Why Do Dogs Eat Grass? What the Research Says, and When to Worry

Dogs eat grass mainly because they like it, and it is rarely a sign that anything is wrong. The largest study of the habit found that most grass-eating dogs were not ill beforehand and did not vomit afterwards.

What matters is the rest of the picture. A dog who grazes on walks and carries on as normal is fine. A dog who is suddenly gulping grass, vomiting repeatedly or going off their food needs a vet. Here is how to tell which one you have.

What the Research Actually Found

The study most vets point to is a survey by Sueda, Hart and Cliff at the University of California, Davis, published in Applied Animal Behaviour Science in 2008. They analysed 1,571 questionnaires from dog owners.

• 68% of the dogs ate plants daily or weekly.
• Grass was the plant most often eaten, by 79% of them.
• Only 9% regularly seemed unwell before eating plants.
• Only 22% regularly vomited afterwards.
• Younger dogs ate plants more often, and were less likely to seem ill first or to vomit after.

The researchers concluded that plant eating is normal behaviour in dogs. Their suggestion is that it is an inherited habit: wild dogs and wolves eat grass too, and one theory is that it once helped them move intestinal worms through the gut. That part is a theory. The finding that most grass eaters are healthy is the solid bit.

UK charities say the same. PDSA calls it a common misconception that dogs eat grass because they are about to be sick, and Blue Cross says the most likely reason is that it tastes nice, especially fresh green grass in spring and summer.

Other Reasons Dogs Graze

Boredom. Blue Cross notes that some dogs graze because they have little else to do. If your dog mostly eats grass while hanging about in the garden, more walks, sniffing games and food puzzles often cut it back.

Habit and taste. Some dogs simply go for particular grasses, like long, soft blades at the edge of a path.

A missing nutrient? It is a popular idea, but there is no good evidence for it. Blue Cross says the belief that grass eating points to a nutritional gap has not been proven.

Normal, or See a Vet?

What you see	What it probably means
Nibbles grass on walks, otherwise bright and eating well	Normal
Occasionally sick with grass in it, fine straight after	Usually normal, keep an eye on it
Suddenly eating grass frantically, far more than usual	Worth a call to your vet, especially with other signs
Eating grass but not their normal food	See your vet
Eating grass and vomiting repeatedly over a few hours	See your vet today
Grass eating plus weight loss, diarrhoea or low energy	Book an appointment, something else is going on

See a vet today if:

• Your dog is vomiting repeatedly, or cannot keep water down.
• There is blood in the vomit.
• Your dog is retching without bringing anything up, or has a swollen, tight belly. PDSA lists this as a possible sign of a twisted stomach, which is a life-threatening emergency.
• They seem flat, weak or in pain, or will not eat.
• You think they have eaten a toxic plant or treated grass (see below).

Out of hours, Vets Now runs emergency clinics across the UK. Our dog first aid guide covers what to do on the way.

When Grass Eating Becomes Risky

The grass itself is not the problem. What is on it, or growing near it, can be.

Sprays, feeds and pellets

Weedkillers, lawn feeds and slug pellets can all be harmful. Dogs Trust advises speaking to your vet as soon as possible if your dog has come into contact with slug pellets, weedkillers or bonemeal fertiliser. Keep your dog off lawns that have just been treated, including yours, and follow the label on any product you use.

Toxic plants in UK gardens

A dog grazing along a border can end up chewing more than grass. Dogs Trust's list of plants that can poison dogs includes several very common ones:

• Yew. Found in hedges, gardens and churchyards. The ASPCA lists tremors, breathing difficulty, seizures and sudden heart failure among the effects. Treat any chewing as an emergency.
• Foxgloves. Common in gardens and woodland edges, and also affect the heart.
• Daffodils, especially the bulbs. A dog digging in a bed in autumn or winter can find them.
• Rhododendron, laurel, ivy and hydrangea, among others.

If your dog has chewed any of these, ring your vet straight away rather than waiting for symptoms. If you cannot get hold of a vet, Animal PoisonLine (01202 509000) is the 24-hour service run by the Veterinary Poisons Information Service.

Lungworm

This is the risk most owners have never heard of. PDSA explains that dogs catch lungworm by eating infected slugs and snails, which often happens by accident while they eat grass or drink from puddles. Blue Cross points out that most standard worming treatments from pet shops do not cover lungworm, so ask your vet whether your dog's does.

Grass seeds

In summer, the arrow-shaped seeds on long grass can lodge in paws, ears, eyes and noses, and occasionally get swallowed or inhaled. PDSA's guide to grass seeds covers the signs. Sudden sneezing, head shaking or licking at one paw after a walk through long grass is the usual clue.

Should You Stop It?

For a healthy dog nibbling untreated grass, no. It is normal and there is no evidence it does harm. What helps is steering where they graze:

• Keep them off lawns and verges you know have been sprayed.
• Know which toxic plants are in your garden, and fence off or remove the worst, particularly yew.
• Keep lungworm cover up to date.
• If it looks like boredom, give them something better to do.

If the habit changes suddenly, or comes with vomiting, diarrhoea, weight loss or a change in appetite, that is a vet visit. The grass is rarely the cause, but it can be a sign that your dog's stomach is not right. If your dog is also drinking more than usual, our guide to why dogs drink a lot of water is worth a read before the appointment.

Floofers is not a veterinary practice and nothing here is a diagnosis. If your dog is vomiting repeatedly, seems unwell or may have eaten something toxic, ring your vet.