Safety verdict
Consulted references classify the plant as toxic or irritating for that pet type.
Pet ingestion lookup
My cat 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, lethargy, and potential abdominal pain.
Escalation note
Ingestion can lead to gastrointestinal upset. Please contact your veterinarian or a pet poison control center if you suspect your cat has consumed any part of this plant.
What to watch for
Most common: vomiting, diarrhea, and depression — your cat retreats and won't engage. Possible: drooling, abdominal discomfort. Rare: signs of cyanide effect, such as bright red gums, panting, or weakness.
Time window
Pet Poison Helpline notes signs of cyanide effect can appear within 15–20 minutes of a large ingestion. The far more common GI upset is usually self-limiting once the plant has cleared the stomach.
When to call the vet
Call immediately if your cat shows weakness, panting, or bright red gums (possible cyanide effect). For mild GI signs, call if vomiting or diarrhea continues past a few hours, especially in kittens or seniors who can dehydrate quickly.
What this means for your cat
Hydrangeas contain cyanogenic glycosides, which sounds frightening but in practice almost always cause stomach upset rather than cyanide poisoning. Cats are more sensitive than dogs because of their smaller body size, but full-blown cyanide signs are rare. Expect vomiting and a quiet, withdrawn cat in most cases.
Sources: ASPCA, Pet Poison Helpline.
Poison-control resources
This page summarizes source-bound plant-safety information and is not veterinary advice.