A dog that eats grass is, in the vast majority of cases, showing normal and common behaviour that is usually neither a sign of illness nor a way of making itself sick. You should, however, pay attention if it suddenly eats much more, vomits repeatedly or shows other symptoms: in those cases, see your vet. On walks, the real risk mostly comes from what is on or in the grass: pesticides, toxic plants, grass seeds and parasites.
Why a dog that eats grass is not necessarily ill
The popular belief is that dogs eat grass because they have a stomach ache and want to vomit. The available studies do not back this up. The most cited was carried out at the University of California, Davis (UC Davis) School of Veterinary Medicine by Karen Sueda, Benjamin Hart and Kelly Cliff, and published in 2008 in the journal Applied Animal Behaviour Science. It is based on two surveys:
- Clients of the veterinary hospital: of 47 owners of healthy dogs with daily access to plants, 79% had seen their dog eat grass or other plants.
- Online, among owners of plant-eating dogs: of 3,340 questionnaires returned, 1,571 met the criteria. 68% of the dogs ate plants daily or weekly, and grass was the most commonly eaten plant (79% of dogs). Only 9% of dogs frequently seemed unwell beforehand, and 22% frequently vomited afterwards.
The researchers also found that younger dogs ate plants more often, while appearing unwell beforehand and vomiting afterwards less often. Neither sex, neutering status, breed group nor type of diet was linked to how often the behaviour occurred. Their conclusion: plant eating is a normal behaviour of domestic dogs.
These findings have limits. They are owners’ reports, not veterinary observations. The online survey targeted people interested in the subject, recruited through websites and forums, and excluded dogs with medical problems or medication that could cause vomiting or increase appetite. It therefore describes healthy dogs: it does not show that an unwell dog never eats grass because it feels ill.
The suggested explanations
Nobody knows for certain why dogs eat grass, and several causes may combine. These are the ideas put forward by researchers and canine organisations:
- Hunger. In a small Australian experiment (Bjone, Brown and Price, 2007, University of New England), 12 dogs were offered grass three times a day for six days. They ate more of it before their meal than after, and less once full, which suggests grass may partly serve as food. The sample is very small.
- An ancestral habit. Sueda and colleagues point out that plant matter, especially grass, is regularly found in the droppings and stomach contents of wolves.
- Taste and texture. The UK’s Royal Kennel Club notes that the behaviour seems more common from April to August, perhaps because the taste, texture or smell of grass changes with the season.
- Fibre. The American Kennel Club (AKC) mentions a possible need for fibre. The Royal Kennel Club cites a dog that had eaten grass and vomited regularly for seven years and stopped after moving to a high-fibre diet. A single case does not apply to every dog, and any change of diet should be discussed with your vet.
- Boredom. A dog lacking stimulation may chew grass, just as it digs or chews other things (AKC, Royal Kennel Club).
- An empty stomach. According to Dr Jerry Klein, the AKC’s Chief Veterinary Officer, vomiting yellow foam (bile) usually indicates an empty stomach; some dogs may then eat grass.
Dog eating grass and vomiting: when to worry
A dog bringing up a little grass now and then after eating it is generally nothing to be alarmed about. The Royal Kennel Club and the AKC do, however, advise contacting your vet in the following situations:
- it eats grass but no longer eats its food;
- it eats it in large amounts or obsessively, or far more than before: a sudden change deserves attention;
- it vomits repeatedly after eating grass;
- it shows other signs: diarrhoea or constipation, blood in the stools, weight loss, reduced appetite, unusual tiredness, repeated lip licking;
- you think it has chewed a toxic plant or treated grass.
If the behaviour becomes extreme, the vet may consider pica, the compulsive eating of non-food items (stones, soil, fabric), and look for a medical, dietary or behavioural cause (AKC). Only your vet can tell. Note the frequency, the quantity, what the vomit looks like and any other symptoms: this information will help.
