plants and see if the leaves clear up.

I'm not sure where you are or how hot it gets? You also didn't mention if you want to grow these greens during the spring/summer/fall/winter? I sometimes have luck growing some of the greens under a green bean "tent" to shade things during the summer. Other times it just gets too hot!I also have a shady area that those kinds of things do well in. Most greens in my area (8ish, No CA) do great in the fall/winter/spring. A little info would be great! Nancy

I let them get 2 to 4 true leaves. Then I break apart the soil very carefully so as not to damage the roots. I do the "hunk of seedlings" method (breaking off a chunk of soil and seedlings and planting the whole chunk). Then after they've had a few days to establish, I use scissors to cut off all but the healthiest. Needless to say, it's a bit wasteful, but it's easy, early and works for me. I always have plenty of lettuce seeds. lol. For kale and collards as well as the other cole crops, I plant each seed individually in a paper pot in milk jugs. One jug holds 12 of the newspaper pots I make. Then it's easy to pull the pots apart and plant them when I'm ready. Lettuce could probably be done the same way, but I haven't tried it.

I'd harvest as long as it is tasty.