What kind of problem are you having with green leaf vegetables? Do they not grow or they bolt? Most leafy greens can be grown for fall crop where you are and they do very well in the cooler weather of fall and early winter.

cabbage - leaves are chewed mostly, but it also does not mature fast enough before the heat comes
seed germination of cold weather leaf crops is very low and those that germinate - do not mature

Jolly, in your locale, plant chard in the spring, and plant kale in August. Everything else you try is too sensitive to heat. This year (a warm year in MI) I am doing well with cabbage, but I planted half of it early in part shade(and now it is not growing but it is already of decent size), and the other half in full shade. You can also plant radicchio in June-July or collard 3 weeks before kale.

For the leaves of brassicas being chewed, you will have to use BT or tulle netting. There is no defense otherwise. All these greens except radicchio appreciate abundant fertilization, water and wood ash side dressing.

cabbage worm is probably what you have. Try floating row cover, BT and rotate your crop. When did you transplant your cabbage and kale outdoors? Around where you are, you can transplant in late March.