Cats love to do things that don’t make sense to us. Something that all cat owners notice sooner or later is that cats have an odd habit of chewing on grass. But is chewing grass good for a cat, or a sign of poor gastrointestinal health?

Why is my cat eating grass? Cats may eat grass because it’s nutritious, to clear their guts of parasites, or just because that’s what they were taught. Regular grass is safe for cats to eat, so long as it doesn’t have pesticides or weed killer on it. If you want to stop your cat eating grass, buy it cat grass (a kind of potted plant that contains many safe grasses for cats to chew on). Catnip and mint are good alternatives.

The guide below first looks at why cats eat grass to begin with: whether it’s a quirk of evolution, something cats have been taught, something necessary for their diet, or an adaptation to get rid of internal parasites. It will then address the important question of whether it’s safe for cats to eat grass, and why some plants are toxic and others aren’t. Finally, it will give you some hints on what to do if your cat won’t stop eating grass no matter what you try.

Why Do Cats Eat Grass?

You might think that your cat eating grass is unusual and wrong, and something you need to correct. But that’s not necessarily the case! There are actually several reasons why cats eat grass, which are detailed below.

1) Do Wild Cats Eat Grass?

Grass-eating isn’t a behavior that your housecat has developed, and which isn’t seen in any kind of wildcat. It’s actually common in nature, despite the fact that cats are obligate carnivores, i.e. they have to eat meat.

When you think about it, cats are forced into eating grass, leaves, and other similar substances. That’s because they eat small rodents, and small rodents eat grass and other plants. When your cat eats these rodents it eats whatever is in the rodent’s gut, too. Some of this will be partially digested, but some will be almost raw, and the cat has to deal with this plant matter by putting it through the rest of the digestive process. So while cats are best at digesting meat, they need to be able to digest plant matter, too.

Wild cats are also known to eat plant matter without meat, too.

What’s more, this partially digested plant matter isn’t just an annoyance to a cat. It’s beneficial.

2) Eating Grass Helps a Cat’s Upset Stomach

But besides eating a small salad with its meal, your cat sometimes goes out and actively finds grass to chew on. So while it makes sense that your cat would get some greens in its diet because of the prey it eats, why would it look for grass to feed on?

The most common theory is that cats eat grass to help them bring things up. The idea is that the cat’s digestive system isn’t used to eating grass; while they do get some in their natural diets, it’s definitely not a regular food. It can stimulate the gut to pass things either way, which is particularly useful in cases of:

• Bones and feathers in the stomach. Cats can experience blockages from their normal diet. Their stomach acid isn’t strong enough to break down either bones or feathers, so they can get stuck. Again, stimulating vomiting can assist with this.
• Hairballs. Hairballs form during the course of normal grooming. Cats pick up hairs with their tongues as they lick their coats, and some of these are swallowed by accident. If these can’t be passed through the stool, or brought up by coughing, they form large matted balls.

Stimulating the vomiting reflex is what most owners attribute grass-eating to. According to the Royal Society, though, this likely isn’t the primary reason:

In veterinary clinical practice, the traditional explanation for plant-eating in dogs and cats is that there is a dietary deficiency or that plant-eating is a way of inducing vomiting. In two broad-ranging Web-based surveys of thousands of dog and cat owners, it was found that the great majority of dogs and cats appeared normal before and after eating plants and did not vomit.

Scientists therefore think that eating grass actually serves many more purposes than settling an upset stomach.

3) Cats Eat Grass to Expel Intestinal Parasites

If your cat’s gut is full of worms, then eating grass can supposedly help get rid of them in various ways. One way would be to stimulate vomiting or diarrhea. But it also seems like the fibrous plant matter, which isn’t properly digested in the cat’s stomach, can actually entangle the worms and force them out of the gut:

In his field studies, the noted wolf biologist, Murie, described seeing leaves of grass wrapped around expelled intestinal worms in wolf scats, suggesting that plants purged or expelled intestinal worms. … Evidence that regular consumption of non-digestible plant material occurs in wild canids and felids is that grass and leaves have been found in a range of 2–74% of scats and stomach content samples of wolves and cougars.

