Common Toxic Garden Plants
Daffodil

Daffodils are a strikingly colorful flower. This can sometimes bring them much attention not from just onlooking adults but children as well. Since kids are more drawn to colorful objects, they may have a higher chance of just grabbing the flower and eating it. Adults have also been known to accidentally grab daffodil bulbs instead of onions.
Why are these mistakes so dangerous? Daffodils contain lycorine, which can induce nausea, vomiting, and diarrhea. It also contains oxalates which can cause swelling and pain. The symptoms can be worse in animals, because if your pets eat daffodils they may experience drowsiness, low blood pressure or even liver damage.
Make sure to call poison control when these symptoms set in. The vomiting and diarrhea have been known to go away after 3 hours, but it is better to be safe than sorry. Ingesting liquids to keep hydration up can be important. If the patient is having difficulty breathing, seek medical attention immediately.
Hydrangea

Hydrangeas are unique, with their soft blue and pink flowers. They are a great addition to any garden, but should not be snacked on—not that you would want to. Hydrangeas can be especially nasty because they contain compounds known as glycosides. These will release hydrogen cyanide into the bloodstream when consumed. This will block your body’s ability to uptake oxygen to the cells in your body.
As you can imagine this is very serious. People experiencing this type of poisoning will tremble, gasp for air, have a hard time getting up, and experience impaired coordination. Pets’ symptoms can be slightly different since they will show “signs of excitement and generalized muscle spasms, staggering gait, and vomiting, followed by severe clonic convulsions and respiratory distress,” according to Science Direct.
The way to combat this kind of poisoning is through getting IVs from the vet or doctor. It is important to contact your medical professional immediately since the symptoms can be fatal within minutes or hours.
Rhododendrons

Rhododendron, the state flower of Washington, is also toxic. The multitudinous, pink flowers can be quite dangerous. All parts of this plant are toxic, the leaves and seeds more so than the flowers. However, even the nectar of the flower is toxic and in the Mediterranean, where rhododendrons grow in more dense quantities, the honey from bees who gather rhododendron nectar can be poisonous.
Normally kids and pets do not eat enough to experience the full poisoning effect. However, just eating two leaves is enough to be considered dangerous. The grayanotoxin glycosides within the rhododendron can cause vomiting, diarrhea and irregular heartbeats. Things can get very serious when too much rhododendron is consumed and can lead to necessary medical intervention.
Start by calling poison control first if you suspect anyone has been munching on rhododendrons. The experts there will be able to help guide you through the necessary processes to cure your loved one.
Rhubarb

Yummy rhubarb has a nasty side to it. While the stems are used in many recipes, including for rhubarb strawberry pie, the leaves are toxic. They contain oxalic acid which is known to blister the mouth, cause nausea, vomiting, diarrhea and kidney stones. The leaves are known to be more toxic to pets than humans, but in either case, it is important to contact poison control immediately to figure out necessary steps to cure the patient.