I tied a hefty string around the base of a green cabbage and hung it from a low slung branch in the run. What a hoot! That poor cabbage was picked down to a nub in a matter of hours. The coolest part is that as it decreases in size, the branch raises up. By the time it was half gone, they had to jump and fly a bit to get to it. Exercise and treat! I just bought another cabbage.
