Reference
Are Hydrangeas Toxic to Dogs and Cats?
The short answer
Yes, hydrangeas are toxic to pets. The ASPCA lists hydrangea (Hydrangea arborescens) as toxic to dogs, cats, and horses, with the toxic principle a cyanogenic glycoside, and the main clinical signs being vomiting, depression, and diarrhea.
In reality, serious cyanide poisoning from hydrangea is uncommon; the usual concern when a pet chews leaves, flowers, or buds is a bout of stomach upset. Even so, if your pet eats a large amount or shows more than mild signs, contact your veterinarian or the ASPCA Animal Poison Control Center at (888-426-4435).
What the toxin is
The ASPCA identifies the toxic principle in hydrangea as a cyanogenic glycoside - a compound that can, in theory, release cyanide as it is broken down. This is why hydrangea appears on toxic-plant lists for dogs, cats, and horses.
In practice, the amount a pet would need to eat to produce true cyanide poisoning is large, and such severe reactions are uncommon. The everyday risk is gastrointestinal, not a cyanide crisis, but hydrangea is still correctly classified as toxic and not a plant pets should be grazing on.
Signs to watch for
The ASPCA lists the clinical signs as vomiting, depression, and diarrhea. These typically follow a pet chewing leaves, flower heads, or buds, and are usually self-limiting for a small nibble.
Watch for signs that go beyond mild stomach upset - repeated vomiting, marked lethargy, or any difficulty breathing - and treat a large ingestion more seriously than a single mouthful.
What to do
If your dog or cat eats a significant amount of hydrangea, or shows more than brief, mild signs, contact your veterinarian or the ASPCA Animal Poison Control Center at (888-426-4435). Note the plant and roughly how much was eaten.
For pet households that want to plant confidently, checking each species against an authoritative database is the reliable approach - see our page on how to check whether a plant is pet-safe.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- ASPCA - Toxic and Non-Toxic Plants: Hydrangea — Lists hydrangea (Hydrangea arborescens) as toxic to dogs, cats, and horses, toxic principle cyanogenic glycoside, with clinical signs of vomiting, depression, and diarrhea.