The real risks of grass on walks
The danger lies less in the grass itself than in what comes with it:
| Risk | What the sources say |
|---|---|
| Pesticides, herbicides, fertilisers | The Royal Kennel Club says a dog should never be allowed to eat treated grass; the AKC points out that these products can be toxic. |
| Toxic plants | The ASPCA list classes, among others, lily of the valley, oleander, yew, foxglove, autumn crocus, daffodil, tulip, azalea, ivy and castor bean as toxic to dogs. |
| Parasites | Intestinal worms (roundworms, hookworms) from other animals’ droppings (AKC); lungworm spread by slugs and snails that have crossed the grass (Royal Kennel Club). |
| Grass seeds | They lodge in the ears, eyes, between the toes or under the arms, and can migrate under the skin (PDSA). |
Grass seeds deserve particular attention. PDSA, the UK veterinary charity, recommends checking your dog after every walk in long grass and seeing your vet if a seed is stuck or if a wound or swelling could be hiding one. Signs to look out for: head shaking, a weepy eye, persistent licking of a paw, swelling between the toes. Use this check to look for ticks too, as explained in our article tick on a dog: what to do. Against parasites, regular worming agreed with your vet remains the foundation: the Royal Kennel Club considers eating a little grass normal for a healthy, regularly wormed dog.
If you suspect poisoning (a plant, a lawn treatment), call your vet or a veterinary poisons service straight away; we cover the right reflexes in antifreeze and dogs: what to do in case of poisoning.
Managing it on the lead without spoiling the walk
There is no need to forbid every mouthful of grass for a healthy dog. The aim is rather to choose where it eats grass and to avoid excess. If your dog also picks up everything it finds on the ground, the “Leave it” cue is explained step by step in dog eats everything outside. For grass, a few habits are often enough:
- Know which areas to avoid: lawns you are not sure are untreated, the edges of cultivated fields, roadside verges, flower beds and ornamental hedges where toxic plants grow.
- Shorten the lead when crossing these areas, and in summer in long, dry grass; give it more length again on grass you know.
- Offer something better: a toy or a more interesting treat when it starts grazing insistently (AKC).
- Think about the empty stomach: the AKC suggests smaller, more frequent meals, especially in the morning, for a dog that eats grass on an empty stomach.
- Keep its nose busy: a longer or more varied walk, with time to sniff, helps a bored dog (Royal Kennel Club). Our guidance on how long to walk your dog will help you adjust.
A well-fitted harness makes these changes of direction more comfortable than a collar, especially if the dog insists; the handle on the models in our harness collection lets you keep it close while you pass a treated area.
Frequently asked questions
My dog is suddenly eating grass frantically: what should I do?
A sudden change warrants veterinary advice, especially if it comes with vomiting, lip licking, loss of appetite or a dog that seems low. In the meantime, stop it eating more grass and note what you observe.
Should I let my dog eat grass so it can make itself sick?
No. Most dogs do not vomit after eating grass, and a dog that seems to have a stomach ache should be seen by a vet rather than left to “treat itself”.
My puppy eats a lot of grass: is that normal?
In the survey by Sueda and colleagues, younger dogs ate plants more often than older ones. Keep an eye above all on what else it swallows and where it grazes.
Sources
- Sueda K.L.C., Hart B.L., Cliff K.D. (2008). Characterisation of plant eating in dogs. Applied Animal Behaviour Science, 111, 120–132.
- Bjone S., Brown W., Price I. (2007). Grass eating patterns in the domestic dog, Canis familiaris. Recent Advances in Animal Nutrition in Australia, 16, 45–49.
- Meyers H. (2026). Why Does My Dog Eat Grass? American Kennel Club.
- The Royal Kennel Club. Why does my dog eat grass? The Royal Kennel Club.
- PDSA (2020). Grass seeds in dogs. PDSA Pet Health Hub.
- ASPCA. Toxic and Non-Toxic Plant List – Dogs. ASPCA Animal Poison Control Center.