What part of Mums do squirrels and chipmunks eat?

We just planted three large mums, and the squirrels and chipmunks have
already decimated them. They climb on top and borrow in, they uproot and
dig up branches. And they always seem to be chewing on something -- I
can't tell whether they are eating petals, flowers, buds leaves, stems or
roots, but they are definitely partying.

We also planted a mum last year, but this is the first time that we had this
problem.

- David