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

You let your dog out for a quick bathroom break, and instead of sniffing around, they start mowing the lawn like a small, furry goat. It is one of the most common questions dog owners ask vets: why do dogs eat grass, and should you stop it?

The popular answer is that dogs eat grass to make themselves throw up when they feel sick. The research tells a different story. Most grass-eating dogs are healthy, most do not vomit afterward, and the habit probably runs deeper than any one upset stomach.

This guide covers what the studies actually found, the most likely reasons your dog grazes, the real risks (which are mostly about what is on the grass), the signs that mean a vet visit, and practical ways to curb the habit. Where the rules differ, we cover both the US and Canada.

Why do dogs eat grass? The short answer

Dogs eat grass mainly because it is a normal, likely inherited behavior, and many simply seem to enjoy it. Boredom, an upset stomach or a craving for something to chew can play a part in some dogs. Nobody has proven one single cause, and different dogs probably graze for different reasons.

What vets agree on is this: occasional grass eating in a dog that is otherwise eating, playing and pooping normally is not, by itself, a reason to worry.

What the research says about dogs eating grass

Surprisingly few studies have looked at this closely, but the two best-known ones point the same way.

The largest is a 2008 study from the University of California, Davis, published in Applied Animal Behaviour Science by Sueda, Hart and Cliff. The team surveyed owners of dogs that had daily access to plants. Of 1,571 usable internet survey responses, 68% said their dogs ate plants daily or weekly. Grass was the most commonly eaten plant, named for 79% of dogs.

The key findings for owners:

• Few dogs looked sick first. Only about 8% to 9% of dogs frequently showed signs of illness before eating plants.
• Most did not vomit. Only 22% regularly vomited afterward.
• Younger dogs grazed more. They ate plants more often and were less likely to seem ill or vomit.
• Diet did not explain it. The researchers found no link between plant eating and diet type, sex, neuter status or breed group.

A smaller experiment by McKenzie, Brown and Price, published in the same journal in 2010, watched dogs offered fresh grass. Across 374 recorded grass-eating events, dogs vomited only twice. The dogs also ate less grass, not more, when a diet change gave them loose stools. The authors concluded that dogs did not seem to use grass to treat diarrhea, though they could not rule out other stomach issues.

Common claim	Evidence	What we know
Grass eating is normal in healthy dogs	Moderate	Large owner survey (UC Davis, 2008); consistent with vet guidance
Dogs eat grass to make themselves vomit	Limited	Only 22% vomited regularly in the survey; 2 vomits in 374 events in the 2010 experiment
Dogs eat grass because they lack fiber or nutrients	Limited	Diet type showed no link in the 2008 survey; no controlled trial proves it
Grass eating is inherited from wild ancestors	Moderate	Plant material shows up in wolf diets; leading researchers favor this theory
Boredom or anxiety drives it in some dogs	Limited	Widely reported by vets and behaviorists, but not well studied

6 likely reasons your dog eats grass

Here are the explanations for why dogs eat grass that have the most support, roughly from most to least common in a healthy adult dog.

1. It is an inherited behavior

Wild canids eat plants too. VCA Animal Hospitals notes that studies of wolf droppings have found grass in roughly 11% to 47% of samples. Benjamin Hart, a veterinary behaviorist on the UC Davis team, has suggested a possible reason: regular plant eating may have helped wild ancestors push intestinal worms through the gut. Modern dogs may keep the urge even though most now get routine parasite prevention.

2. They like the taste or texture

Some dogs are simply grazers. Many owners notice their dog gets choosier in spring, picking tender new shoots and ignoring dry or tough blades. If your dog nibbles calmly, chews the grass and then moves on, enjoyment is the most likely explanation.

3. Boredom or excess energy

A dog left alone in the yard has few things to do, and grass is always there. Young, high-energy dogs are the most likely to graze out of boredom. If the habit mostly happens when your dog is outside alone, more exercise and play are a good first step.

4. An upset stomach (sometimes)

The research above suggests this explains a minority of cases, not most. Still, the pattern matters. A dog that suddenly gulps grass urgently, barely chewing, while licking its lips or swallowing hard, may feel nauseous. That deserves attention, especially if it is new behavior.

5. Seeking fiber or something to chew

This theory is popular online, but the evidence is thin. The 2008 survey found no link between diet type and grass eating. A dog on a complete and balanced food does not need grass to meet its nutrient needs. If you suspect a diet issue, talk to your vet before adding supplements or switching food.

6. Pica: when it is more than grass

Pica means repeatedly eating things that are not food, such as dirt, rocks, fabric or plastic. Grass alone rarely counts. However, a dog that also eats soil, sticks, socks or poop should see a vet. Pica can be linked to medical problems, stress or compulsive behavior, and swallowed objects can cause blockages.

Why does my dog eat grass and throw up?

Your dog may throw up after eating grass because long blades irritate the stomach, or because it already felt queasy. But the research suggests vomiting is usually incidental to grass eating, not its purpose. Hart’s team summed it up: vomiting seems to happen alongside plant eating rather than being caused by it.

An occasional episode, where your dog brings up a wad of grass and then acts normal, is rarely a concern. Repeated vomiting is different, with or without grass. If your dog tends to vomit yellow foam on an empty stomach, the grass may be a side note. See our guide on why a dog throws up yellow bile in the morning for the feeding changes that often help.

Cleaning up is the other half of the job. If a grassy mess lands on the carpet, our guide to removing pet stains naturally covers vomit spots step by step.

Is eating grass bad for dogs? The real risks

Grass itself is not toxic to dogs. The risks come from what is on it, what grows next to it and how much your dog swallows.

