If you’ve ever watched your dog stop mid-walk to munch on a patch of grass and asked yourself, “Why does my dog eat grass?”, you’re far from alone. Grass eating is one of the most common behaviours dog owners ask about — and one of the most surrounded by myths. You might have heard that dogs eat grass because they’re feeling sick. Others say it’s a missing nutrient, or a sign that something is “wrong.”
The reassuring truth? For the vast majority of dogs, eating grass is completely normal. But as clinical animal behaviourists, we think it’s worth understanding why dogs do it. Occasionally, a change in grass-eating habits can be the first clue that something medical or behavioural deserves attention.
At a glance:
For most dogs: eating grass is normal, common, and not a sign that something is wrong.
Why they do it: it seems to be a natural, ancestral behaviour – often simply wanting to eat something, not a way to make themselves sick.
Vomiting: around one in five dogs vomit after grazing, but this is usually incidental rather than the reason they ate it.
Worth a vet check: a sudden change, frantic grazing followed by regular vomiting, or other signs of illness such as weight loss, diarrhoea or lethargy.
The behaviour angle: rarely, compulsive grass eating is part of a wider anxiety or compulsive pattern worth assessing.
Why Does My Dog Eat Grass?
Research into grass eating has grown in recent years, and the findings might surprise you. A large-scale survey of over 1,500 dog owners found that most dogs ate plants regularly – around 68% on a daily or weekly basis. Grass was by far the most commonly eaten, and only 9% of dogs appeared unwell beforehand. About 22% – roughly one in five – vomited afterwards. Younger dogs were the most frequent grass eaters and the least likely to show any signs of illness.
So if they’re not doing it because they’re sick, why are they doing it?
- It’s a natural, ancestral behaviour. Grass eating has been observed in wolves and wild canids, and studies have shown that even very young puppies will eat grass when given the opportunity. It appears to be innate rather than learned, though puppies with mothers who eat grass frequently tend to do it more themselves.
- It may serve as a food source. Controlled experiments have found that dogs eat more grass before meals than after, and less grass when they’re full. This suggests grass may be seen as a supplementary food rather than a remedy for illness.
- It’s usually not to make themselves sick. The popular idea that dogs graze in order to bring on vomiting isn’t well supported: only around 9% seem unwell beforehand, and when researchers gave dogs a mild gastrointestinal upset they ate less grass, not more (McKenzie et al., 2010). A fair number do vomit afterwards – roughly one in five in the large survey – but this looks incidental rather than the point of eating it.
- Fibre and digestion may play a small role. In rare cases, dogs with a persistent, daily habit of grass-eating followed by vomiting have responded to a switch to a higher-fibre diet. But this is the exception, not the rule.
What to Do When Your Dog Eats Grass
For most dogs, grass eating needs no intervention at all. But here are a few things worth considering:
- Check what they’re eating isn’t treated. If your dog grazes on grass in parks, gardens, or public spaces, be aware of pesticides, herbicides, or fertilisers that could be harmful. Avoid areas that have been recently treated.
- Make sure their diet is meeting their needs. While grass eating is rarely caused by dietary deficiency in well-fed dogs, if your dog is eating grass obsessively and frequently, it’s worth reviewing their diet with your vet — particularly the fibre content.
- Watch for patterns. Occasional grazing is normal. But if your dog has recently started eating grass much more often, or is eating it frantically and then vomiting, that change in pattern is worth noting and discussing with your vet.
- Don’t punish it. Telling your dog off for eating grass won’t help and may cause anxiety around an otherwise harmless behaviour. If you need to redirect them, use a cheerful “let’s go” and reward them for moving on.
When to Speak to Your Vet
This is where the medical and behavioural sides of the picture overlap — and why having a team that understands both matters. While occasional grass eating is normal, there are some patterns that warrant investigation:
Medical Signs to Watch for When a Dog Eats Grass
- Your dog is eating grass frantically and vomiting regularly — this could indicate nausea, acid reflux, or a gastrointestinal issue that your vet should investigate.
- The grass eating is new, sudden, and obsessive — a rapid change in any ingestive behaviour can point to an underlying medical condition.
- Your dog is also showing other signs of illness — weight loss, diarrhoea, lethargy, changes in appetite, or excessive lip licking and swallowing.
- You suspect your dog has eaten grass treated with chemicals — contact your vet promptly.
Your vet can rule out gastrointestinal conditions, dietary issues, and other medical factors. This step is always worth taking before assuming the behaviour is “just behavioural.”
When Behaviour Plays a Part
Occasionally, grass eating — particularly when it’s compulsive, repetitive, or impossible to interrupt — can sit within a broader pattern of anxiety-driven or compulsive behaviour. Dogs who eat grass alongside other repetitive behaviours (such as excessive licking, pacing, or fixating on shadows or lights) may benefit from a combined medical and behavioural assessment.
At Second Nature Behaviour, our team includes a Veterinary Behaviourist who is qualified to assess cases where medical and behavioural factors overlap. This means we can look at the full picture — your dog’s physical health, emotional state, and behaviour — and work with your vet to develop a plan that addresses everything, rather than treating the behaviour in isolation.
The Bottom Line
Grass eating is one of the most normal things your dog does. It’s been part of canine behaviour for thousands of years, and for most dogs, it’s simply part of exploring the world with their mouth. Unless the pattern changes, your dog seems unwell, or the behaviour becomes compulsive, there’s usually nothing to worry about.
If you’re concerned about your dog’s behaviour, Second Nature Behaviour can help. Get in touch with us for advice, or ask your vet to refer you for a behaviour consultation.
References & Further Reading
Bjone, S.J., Brown, W.Y. & Price, I.R. (2007). Grass eating patterns in the domestic dog, Canis familiaris. Recent Advances in Animal Nutrition in Australia, 16, 45–49.
Bjone, S.J., Brown, W.Y. & Price, I.R. (2009). Maternal influence on grass eating in puppies. Journal of Veterinary Behavior, 4(2), 97–98. https://doi.org/10.1016/j.jveb.2008.10.003
Hart, B.L. (2008). Why do dogs and cats eat grass? Veterinary Medicine, 103, 648–649.
Kang, B.-T., Jung, D.-I., Yoo, J.-H. et al. (2007). A high fibre diet responsive case in a Poodle dog with long-term plant eating behavior. Journal of Veterinary Medical Science, 69, 779–782. https://doi.org/10.1292/jvms.69.779
McKenzie, S.J., Brown, W.Y. & Price, I.R. (2010). Reduction in grass eating behaviours in the domestic dog, Canis familiaris, in response to a mild gastrointestinal disturbance. Applied Animal Behaviour Science, 123, 51–55. https://doi.org/10.1016/j.applanim.2009.12.003
Sueda, K.L.C., Hart, B.L. & Cliff, K.D. (2008). Characterisation of plant eating in dogs. Applied Animal Behaviour Science, 111, 120–132. https://doi.org/10.1016/j.applanim.2007.05.018