House plants that are toxic to cats

I didnt know that!

Eating house plants is a common behavior in cats that do not get vegetable matter in their diet. 

Listed here are plants poisonous to cats that must be avoided if there are cats in your home. Note that lilies, in particular, are dangerous to cats. While in some cases, just parts of a plant (bark, leaves, seeds, berries, roots, tubers, spouts, green shells) might be poisonous, this list rules out the whole plant. If you must have any of them, keep them safely out of reach.

http://goodcats.com/toxicplants.html

Try this :
By providing a small flower pot with grass or catnip, an owner often can eliminate the problem. For the cat that has developed a habit or preference, putting the plant where the cat cannot get to it or using aversive taste-smell conditioning with pepper sauce or vinegar usually works. You can also use a fine mist water sprayer at the cat when caught in the act or other scare tactics like making a loud noise to startle it.