Dogs eat grass for several reasons including instinctive grazing behavior, fiber supplementation, and in some cases nausea relief — but contrary to popular belief, grass eating is rarely a sign of illness. A peer-reviewed study found that 79 percent of dogs eat plants regularly, yet only 9 percent showed signs of being ill before eating grass, and fewer than a quarter vomited afterward. The behavior is normal for most dogs and does not require intervention unless it becomes sudden, compulsive, or accompanied by other symptoms.
How Common Is Grass Eating in Dogs?
Grass eating is one of the most frequently reported unusual behaviors in domestic dogs, and it is far more common than most owners realize. A 2008 study by Sueda, Hart, and Cliff published in Applied Animal Behaviour Science surveyed owners of 1,571 dogs and found that 68 percent reported their dogs ate plants on a daily or weekly basis. Across all plant-eating dogs, grass was by far the most commonly consumed plant type.
Importantly, the study found no meaningful correlation between grass eating and subsequent vomiting. Only 22 percent of dogs that ate grass vomited afterward, and only 9 percent of dogs showed signs of illness before eating grass. These findings challenge the deeply held folk belief that dogs eat grass specifically to induce vomiting when they feel sick.
"Plant eating is common in wild canids and is likely a normal behavior that has been carried over into the domestic dog. The low proportion of dogs showing prior illness or vomiting after grass eating does not support the hypothesis that plant eating is primarily related to illness." — Sueda, Hart, and Cliff, Applied Animal Behaviour Science, 2008
Reason 1: Instinct From Wild Ancestors
The most evolutionary explanation is that grass eating is a behavioral relic of ancestral canids. Wolves and other wild canids regularly consume the stomach contents of their herbivore prey, including pre-digested plant material and grass. This consumption provides fiber, micronutrients, and possibly beneficial gut bacteria derived from the prey's digestive system.
Domestic dogs descended from wolves retain many ancestral behavioral tendencies, particularly around feeding. From this perspective, grass nibbling is no different from the instinct to bury food, circle before lying down, or sniff intensively before eating — behaviors with clear ancestral function even when the original context no longer applies.
Support for this hypothesis comes from studies of captive wolves and free-ranging dogs, which show regular plant consumption in the absence of any illness or nutritional deficiency.
Reason 2: Fiber Supplementation
Many veterinary nutritionists believe that grass eating is a self-regulatory behavior through which dogs supplement dietary fiber. Dogs on low-fiber diets appear to eat grass more frequently than those on high-fiber diets, and some dogs reduce their grass consumption when transitioned to diets with higher fiber content.
Fiber influences gastrointestinal motility, promotes healthy stool formation, and supports populations of beneficial gut bacteria. Dogs that consistently eat grass despite having access to it may benefit from a dietary fiber increase through vegetables, legumes, or a high-fiber commercial food formulation.
Notably, the relationship between grass eating and diet is not universal — many dogs on high-quality, high-fiber diets still eat grass regularly, suggesting that dietary supplementation is one of several motivations operating simultaneously.
Reason 3: Nausea Relief and Vomiting Induction
Although the Sueda study showed that vomiting after grass eating is less common than popularly believed, a subset of dogs do appear to use grass strategically when nauseous. The distinction may relate to how the grass is consumed: dogs that gulp large quantities rapidly and repeatedly swallow without chewing may be attempting to trigger the gag reflex, while dogs that leisurely graze and chew individual blades appear to be grazing without any illness motive.
Some research suggests that certain grass compounds have gastroprotective properties. Wheatgrass in particular contains chlorophyll, antioxidants, and trace minerals that have demonstrated anti-inflammatory and antacid properties in laboratory settings, though direct evidence in dogs remains limited.
If a dog that rarely eats grass suddenly begins consuming large amounts and regularly vomits afterward, this pattern warrants veterinary evaluation to rule out underlying gastrointestinal conditions including inflammatory bowel disease, gastric reflux, or foreign body obstruction.
Reason 4: Boredom and Grazing Behavior
Dogs that spend long periods outdoors without enrichment or engagement often develop habitual grazing behaviors that have no medical or nutritional basis. The repetitive oral activity of grazing is self-soothing for some dogs, similar to how some dogs chew non-food items when understimulated.
Owners who increase exercise, play, and training engagement often report a reduction in habitual grass eating. Providing appropriate chew toys, puzzle feeders, and social interaction gives dogs alternative outlets for oral and exploratory behavior.
This boredom-related grazing is more common in energetic breeds with high cognitive needs — Border Collies, Jack Russell Terriers, Australian Shepherds — that become restless when under-stimulated.
Reason 5: It Simply Tastes Good
Dogs have taste preferences, and many simply find certain grasses and plants palatable. Young, tender grass blades have a mild sweetness from chlorophyll and simple sugars that some dogs find appealing. Dogs commonly graze selectively, preferring certain grass species and ignoring others, behavior inconsistent with a strictly medicinal motivation.
Seasonal patterns support this interpretation: many owners report their dogs eat more grass in spring when new growth is especially tender and flavorful, and less in late summer when grass becomes tough and bitter.
When to Be Concerned About Grass Eating
| Grass Eating Pattern | Likely Cause | Action Needed |
|---|---|---|
| Occasional nibbling of grass blades | Normal grazing / instinct | None required |
| Frequent grazing during walks | Fiber seeking / habit | Consider high-fiber diet |
| Gulping large amounts rapidly | Possible nausea | Monitor; vet if persistent |
| Vomiting after grass eating (>50% of occasions) | Gastrointestinal issue | Veterinary evaluation |
| Sudden onset of heavy grass eating | Dietary change, illness, stress | Veterinary evaluation |
| Eating non-grass plants including toxic species | PICA / behavioral | Prevent access; vet consult |
| Accompanied by weight loss, appetite change | Underlying disease | Urgent veterinary evaluation |
Grass Eating vs. Eating Other Plants (PICA)
PICA is the compulsive consumption of non-food items, and while occasional grass eating is normal, compulsive consumption of soil, rocks, fabric, wood, or plants other than grass may indicate PICA. PICA can reflect nutritional deficiencies, gastrointestinal disease, neurological conditions, or anxiety disorders.
