Why do cats eat grass? What we know and which plants are safe
Nobody knows for certain why cats eat grass, but it is normal and very common behaviour in healthy cats. The strongest theory is that it is an inherited behaviour that helped their ancestors expel intestinal parasites. What matters is that the grass is safe and that the cat cannot get at toxic plants such as lilies.
It is more normal than you might think
Many owners worry when they see their cat, a strict carnivore, nibbling grass or houseplants. It is very common behaviour. In 2019, Benjamin Hart and colleagues at the University of California, Davis, published the results of a survey of cat owners who could watch their cats for at least three hours a day. Of more than a thousand cats analysed, 71 per cent had been seen eating plants at least six times, and only 11 per cent never had. In other words, the vast majority of cats eat plants at some point, and most do so while perfectly healthy.
They don’t do it to be sick
A widespread belief is that cats eat grass when they feel unwell, to make themselves vomit. Hart’s survey doesn’t support this: according to the owners, 91 per cent of the cats seemed normal before eating plants, and only about 27 per cent were frequently sick afterwards. It is true that grass can irritate the stomach and that some cats bring it back up, sometimes along with hairballs, but most of the time they eat it and nothing happens. Vomiting would be more an occasional consequence than the aim of the behaviour.
The parasite theory
The explanation put forward by Hart and his team is evolutionary. Many wild animals, including chimpanzees and other carnivores, eat plants without digesting them, and this plant matter has been seen to help sweep intestinal parasites out of the body. The cat’s ancestors almost always had parasites, and eating grass regularly, as a preventive measure, would have been an advantage. Domestic cats, even though they are wormed today, would have inherited the behaviour. It fits with young cats eating more plants than older ones, and with cats doing it without being ill. It is a reasonable hypothesis, not a proven fact.
Other explanations on the table
Other reasons have been suggested, with less evidence behind them. One is that grass provides fibre that helps move swallowed hair through the gut and expel hairballs, which makes sense in longhaired cats, although it doesn’t explain why shorthaired cats eat plants too. Another is that it supplies a nutrient, such as folic acid, but a cat on a complete diet doesn’t need it. And the simplest factor shouldn’t be forgotten: many cats enjoy the texture of fresh grass, leaves that move and the game of biting. In indoor cats, boredom can also make them nibble the houseplants more.
Cat grass: the safe option
If your cat likes nibbling plants, the best thing is to offer a safe alternative. So-called cat grass is usually sprouted wheat, oats, barley or rye, sold in pet shops in pots or as grow-at-home kits for a few euros, and it grows in one or two weeks. Put it somewhere accessible, away from the litter tray and food bowl, and replace it when it dries out or turns yellow. Many cats prefer it to ornamental plants, which reduces the risk of them chewing others. If your cat eats it greedily and is sick every time, offer it in small amounts, for a few minutes a day, rather than leaving it within reach all the time. Catnip is something else: it is an aromatic plant that stimulates cats, not a grass for eating.
Dangerous plants: lilies come first
The real risk of a cat eating plants lies in the toxic ones. The most dangerous are lilies: biting a single leaf, licking pollen that has stuck to the fur or drinking the water from the vase is enough to cause acute kidney failure, which can be fatal within a few days. Houseplants as common as pothos, dieffenbachia, philodendron, aloe vera, poinsettia and the cycad or sago palm are also toxic to varying degrees, as are many outdoor plants such as oleander. Before bringing a plant into a home with a cat, check whether it is safe with Michipedia’s toxic plants tool.
When eating grass is a problem
A cat eating grass now and then is no cause for concern. It is worth seeing the vet, though, if it suddenly eats far more plants than usual, if it vomits often, several times a week, or if it is losing weight, has diarrhoea or seems listless. The same goes if it eats other things that are not food, such as plastic, fabric or paper, a behaviour called pica that can have medical or behavioural causes. And if it goes outdoors, bear in mind that the grass in gardens and parks may have been treated with weedkillers, insecticides or fertilisers. If it is vomiting and can’t keep water down, or is vomiting blood, it is an emergency.
How to protect your plants
If your cat insists on nibbling your houseplants, first remove all the toxic ones or put them in a room it can’t get into, because cats can reach almost any shelf. For the safe ones you want to keep, put its own, more tempting pot of cat grass within reach. You can cover the soil with large stones so it doesn’t dig or use the pot as a litter tray. Home-made repellents such as citrus or vinegar don’t work well, and some essential oils are toxic to cats, so it is best not to use them. More play and enrichment also cut down nibbling out of boredom.
Eating grass is normal in healthy cats: in a University of California, Davis study (2019), 71 per cent of over a thousand cats ate plants regularly, almost always without being ill, and only 27 per cent were often sick afterwards. It may be an inherited way of expelling parasites. Offer cat grass and keep toxic plants away, especially lilies.
Educational content from Michipedia, translated from the Spanish original. It does not replace the advice of a vet or a feline behaviour specialist. Every cat is an individual.