What’s interesting is that cats likely do this as a preventative measure:

Just as humans cannot feel worms in their intestines, dogs and cats (and their wild ancestors and relatives) presumably cannot feel, or otherwise know, whether or not they are infected with worms, aside from a vague stuffed feeling. The evolution of regular plant-eating by canids and felids is arguably an adaptive ongoing strategy for maintaining the intestinal parasite infection at a low to moderate level.

It’s thought that kittens eat more plants than adult cats because they’re particularly susceptible to parasites. The reason for that is that kittens are much smaller, so worms have a comparatively larger effect on them. In the wild, animals regularly fail to thrive because they have such large worm infestations. But your kitten doesn’t know it lives as a pet, so it eats grass anyway!

4) Fiber Acts as a Natural Laxative

Grass can stimulate your cat’s digestive system in ways that meat can’t. That’s because grass contains lots of fiber, which encourages your cat’s gut to work harder.

So, as stated above, cats can eat small amounts of grass without throwing up. Otherwise, they could never eat their rodent prey. Grass, like all plant matter, contains fiber; meat contains none. While a cat’s gut can’t break down fiber—it specializes in meat, not plant matter—the fiber nevertheless helps your cat form a healthy stool. Fiber also stimulates the gut to move along quicker, useful if your cat is struggling to go to the toilet.

5) Grass Contains Folic Acid

Even though it has a reputation for being bland, boring and non-nutritious, grass contains a surprising amount of nutrients. That includes vitamins and minerals that are beneficial to cats.

One of these micronutrients is folic acid. Folic acid is found in a cat’s mother’s milk, so we know for sure that cats need it! It helps digestion, supports the growth of cells, and is essential for the production of hemoglobin (which is responsible for transporting oxygen through the bloodstream).

It’s thought that cats may feel the urge to eat grass when they’re deficient in certain vitamins, in the same way as pregnant women seek out unusual foods! This is especially relevant for cats which experience long-term deficiencies, which can occur because of incorrect diet or tapeworms.

Is It Safe for Cats to Eat Grass?

Grass is perfectly safe for cats to eat, although there are a number of caveats you have to be aware of.

Fertilizer, Herbicides & Pesticides

Normal wild grass is fine. But if your cat is eating garden grass, that could be a major problem.

That’s because of the things you put on the grass to help it grow, or to kill weeds. Fertilizers, herbicides and pesticides all shouldn’t be ingested. If your cat does ingest them it could become sick. This wouldn’t be a problem for a wild cat, but it is for an urban pet.

This is something that’s within your control. If your cat won’t stop grazing on your lawn, then you can at least ensure you don’t use any harsh pesticides or fertilizers. In the case of fertilizer, you could also make sure to wash it away before letting your cat out.

Toxic vs. Non-Toxic Plants

Your cat may also take it upon itself to chew up the rest of your garden. But while normal grass is safe for cats, lots of other plants aren’t, and could hurt or even kill your pet. If you’re unsure whether a certain plant is toxic or non-toxic for cats, check the ASPCA list.

This also applies to houseplants. There are lots of houseplants that are toxic to cats. Kalachoes and lilies, for example, are poisonous to cats. Other plants like ferns are fine. If you’re not sure whether a plant is safe for your cat to eat, err on the side of caution. And if your cat eats something potentially poisonous, be that a houseplant or something from the bin, then you should take it to a vet as soon as possible. The vet can also tell you which plants are safe and which are poisonous.

Grass Can Get Stuck

Another problem with grass is that on rare occasions, it can get stuck inside a cat’s nasal chambers. It can get stuck there and make your cat sneeze excessively, trying to clear the blockage. It may not be able to, in which case you would have to take it to the vet, who can manually remove it.