Of particular concern is consumption of ornamental and garden plants, many of which are toxic to dogs. The ASPCA Animal Poison Control Center lists over 400 plants toxic to dogs, including common garden species such as azalea, rhododendron, sago palm, oleander, and foxglove.
"Toxicity from plant ingestion is one of the most common reasons for calls to the ASPCA Animal Poison Control Center. Owners should know which plants in their yard and home are toxic to dogs and prevent unsupervised access to those areas." — ASPCA Animal Poison Control Center, 2023
Does Grass Carry Risks for Dogs?
Grass itself is not toxic to dogs. However, grass that has been treated with pesticides, herbicides, or fertilizers poses a genuine risk. Chemical exposures from treated lawns have been associated with gastrointestinal upset, neurological symptoms, and in severe cases, organ damage depending on the compound and quantity consumed.
Dogs that graze in areas that may have been treated should be observed after returning indoors. Signs of pesticide or herbicide toxicity include excessive salivation, vomiting, diarrhea, muscle tremors, or lethargy. If any of these signs appear following grass eating, veterinary care should be sought promptly and the owner should bring information about any chemicals recently applied to the lawn.
Intestinal parasites (roundworms, hookworms, whipworms) are transmitted through contaminated soil and can be ingested during grass eating. Dogs that graze regularly should be maintained on a veterinarian-recommended parasite prevention protocol.
Common Plants Dogs Eat and Their Safety
| Plant | Toxicity to Dogs | Notes |
|---|---|---|
| Lawn grass (most species) | Non-toxic | Safe unless treated with chemicals |
| Wheatgrass / oat grass | Non-toxic | Sometimes grown indoors as dog treat |
| Dandelion | Non-toxic | Mild diuretic; occasional eating safe |
| Clover | Generally non-toxic | Large quantities may cause bloating |
| Buttercup | Mildly toxic | GI irritant; avoid access |
| Foxglove | Highly toxic | Cardiac glycosides; emergency |
| Sago Palm | Extremely toxic | Liver failure; fatal in small amounts |
| Azalea / Rhododendron | Highly toxic | Cardiac and neurological effects |
What to Do If Your Dog Eats a Lot of Grass
For dogs that graze occasionally without vomiting or illness signs, no intervention is necessary beyond ensuring the grass is pesticide-free and maintaining routine parasite prevention. For dogs that seem compelled to eat grass, especially if vomiting follows, a trial of high-fiber diet supplementation is a reasonable first step.
Adding vegetables such as pumpkin, green beans, or carrots to the diet increases fiber intake in a controlled way. Some veterinarians recommend cat grass or wheatgrass grown indoors as a safe, pesticide-free alternative for dogs that graze habitually.
For further reading on related dog behavior and health topics, see Signs of a Healthy Dog, Why Do Dogs Lick People?, How Long Do Dogs Live?, How to Train a Puppy, and Why Do Dogs Howl?.
References
Sueda, K. L. C., Hart, B. L., & Cliff, K. D. (2008). Characterisation of plant eating in dogs. Applied Animal Behaviour Science, 111(1-2), 120-132. https://doi.org/10.1016/j.applanim.2007.05.018
Hart, B. L. (2008). Why do dogs and cats eat grass? Veterinary Medicine, 103(12), 648-649.
American Society for the Prevention of Cruelty to Animals. (2023). Toxic and non-toxic plants for dogs. https://www.aspca.org/pet-care/animal-poison-control/toxic-and-non-toxic-plants
Bjone, S. J., Brown, W. Y., & Price, I. R. (2007). Grass eating patterns in the domestic dog, Canis lupus familiaris. Recent Advances in Animal Nutrition in Australia, 16, 45-49.
Mech, L. D., & Boitani, L. (Eds.). (2003). Wolves: Behavior, Ecology, and Conservation. University of Chicago Press.
Frequently Asked Questions
Why do dogs eat grass?
Dogs eat grass for multiple reasons: instinct from wild ancestors, fiber supplementation, occasional nausea relief, boredom, and because some grass is palatable. Most grass eating is normal and not a sign of illness.
Should I stop my dog from eating grass?
Occasional grass grazing is generally safe and normal. You should prevent grass eating only if the lawn has been treated with chemicals, if your dog is eating non-grass toxic plants, or if vomiting consistently follows grass eating.
Is grass bad for dogs?
Plain, untreated grass is not toxic to dogs. The main risks are chemical contamination (pesticides, herbicides) and intestinal parasite transmission from contaminated soil.
Do dogs eat grass when their stomach hurts?
Some dogs do eat grass when nauseous, typically gulping large quantities rapidly. However, research shows most grass eating (91%) occurs without any prior signs of illness.
How can I reduce my dog's grass eating?
For dogs that seem to seek fiber, try adding high-fiber vegetables (pumpkin, green beans) to their diet. For boredom-related grazers, increasing exercise and mental enrichment reduces the behavior.
What plants are dangerous for dogs to eat?
Many ornamental plants are toxic including azalea, rhododendron, sago palm, oleander, foxglove, and buttercup. The ASPCA Animal Poison Control Center lists over 400 plants toxic to dogs.