Lawn chemicals

Herbicides, insecticides and fertilizers are the biggest concern. A 2013 Purdue University study in Science of the Total Environment tested urine from 25 dogs whose owners had treated their lawns. Researchers found lawn herbicides, including 2,4-D, in the dogs’ urine. Some dogs from untreated homes had them too, likely from neighboring lawns. The researchers advised letting products dry before pets go on the lawn and wiping dogs’ feet after contact.

Most fertilizer ingestions cause mild stomach upset, according to an ASPCA Animal Poison Control Center toxicologist writing in Today’s Veterinary Practice (2016). Products that contain bone meal, blood meal or insecticides are more worrying. “Weed and feed” products combine fertilizer and herbicide, so both ingredients matter.

Rules on lawn products differ by country:

• In the US, the Environmental Protection Agency (EPA) registers pesticides, and it is illegal to use one in a way that conflicts with its label. Read the label before letting your dog onto a newly treated lawn.
• In Canada, Health Canada registers pesticides under the Pest Control Products Act. Several provinces go further. Ontario, for example, has banned most cosmetic pesticide use on lawns and gardens since April 2009. Your neighborhood park or boulevard may still be treated for other reasons, so check local signs.

Toxic plants mixed in with grass

A dog that grazes may not stop at grass. The ASPCA’s toxic and non-toxic plants list includes over 1,000 entries. Several common garden plants, such as azaleas, oleander and sago palm, can cause serious poisoning in dogs. Sago palm seeds are especially dangerous and can cause liver failure. Check your yard and planters against the ASPCA list.

Intestinal parasites

Grass in parks and dog areas can be contaminated with droppings. The Companion Animal Parasite Council (CAPC) says roundworm eggs are hardy and can stay infective in soil for years. Some of these worms can also infect people, especially children. This is one reason CAPC recommends year-round parasite control and regular fecal testing. Ask your vet which plan suits your dog.

Grass awns and foxtails

Some wild grasses produce barbed seed heads, often called foxtails or grass awns. UC Davis veterinarians warn that their barbs only move one way, so they can work deeper into the nose, ears, mouth, skin or even the chest. Sudden sneezing, head shaking, pawing at the face or gagging after time in long grass needs a prompt vet check. These awns are most common in summer, once grasses dry out.

Large amounts

VCA notes that a large volume of grass can occasionally collect in the stomach and need surgical removal. This is rare, but it is another reason to curb nonstop grazing.

Normal grazing or a reason to call the vet?

Use this side-by-side as a quick guide. It is not a diagnosis, but it helps you decide whether to watch or call.

Usually normal	Worth a vet call
Calm nibbling, chewing the grass before swallowing	Sudden, frantic gulping of grass, especially if new
Has grazed on and off for years	Grass eating has recently increased a lot
Vomits grass once, then acts normal	Vomits repeatedly, or vomiting comes with other symptoms
Normal appetite, energy and stools	Diarrhea, lethargy, weight loss or a poor appetite
Eats only grass	Also eats dirt, rocks, fabric, sticks or poop
Untreated grass you know is safe	Ate grass treated with chemicals, or a plant you cannot identify

When to call your vet about grass eating

If you think your dog ate a toxic plant or a lawn product, call your vet or an animal poison hotline right away. In the US, that includes the ASPCA Animal Poison Control Center. The Pet Poison Helpline serves both the US and Canada. Both run 24/7, and a consultation fee may apply. Have the product label or a photo of the plant ready.

How to stop your dog from eating grass (or make it safer)

If your dog’s grazing is occasional and the grass is clean, you do not have to stop it. If you want to cut back, or your dog grazes on lawns you cannot vouch for, these steps help:

1. Teach “leave it.” Practice indoors with a treat first, then on walks. Reward your dog the moment it turns away from the grass.
2. Carry better options. A few small treats or a favorite toy make redirecting easier than pulling on the leash.
3. Add exercise and enrichment. Longer walks, fetch, sniff games and food puzzles reduce boredom grazing.
4. Avoid treated lawns. Watch for small lawn-care flags or signs, and steer clear of fresh treatments.
5. Wipe paws after walks. A damp cloth helps remove residues your dog might otherwise lick off later.
6. Make your own yard safe. Choose pet-safe lawn care, follow every label exactly and remove toxic plants.
7. Stay current on parasite control. Ask your vet about a year-round plan and regular fecal tests.
8. Do not punish grazing. Scolding can create anxiety, which may make the habit worse. Redirect instead.

A real-world example

Here is a hypothetical. Your two-year-old Border Collie mix grazes for a few minutes most mornings, chews slowly and then plays as usual. She has never vomited after grazing, and your yard is untreated. This is classic normal grazing. More morning exercise and a “leave it” cue are reasonable, but there is no urgency.

Now picture the same dog suddenly eating grass frantically, licking her lips and vomiting three times in an afternoon. That is a change in behavior plus repeated vomiting. Call your vet the same day.

The bottom line

So, why do dogs eat grass? For most dogs, it is a normal and probably inherited habit, and many simply like it. The research does not support the idea that dogs mainly eat grass to make themselves sick. The real risks are lawn chemicals, toxic plants, parasites and foxtails, not the grass itself. Keep your dog off treated lawns, stay on top of parasite control, and call your vet if grazing suddenly changes or comes with vomiting, diarrhea or lethargy.

For more practical, source-backed answers on digestion, food and behavior, browse our Dog Care section, including whether dogs can eat eggs safely.

How we researched this article

This guide draws on peer-reviewed studies in Applied Animal Behaviour Science and Science of the Total Environment, plus guidance from UC Davis, VCA Animal Hospitals, the ASPCA Animal Poison Control Center, CAPC, the US EPA, Health Canada and the Government of Ontario. It is general information, not veterinary advice. If your dog is unwell, contact your veterinarian.

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