Looking at my collards and kale now, it doesn't seem like a good idea- the large leaves of those plants go right out from the base and rest on the ground. What is you location (state or country), and when would you be planting/harvesting these? I started some arugala between the spent sweet corn stalks this year that did ok.

collards close canopy much better than kale. But I would not interplant either. Maybe interplant cabbage, which is slow, with something like lettuce, which is fast and gets out of there before cabbage close canopy too.

I interplant lettuce when the brassicas are first set out and are still small. But in my climate I can grow lettuce all summer. That may not be possible in hotter places. By the time the kale etc. is big I have harvested the lettuce.

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

Sorry I didn't reply earlier! I couldn't find my post :( We're in the niagara region of southern ontario. I'll be planting both as soon as possible in the spring. Not sure when exactly because the may 24 rule doesn't seem ideal anymore lol

I second lettuce, mini bok choy scalions, corn salad....