Are Hydrangeas Poisonous to Animals?

A Garden Favorite

• There are 23 recognized species of hydrangea (Hydrangea spp.) and they can produce flowers ranging from white or pink to mauve or purple. Hardy in U.S. Department of Agriculture plant hardiness zones 3 through 9, hydrangeas can grow from 3 1/2 feet to 10 feet in height and come in many varieties, including climbing species, smooth and tree varieties, oakleaf hydrangeas and big leaf hydrangeas.

Toxic Substances in Hydrangeas

• The toxic principal in hydrangeas is called hydrangin, a cyanogenic glycoside. If ingested in large quantities, this substance can be toxic to dogs, cats and horses. All parts of the plant are potentially hazardous, but the greatest concentration of the cyanogenic glycosides exist in the leaves, bark and flower buds. All species of hydrangea are potentially toxic.

Signs of Poisoning

• Animals generally will not eat this shrub, however, if an animal does ingest the leaves or flowers of a hydrangea bush, it may show signs of toxicity, which include vomiting, depression, bloody diarrhea and painful gastroenteritis. Cyanide intoxication or severe poisoning is rare, however, and usually causes more of a gastrointestinal disturbance.

If Poisoning Occurs

• If your pet has inadvertently eaten part of a hydrangea shrub, seek help from your veterinarian immediately, even if the animal is not showing any symptoms yet. The sooner that your pet can be treated, the better, in order to minimize the potential problems. Another option is to call the ASPCA Poison Control Center at (888) 426-4435.