Why Do Cats Eat Grass? The Salad Course, Explained

Cookie here, editor-in-chief. The humans asked me to explain why cats eat grass, presumably because they have watched me enjoy the garden buffet and then, on selected occasions, return it to them as a gift. Let me give you the short version first: grass eating is normal, extremely common, and the best scientific explanation is that it came with the species. It is not, in most cats, a sign that anything is wrong.

The long version involves two surveys, thousands of cat owners, a rejected hairball theory, wolves, and one flower that this magazine takes deadly seriously. Bring snacks. I will.

What 3,000 cat owners told the scientists

The backbone of everything we know here is a research program from a team at the University of California, Davis, led by Benjamin Hart. They first presented the work at an animal behavior conference in Bergen, Norway in 2019, then published it in 2021 in the journal Animals. Two separate owner surveys, run a decade apart, with the second one disguised among general behavior questions so plant-obsessed owners would not skew the sample. Clever. Sneaky, even. I approve.

The numbers, by survey, because they measured slightly different things:

Translation from the scientific: nearly everyone does it, nearly nobody looks sick first. The youngest cats are the most committed: under one year old, 93.4 percent ate plants weekly, and among cats three or younger, 39 percent did it daily against 27 percent of their elders. Kittens also branch out beyond grass, while adults settle on it like regulars at a favorite bistro. Sensible animals.

Priya · Health desk

The numbers deserve one precision, because the internet keeps repeating that cats eat grass in order to vomit. The surveys point the other way: only 6 to 9 percent of cats looked ill beforehand, and most cats, roughly two-thirds or more depending on the survey, did not vomit afterward at all. The one real pattern is age: among frequent plant eaters over nine years old, 57 percent were seen vomiting often. So it is not the reason most cats do it, and in an older cat a new grass-then-vomit habit is worth attention.

Cookie · Editor-in-chief

I said exactly that, only with more charisma. A gentleman enjoys his salad course and keeps it down. The occasional dramatic exception is called performance art, and the carpet was chosen for a reason.

The leading theory: a dewormer inherited from wild ancestors

So why do we do it? The Hart team's answer, and they are honest that the survey method cannot prove it, is that grass eating is an instinct inherited from wild ancestors, where fibrous plants helped carry intestinal parasites out of the body. A review they cite found plant eating documented across 124 wild carnivore species, cats' wild cousins included. Back in 1944, the biologist Adolph Murie examined wolf droppings in Alaska and found blades of grass wrapped around intestinal worms, and suggested grass physically scours them out.

The logic fits the age pattern too: in the wild, young animals carry the heaviest parasite loads and would benefit most from a regular fiber sweep, and in the surveys, young cats ate plants the most. Your modern indoor cat almost certainly has no worms to sweep. The instinct never got the memo, and honestly, why would it. It is a beautifully engineered system and I will not hear it criticized.

The researchers are explicit that the true confirming experiment has never been done and is not really feasible. So the correct phrasing is: best remaining explanation, not proven fact. We say it exactly that way on purpose. Rigor is a house specialty, like biscuits.

The theories that lost, and the one that just shrugs

The hairball theory, that cats eat grass to purge swallowed fur, got tested directly and failed. If it were true, long-haired cats should eat more grass than short-haired cats. They do not: 83 percent of short-haired domestic cats and 85 percent of long-haired ones had been seen eating plants more than ten times, with similar illness and vomiting rates around it. The paper's own conclusion is that the data do not support the hairball-purging hypothesis. A theory walked in confident and left in a doggy bag.

The vitamin theory, that cats eat grass to top up folic acid or trace nutrients, is often repeated and rarely sourced. Even the veterinary sites that mention it flag it as unconfirmed, and the Hart paper lists a nutrient deficiency only as an untested possibility. It might be true. Nobody has shown it.

And then there is the explanation that requires no laboratory: some cats simply like it. Cornell's feline health experts describe plant chewing as part of normal investigation and play, and in Survey 2, 35 percent of owners who kept a grass bed for a committed plant eater said the cat enjoyed eating grass. Enjoyed. Imagine needing a survey for that. I could have confirmed it for a modest fee, payable in tuna.

The real dangers grow next to the grass

Now the serious course, because the grass itself is rarely the problem. What surrounds it can be.

