I've been feeding Chili, my Russian, mostly grasses and weeds and hibiscus, with some tort-kibble mixed in with it so far... Would he also benefit from the occasional addition of squash or sweet potato?
Yes; I'm giving Addy a bit of sweet potato today, in fact.
I like to give her something orange once a month or so; there has to be something in them you can't get from leaves. Squash, sweet potato, a piece of red bell pepper, the top of a carrot. Some people feed them these foods more often than I do and I imagine it's fine. I don't give much do to the sugars.
Russians aren't grass eaters; if he eating that?