Cat grass is grass which is cultivated for cats to eat. Cereal grasses like oat, rye, barley, and wheat tend to be especially popular choices for cat grass, as these grasses are very easy to grow, and safe for cats to consume. Some pet stores sell cat grass kits, allowing pet owners to grow grass at home, and others sell cat grass which has been cultivated, so that it is ready for use.

While cats are carnivores, they do like to supplement their diets with grass. There are several theories about why cats eat grass, ranging from nutrient content to curiosity. Grass certainly helps cats digest, and it can also help them bring up hairballs. For indoor cats who cannot hunt, cat grass can replace the partially digested vegetable materials which cats normally ingest through their prey. Not all cats eat grass, with some demonstrating considerable curiosity, while others ignore it.

People establish cat grass in their homes to distract cats from houseplants, which are usually off-limits, and to supplement the diet of their cats. Cat grass can also provide some environmental enrichment for indoor cats, who tend to become bored and frustrated because they cannot go outside. Some people also like to grow catnip, an aromatic herb which is very appealing to cats.

When growing cat grass, it is a very good idea to use a wide, low container with a sturdy base, so that cats cannot knock the container over while they eat. Unlike herbivores, cats do not have teeth which are designed for chewing grasses, so they sometimes need to tug very hard, which can cause the planter to fall over. Curious cats may also want to play with the container, which can result in a big mess if the container is especially tippy.

Some cat grass kits come with nutrient-rich mats which are filled with cat grass seeds, allowing the pet owner to simply moisturize the mat to get the seeds to germinate. This is much tidier than working with seeds and soil, with the mat simply being pulled out of the planter when the cat grass is exhausted. Other kits come with soil or another growing medium, requiring the user to mix the seeds with the soil and water them. In addition to buying specially-labeled cat grass, it is also possible to buy containers or flats of wheatgrass which are designed for juicing.

Growing cat grass is extremely easy: all it needs is moisture and a bit of sunlight. The young grasses can usually regrow several times after being nibbled down, allowing cats to get several weeks of enjoyment out of a single container of cat grass. For pet owners who are using cat grass to discourage cats from chewing on the houseplants, it is a good idea to keep the grass in a location far away from the other plants, and to verbally chastise cats when they attempt to snack on the houseplants, while praising them for investigating the cat grass.