Interesting, but I'm not sure I'ld really use it as it stands right now...
I think it would be much more viable if you flipped the abilities. I.e. have it turn into a compost heap when killed and make the deep roots ability the activated ability (i.e. random permanent destrcution on a stick).
Since the destruction is random, it should stay pretty well balanced.
E.g. you could use:
"Rot: Spawns a compost heap upon death.
: Deep Roots
Destroy a random permanent."