Safety verdict
Consulted references classify the plant as toxic or irritating for that pet type.
Pet ingestion lookup
My dog ate Smooth Hydrangea - what should I do?
Hydrangea arborescens
Potentially toxic
Contact your veterinarian or an animal poison-control resource now, especially if any amount was chewed or swallowed.
Verified against ASPCA/provenance audit 2026-05-06 on May 6, 2026.
Signs to watch for
Vomiting, diarrhea, increased heart rate, and potential depression.
Escalation note
While usually mild, ingestion can cause significant digestive irritation. Always consult a veterinarian if your dog shows signs of illness after exposure.
What to watch for
Most common: vomiting, diarrhea, and depression (lethargy, withdrawal). Possible: drooling, increased heart rate, mild abdominal pain. Rare: bright red gums, panting, or collapse — signs of true cyanide effect after a heavy ingestion.
Time window
Pet Poison Helpline: cyanide-type signs can appear within 15–20 minutes of a large ingestion. The much more common GI upset is typically self-limiting and resolves once the stomach clears.
When to call the vet
Call immediately if you see weakness, bright red gums, panting, or rapid breathing — those can signal cyanide effect after a large dose. For mild GI signs, call if vomiting or diarrhea persists past a few hours or your dog can't keep water down.
What this means for your dog
Hydrangea arborescens is on the ASPCA toxic list because the leaves and flower buds contain cyanogenic glycosides. In practice, dogs that chew hydrangea almost always end up with vomiting and diarrhea — not full cyanide poisoning, which would require a much larger ingestion.
Sources: ASPCA, Pet Poison Helpline.
Source references
Poison-control resources
This page summarizes source-bound plant-safety information and is not veterinary advice.