Why Do Dogs Eat Grass? What Research Really Shows

A Poodle walking through tall grass in a dog park — Photo: Bobscola (talk · contribs), public domain, via Wikimedia Commons

You’re halfway through a nice walk when your dog suddenly stops, plants their feet, and starts chewing on a patch of grass like it’s the best salad in town. You tug the leash. They take one more bite.

Many of us grew up hearing that dogs only eat grass when they feel sick and need to throw up. It’s one of those things everyone seems to “know.” But when researchers actually asked owners, the answer turned out to be a lot less dramatic, and a lot more interesting.

The big survey that surprised everyone

At the University of California, Davis, veterinary behaviorist Benjamin Hart and his colleagues set out to find out how common grass eating really is and whether it has much to do with illness. Their work, led by Karen Sueda and published in Applied Animal Behaviour Science in 2008, started with a small pilot survey of 25 veterinary students. All of them said their dogs ate grass, and none had seen their dog look ill beforehand.

Then the team went bigger. An online survey gathered usable answers from 1,571 dog owners. In that group, 68% said their dogs ate plants daily or weekly. Only 9% said their dog frequently seemed ill before eating plants, and only 22% said their dog frequently vomited afterward.

The researchers’ conclusion was refreshingly simple. Grass eating “commonly occurs among all breed groups of domestic dogs and appears to be a normal behaviour unassociated with illness, vomiting or dietary deficiency.”

💡 Did you know? The UC Davis team found that younger dogs ate plants more often, and they were less likely to seem sick beforehand or to vomit afterward. So frequent grazing in a young dog doesn’t necessarily point to an upset stomach.

So if your dog throws up after a big grass snack, it can happen. It’s just not the main story for most dogs.

Wolves eat grass, too

If grass eating were only a quirk of pampered pets, we wouldn’t expect to see it in wild canines. But we do.

According to VCA Animal Hospitals, stool samples show that 11% to 47% of wolves eat grass. In the UC Davis paper, the authors also cite a study in which plant matter showed up in about 74% of summer scat samples from gray wolves reintroduced to Yellowstone National Park.

That points to something old and built-in, rather than a new habit our dogs picked up on suburban lawns.

So why would a wolf eat grass?

This is where the story gets a little gross, and a lot more fascinating.

The UC Davis researchers describe how, back in 1944, a researcher named Murie observed blades of grass wrapped around intestinal worms in wolf scats. He suggested that grass might have a scouring effect, helping to sweep worms out of the gut.

Hart built on that idea. Writing for dvm360, he proposed that plant eating may have served an ancient purpose: undigested plant material can speed things along in the intestines and help carry parasites out. He points to a similar behavior in wild chimpanzees, who swallow whole leaves that pass through the gut intact, sometimes along with intestinal worms.

Many pet dogs today are on regular parasite prevention, but the instinct may still be there, quietly suggesting that a mouthful of grass is a good idea.

Two Borzois playing on a lawn — Photo: ROVER_JP / CC BY 2.0, via Wikimedia Commons

Hunger, fiber, and plain old boredom

There are a few other ideas, and they may all play a part.

Hunger and timing. In a 2007 study from the University of New England in Australia, Samantha Bjone and colleagues gave 12 dogs access to grass three times a day for six days. The dogs spent more time eating grass before their kibble meal than after, and grazing tapered off as the day went on. That suggests an empty stomach may make grass more tempting.

Fiber. VCA notes that grass provides roughage, which helps with digestion and the passing of stool. A remarkable case from Korea supports this idea. In 2007, veterinarians at Konkuk University described an 11-year-old Miniature Poodle who had been eating plants on walks and vomiting afterward for seven years. Medical exams found nothing abnormal. When the dog was switched to a high-fiber diet, the plant eating and vomiting stopped within three days and hadn’t returned 13 months later. The authors wrote that the case “shows a possibility that deficient diet, especially fiber, relates to the plant eating behavior of a dog.” It’s one dog, so it can’t prove anything about all dogs, but it’s a fascinating clue.

Boredom or anxiety. VCA says some dogs eat grass when they’re bored, lonely, or anxious, a bit like a person nervously biting their nails. The Korean pet site BeMyPet suggests that when there’s no health reason behind it, more active play on walks, like fetch or a frisbee game, may help.

They might simply like it. The AKC lists taste and texture among the possible reasons, so for some dogs, grass may just be a snack they enjoy.

The real risks are on the grass, not in it

For most dogs, the grass itself isn’t the problem. What’s sprayed on it, growing next to it, or left on top of it can be.

Lawn chemicals are a big one. The AKC and PetMD both warn that grass treated with herbicides or pesticides can be toxic. PetMD lists excessive drooling, nausea, vomiting, diarrhea, and a decreased appetite as possible signs, and advises bringing your dog to a vet right away, along with the product label if you have it. BeMyPet makes the same point: the grass itself isn’t the danger, but the herbicides and insecticides sprayed on it can be dangerous.

Fertilizer is another one. The ASPCA notes that it can be very appealing to curious dogs. If eaten, it can cause vomiting, diarrhea, and weakness or stiffness in the hind legs. Keep your dog out of the area while you’re using fertilizers or insecticides, and follow every label instruction.

A dog who grazes freely may not stop at grass, either. The ASPCA warns that sago palms are highly toxic to dogs and can lead to liver failure, and that tulip, hyacinth, and daffodil bulbs can cause vomiting and diarrhea.

Then there’s what other animals leave behind. According to the AKC and VCA, grass that other animals have used as a bathroom can carry intestinal parasites such as roundworms and hookworms, and PetMD adds parvovirus to that list. Keeping your dog’s parasite prevention up to date helps. PetMD also notes that eating a large amount of grass can occasionally cause an intestinal blockage, especially if it’s mixed with non-food items.

💡 Good to know: In Korean, the common foxtail weed is called gangaji-pul (강아지풀), literally “puppy grass,” because its fuzzy spike looks like a puppy’s tail. Cute name, but Namuwiki notes that wild plants like it often carry ticks, so it’s not something to let your dog chew on.

When to call your vet

Occasional grass nibbling in a healthy, happy dog is usually nothing to worry about. A change in the pattern deserves a closer look.

The AKC suggests checking in with your vet if your dog:

eats grass frequently or excessively
vomits, has diarrhea, or is losing weight
loses interest in food
has bloody stool or seems unusually tired
keeps licking their lips

VCA notes that signs of stomach discomfort can point to medical problems such as gastric reflux, inflammatory bowel disease, or pancreatitis. Your vet may suggest a fecal test or bloodwork to get a clearer picture.

⚠️ Please don’t wait. If your dog may have eaten grass or plants treated with pesticides, fertilizer, or other chemicals, or a plant you know is toxic, call your vet or an emergency clinic right away. In the U.S., the ASPCA Animal Poison Control Center is available 24/7 at (888) 426-4435 (a consultation fee may apply).

Angel Jake Note 🐾

If you’ve ever pulled your dog away from the grass in a panic, thinking they must be sick, you’re in very good company. It’s such a common belief, and it comes from a caring place.

The science gives us a gentler way to see it. That little grazing session may be an old instinct, a hungry tummy, a need for a bit more fiber, or just a fun thing to do on a slow walk. Let them enjoy a nibble on clean grass you trust, keep them away from treated lawns and unknown plants, and pay attention if anything about the habit suddenly changes.

Medical Disclaimer

I’m not a vet, and nothing here replaces a real exam. If something about your dog feels off, please trust that feeling and call your veterinarian.