Ironically, Grundy's body is, like Ivy's, mostly plant matter (just not living plant matter). That's why the original Green Lantern's ring - being ineffective against wood - didn't work against him when the villain first appeared.
It may have been fast, but you were 100% right on the "fun." Never thought I'd enjoy a pun so much...Nor did I think I'd ever seen Ivy so defenseless and on the run. Normally even Batman has to watch his step with Ivy, so these zombies are really turning my world upside down right now.
On the plus side, it seems like zombies are really moving up in the world with this new veggie philosophy...Shame Ivy has to be around when they finally did so.