Eating plants is an exceedingly dangerous habit as many household plants are poisonous. If your cat is developing a habit of eating plants, you must separate the two until the problem is solved. Either remove the plants or confine your cat to an area with no plants. Do not delay. One good meal of the common houseplant Dieffenbachia is usually the last meal your cat will eat. Consult with your local nursery and do not keep poisonous plants in your house. There are so many non-poisonous plants to choose from, why take the risk? Even if your cat is well-trained, no cat is perfect and all it takes is one mistake for disaster to result.
If your cat loves to munch on greenery, do not deny him this pleasure. Instead, provide him with his very own special Kitty Garden. There are many commercially available kitty herb gardens for this purpose.
Do not assume that your cat will automatically dine in his new garden. It's best to teach him that this salad bar is intended specifically for his consumption. Call him over to the plants. Tempt him by waggling some of the leaves in front of his nose. Make them irresistible by garnishing them with salmon, or whatever meets his fancy. When he does eat, praise him lavishly. Let him know that this is a special treat just for him.
When your cat is regularly eating from his own garden without your encouragement, it is time to bring your plants back into your house and to teach your cat to stay away from them.
Start with one luxurious sample that is edible. Paint the underside of the leaves with an excruciatingly hot chile oil. Then spray the top of the leaves with a perfume diluted about 1:100 with water. You don't want your entire house to smell like perfume, you just want the plant to smell of it to your cat's very keen sense of smell. Place the plant in the middle of the living room floor and let your cat investigate.
Make the plant more irresistible by tying a length of string to a couple of leaves and tugging from a distance. This will entice your cat to approach and hopefully take a bite. At this point, he should dash off in search of his water bowl. Over the next week, move the booby-trapped plant to different locations in your house. Spruce up the hot sauce and perfume daily. When it's clear that your cat is no longer interested in this plant, bring in a second one and give it the same treatment. If it remains untouched, then you can bring the rest of your plants in, one a day. Spray them with the diluted perfume. At this point it is no longer necessary to use the hot sauce since your cat has already learned that the scent of the perfume means the plant is hot. Regularly spray your plants with the diluted perfume. Throughout this procedure, remember to encourage your cat to eat the plants from his own kitty garden.