A treated lawn is not a salad bar. Veterinary guidance is consistent that cats should not chew grass treated with pesticides, herbicides or fertilizers: cats groom residue off their own fur, which turns a walk into a meal. Offer untreated grass or keep the outdoor grazing supervised.

Houseplants and bouquets deserve a full inspection, and one family is in its own category of dangerous. According to the US Food and Drug Administration, in true lilies and daylilies the entire plant is toxic to cats: stem, leaves, flowers, pollen, even the vase water. Eating a small piece of a leaf, licking a few pollen grains off fur, or drinking from the vase can cause fatal kidney failure in less than three days. Early signs such as low energy, drooling, vomiting and loss of appetite start within 0 to 12 hours. Our guide to plants toxic to cats covers the rest of the household jungle, lilies included.

One more physical hazard, small but documented: a grass blade can lodge in the passage behind the nose. A 1993 case series in the Journal of the American Veterinary Medical Association described eight cats with a grass blade stuck in the nasopharynx, each removed by a veterinarian under sedation. Sudden violent sneezing fits after a garden session, especially from one side, are covered in our cat sneezing guide, and they are a vet visit, not a wait.

The Vet's Take · Veterinary review

One part of this page is not funny, so I am taking it. True lilies and daylilies can kill a cat: a chewed leaf, a few pollen grains groomed off the fur, or a drink from the vase can cause fatal kidney failure, and the FDA notes that treatment delayed past about 18 hours generally means irreversible kidney damage. If a cat may have touched a lily, call your veterinarian or a poison control center immediately. Do not wait for symptoms.

Cookie · Editor-in-chief

For once, no counterargument. Lilies are banned from my building. Flowers that attack the kitchen staff have no place in a civilized home.

Cat grass: the indoor salad bar

If your cat has opinions about greenery and no safe garden, the answer is sold in trays: cat grass, which is simply young wheat, oat, barley or rye grass grown indoors, untreated and out of reach of anyone's weedkiller. Cornell's feline health center suggests offering oat grass, catnip or catmint to cats that crave vegetable matter, and even mixing a little lettuce or parsley into meals. A pot on the windowsill, sprouted in a week, and the houseplants get diplomatic immunity.

I maintain a personal tray. It is mine. The ficus was a negotiation; the wheatgrass is a treaty.

When grass plus vomiting becomes a vet question

Most grass eaters do not vomit most of the time, so a cat that eats grass and then throws up regularly is telling you something. The most specific published threshold we found comes from a board-certified veterinary behaviorist, Dr. Wailani Sung: throwing up more than twice a month after eating grass warrants a veterinary conversation. Veterinary sites frame it the same way qualitatively: a frequent or newly frequent pattern of grass then vomit can point at gastrointestinal disease or parasites, and earns an exam rather than a shrug.

The wider rules about vomiting apply here unchanged, and our cat throwing up guide carries them: repeated vomiting, blood, lethargy, refusing food, or a cat that just seems wrong are vet-now territory, grass or no grass. In the surveys, older cats vomited after plants far more often than young ones, 57 percent of frequent plant eaters over age nine, so a senior cat's new grass-and-vomit habit deserves particular attention.

What to take away

• Grass eating is normal, common cat behavior: in two UC Davis surveys, 65 percent of cats ate plants weekly (Survey 1) and 71 percent had been seen eating plants repeatedly (Survey 2).
• Cats are rarely sick beforehand: only 6 to 9 percent of cats appeared ill before eating plants, and most did not vomit afterward.
• The best-supported explanation is an inherited instinct from wild ancestors, where fibrous plants helped expel intestinal parasites; researchers class it as the strongest remaining hypothesis, not a proven mechanism.
• The hairball-purging theory was tested and rejected: short-haired and long-haired cats eat plants at nearly identical rates (83 vs 85 percent).
• True lilies and daylilies are the emergency case: per the FDA, a few pollen grains or a sip of vase water can cause fatal kidney failure in a cat, and treatment delayed past about 18 hours generally leaves irreversible damage.
• A cat that vomits more than twice a month after eating grass, per veterinary behaviorist guidance, should see a vet; so should any cat with sudden one-sided sneezing fits after a garden visit.