You can train cats to use a litter box, but many cats may prefer your house plants. Follow these steps to break this habit.
Make it Stinky
Sprinkle red pepper or cayenne pepper in the dirt around your plants. You will have to use a lot of it so when your cat digs, the powder goes into their nose and causes discomfort.
Take citrus rinds, grind them up in your blender and place them into the soil around your plants. Since citrus rinds do break down, you'll have to keep an eye on them so they don't mold.
Buy a commercial repellent from your pet store. The odor may be enough to keep your cat from urinating in your plants.
Make your own anti-cat recipe. Combine 2 parts cayenne pepper, 5 parts flour and 3 parts dry mustard. Sprinkle liberally onto the dirt.
Save your tea bags, cut them open and sprinkle the leaves into the soil.
Cover the Dirt
Put rocks over the soil to prevent cats from digging and urinating in the soil. Use large rocks rather than small pebbles that mimic the sand in the litter box.
Cover the dirt with aluminum foil. Though it may not be aesthetically pleasing, it will stop your cat from urinating on the plant.
Place netting on top of the soil from a craft or fabric store. With the netting in place, you can still water and put fertilizer on your plants, and your cats won't be able to dig in the dirt. Cats are clever though, so keep checking to make sure your pet hasn't figured out a way to lift the netting.
Catch your Cat in the Act
Squirt your cat with a squirt bottle if you catch them sniffing around the plant.
Bang a newspaper on the floor so they associate the crinkling sound with the plant pot.
Yell at them. Most cats will respond to the sound of a firm voice, especially if they're doing something they know they're not supposed to do.