There are more than 75 different varieties of hydrangeas, and each one contains poisons that, if consumed in high numbers by cats, can be harmful. The Bigleaf hydrangea (Hydrangea macrophylla), on the other hand, is the variety of hydrangea that is most hazardous to cats. This plant contains a chemical that, when taken in excessive doses by cats, can result in vomiting, diarrhea, and lethargy. Additionally, the Bigleaf hydrangea’s blooms have a higher toxic content than the plant’s leaves or stems do.
While some hydrangea varieties could be more hazardous than others, any plant can be harmful to cats if consumed in sufficient amounts. Consult a veterinarian right away if you think your cat may have consumed any plant material, including hydrangeas.