Why Does My Dog Eat Grass?
It happens constantly, it looks purposeful, and it has been generating myths for decades. The most persistent one — that dogs eat grass to make themselves vomit — is not supported by the evidence. Here is what we actually know, and what to pay attention to.
Most grass eating in dogs is normal, frequent, and causes no harm. Research shows fewer than 25% of grass-eating episodes result in vomiting, which means the “dogs eat grass to be sick” explanation doesn’t hold up statistically. The most likely reasons are instinct, dietary fibre, taste and texture enjoyment, and — in a minority of cases — mild GI discomfort.
What the research actually shows
The most comprehensive study on grass eating in dogs — a 2008 survey of over 1,500 dog-owning households published in Applied Animal Behaviour Science — found that 79% of dogs ate plant material regularly. Of those, only 22% vomited after eating grass most of the time. Only 9% of owners reported their dog showing signs of illness before eating grass.
These numbers challenge the common assumption that grass eating is a deliberate emetic strategy. If it were, we would expect far higher rates of both pre-grass illness and post-grass vomiting. Instead, the data suggests grass eating is primarily a normal behaviour that occasionally — not reliably — results in vomiting.
The most plausible explanations
1. Ancestral behaviour and instinct
Wild canids regularly consume plant material — grass, berries, herbs — as part of their natural diet. Analysis of wolf scat shows plant material in roughly 11–47% of samples depending on the season. Dogs haven’t lost this instinct. Grass eating may simply be a retained ancestral behaviour that requires no further explanation than “they are wired to do this.”
2. Dietary fibre
Grass is a source of dietary fibre. Dogs who eat grass sometimes do so in correlation with low-fibre diets. Switching to a higher-fibre food or adding a fibre supplement sometimes reduces grass-eating frequency — suggesting that at least some grass eating is nutritionally motivated.
3. Taste and texture
Particularly in spring when grass is young, sweet, and tender, many dogs eat it with evident enjoyment and no distress whatsoever. The texture, moisture content, and flavour may simply be something dogs like. Not every behaviour needs a medical explanation.
4. Mild GI discomfort
A minority of grass-eating episodes appear to correlate with pre-existing nausea or GI discomfort. The dog may be using grass consumption — and the subsequent vomiting — as a mechanism to relieve discomfort. This is the grain of truth behind the myth, but it describes a minority of cases, not the typical scenario.
5. Boredom or under-stimulation
Some dogs eat grass as a default activity in an unstimulating environment — it’s something to do. Dogs who are under-exercised, under-stimulated, or spending long periods in a garden alone often eat more grass than dogs with adequate activity and engagement.
When grass eating is fine
- The dog eats grass calmly and deliberately, without distress
- The grass eating does not reliably precede or follow vomiting
- The dog is otherwise eating normally and behaving well
- The behaviour has been occurring for a long time without change
When grass eating warrants attention
- The behaviour is sudden and urgent — a dog who attacks grass frantically rather than grazing calmly may be experiencing acute GI distress
- Vomiting consistently follows — particularly if the vomit contains blood or the dog appears ill
- The grass is treated — herbicides, pesticides, fertilisers, and slug pellets on grass are toxic to dogs; know what has been applied to any grass your dog accesses
- Other symptoms are present — not eating, lethargy, diarrhoea alongside grass eating suggests GI disease rather than incidental grass consumption
- The frequency has significantly increased — a sudden change in any established behaviour pattern is worth noting
Should you stop your dog eating grass?
If the grass is untreated and the dog is healthy, there is generally no medical reason to prevent it. Management reasons — you’d rather not deal with the vomiting on the carpet — are valid, but they are preference reasons, not health reasons. If you want to reduce grass eating, providing more dietary fibre, increased exercise and enrichment, and ensuring the dog isn’t accessing treated lawns are the most effective approaches.