I kind of agree with Paul....I plant mine in raised beds in rows, plants about 1 foot apart but rows probably around 2-3 feet apart. I place a trellis in between rows...You do mention green caterpillars. I can't recommend as I don't have the experience to do so, but I will say that I have had luck with Bacillus thuringiensis on my cabbage. It took 1-2 sprays, and from what I understand, it's fairly harmless (unless you drink it of course.). Maybe look that up.

How many plants are in there?

There's four in there and I'm positive it's too many :) Just trying to see if that's the issue that's causing the other issues or If they're seperate issues

I think thinning is one of the hardest parts of vegetable gardening. Its magical watching all of those little seedling pushing up through the soil. Then you have to decide which of your beautiful little babies to decapitate so the others will thrive. ;)

Again, I'm no expert, but I do know that if a plant is stressed one way or another, it will be much more much more prone to pests and diseases, such as succumbing to caterpillars. Proper spacing, which allows plenty nutrients for each plant, goes a long way. Even with thinning though, you will still have to fight these other diseases and pests that the plant has now taken on.

As Paul said, check if they're root-bound.

Pots are for patios, I'd start some late seed in the soil that container is sitting upon, looks like you have the space. Just keep it weeded. Thought for today ;-)

Since you already know they are way over crowded and probably root bound in the container why not cut 2 of them out of there and see if the other two don't bounce back? Nothing to lose.

Dave

Yeah Dave, thats what my thought was. Thanks for the quick responses everyone