No elk in my neck of the woods - thank the lord!! - I can only imagine what kind of damage these massive beasts could do a garden. Anyway, your request piqued my curiosity and I did a little research. Apparently all of the common ungulates (deer, moose, elk) will share a similar diet, so if deer will feed on it, elk likely will also. If hungry enough, deer will feed on just about anything, so availability of natural fodder will impact what ornamentals they may graze on. Also, deer at least have a bit of natural curiosity and they will sample just about anything but may not munch it down to the ground if a taste they don't particularly like. Not sure if elk share the same adventurous gourmet spirit.

Have you considered fencing?

Here is a link that might be useful: gardening with deer and elk