Hogwarts of the Harry Potter films is set in Alnwick Castle, which has some beautiful gardens, one of which is carefully gated because it is home to 100 or so poisonous plant varieties.
Among the plants are coca, foxglove, nightshade, hemlock, henbane, giant hogweed and mandrake. Often the difference between helpmate and killer, remedy and poison is dose. Foxglove, for example, is beautiful and the source of digitalis an important heart medicine, too much foxglove/digitalis can kill.
Alnwick Castle’s Poison Garden came to be in 1996 after Jane Percy became the Duchess of Northumberland. A story in Smithsonian magazine tells the tale:
“The duchess thought she might want to include an apothecary garden, but a trip to Italy set her on a slightly different course. After visiting the infamous Medici poison garden, the duchess became enthralled with the idea of creating a garden of plants that could kill instead of heal.”
So that is just what she did.
"What’s extraordinary about the plants is that it’s the most common ones that people don’t know are killers," the duchess says. Visitors are often surprised to learn that the laurel hedge, nearly ubiquitous in English gardens, can be highly toxic. But some visitors have had experience with laurel's sinister side—the duchess has heard a few talk about how, after loading up their cars with pruned laurel leaves to take to the dump, drivers have fallen asleep behind the wheel of their car from the toxic fumes the branches emit.”
My daughter once grew Angel’s Trumpet, the version called Datura, in her California garden along with poppies and other pretty flowers.
She learned its story when a neighbor stole some flowers, and then the seed pods.
One plant on display is Brugmansia, or angel's trumpet, a member of the Solanaceae family (which includes other plants in the deadly nightshade family). By the way, eggplant, potatoes and tomatoes, are also in the nightshade family.
In the article Percy says that the plant grows in the wild in South America. "It's an amazing aphrodisiac before it kills you," she says. Victorian ladies often kept an angel’s trumpet flower on their card tables and added small amounts of its pollen to their tea to incite an LSD-like trip. "[Angel's trumpet] is an amazing way to die because it's quite pain-free," the duchess says. "A great killer is usually an incredible aphrodisiac."
Other familiar but potentially toxic plants include not only foxglove, but also belladonna, and poppies. Though castor oil comes from Ricinus communis, castor beans are the source of the deadly Ricin.
I am personally allergic to tomatoes and everything about lantana. Birds can eat the lantana berries. They are common and very pretty landscape plants; birds distribute the seeds, too.
Oleander is another beautiful but poisonous plant in all of its parts, flower, leaf and stem. In rhubarb the stem is edible but not the leaf.
Before planting anything, check with your county extension service or local nurseries or universities to find out the local toxic plant list.