Is Black Walnut safe for cats and dogs?
| Species | Verdict |
|---|---|
| Cats | Safe |
| Dogs | Toxic |
Severity: Severe
Read the full first-aid guide: what to do if your pet ate something toxic
Black walnut (Juglans nigra) is a large native shade tree across the eastern and central United States, common on rural properties, wooded lots, and older suburban yards from the Northeast down through Texas and Florida, per NC State Extension's Plant Toolbox. It's less often deliberately planted close to a house today because its roots produce juglone, a compound that stunts nearby garden plants like tomatoes and azaleas, but mature trees are common enough that a dog sharing a yard with one will regularly encounter fallen nuts. Nuts develop inside a green-yellow husk and mature by October, then sit on the ground through fall and into winter as they dry, split open, and - if left there - start to mold.
That moldy, fallen-nut stage is where the real danger sits, and it involves two distinct things worth separating. First, ASPCA's plant database lists black walnut itself as toxic to dogs and toxic to horses, but explicitly non-toxic to cats; its stated toxic principle is 'unknown,' and the clinical picture it gives for dogs is specifically about moldy nuts and hulls - tremors, seizures, and incoordination from ingesting shavings. Second, and separately, the Merck Veterinary Manual documents a well-characterized condition called tremorgenic neuromycotoxicosis, in which mold - typically Penicillium crustosum - growing on walnuts (along with peanuts and other foods) produces tremorgenic mycotoxins such as penitrem A that disrupt neurotransmitter signaling and cause vomiting, tremors, ataxia, and seizures, sometimes within one to two hours of ingestion. Merck describes this for walnuts broadly rather than naming black walnut by species, but it is the same mold-driven mechanism ASPCA is describing for old black walnuts lying under a backyard tree - which is why the pile of aging nuts under the tree is the practical hazard, more than the fresh nut or the tree itself.
Because tremors and seizures from moldy nuts are a genuine neurologic emergency, a dog that has gotten into old walnuts on the ground and starts trembling, stumbling, or twitching needs immediate veterinary care - call ASPCA Animal Poison Control (888-426-4435) or Pet Poison Helpline (855-764-7661) right away. Raking up and disposing of fallen nuts before they have a chance to mold is the most practical prevention for a yard with a mature black walnut tree.
Facts and examples
- ASPCA lists black walnut as toxic to dogs and toxic to horses, and non-toxic to cats; toxic principle is listed as unknown, and clinical signs given for dogs are that moldy nuts/hulls can cause tremors and seizures, and that ingestion of shavings can cause incoordination. (source, verified 2026-07-28)
- The Merck Veterinary Manual describes tremorgenic neuromycotoxicosis in dogs caused by Penicillium mold (e.g. Penicillium crustosum) growing on walnuts and other foods, producing tremorgenic mycotoxins such as penitrem A that cause vomiting, tremors, ataxia, and seizures, with signs sometimes appearing within one to two hours. (source, verified 2026-07-28)
- NC State Extension's Plant Toolbox states black walnut is native to the eastern US west to Texas and south to Florida, that nuts develop in a husk and mature by October, and separately tags the species as toxic to dogs and horses but non-toxic to cats. (source, verified 2026-07-28)
Verdict re-verified against aspca.org, 2026-07-28 — confirmed unchanged. Source
This page is for general information only and is not veterinary advice, diagnosis, or treatment. If your pet is showing symptoms, or you think they ate or touched something dangerous, contact your veterinarian or a pet poison-control hotline immediately.
Last verified 2026-07-28