My canna's multiply every year and so does the debris (stalks and leaves). They don't seem to break down in the mulch pile and they are too wet to grind in a machine. What do I do with all the debris????
They will break down if you cut them into smaller pieces. I use a heavy pair of clippers to do so.
Chop them with a mulching lawnmower. Anything I want to chop up, such as plant stalks, I pile on the ground, run the gas mower over it, and empty the shredded stuff out of the bag. Fall leaves compost quicker when treated this way, and pine straw (dry needles) chopped up in this manner makes a fair mulch to keep slugs away from my hostas, although it doesn't discourage earwigs.