Poisonous plant and classic Witch garden flowers. All of these plant while lovely are indeed toxic. For more information read my book "Garden Witches Herbal". There you will find a chapter devoted to Gothic Witch Garden Plants. -Ellen Dugan
Water Hemlock Most violent toxic plant in North America. Grows in meadows and along stream banks, it is the plant's roots that contain deadly sap that when touched or eaten, causes grand maul siezures and death.
Monkshood: Aconitum nagarum, dark purple form. I can't pin down a variety or a source for seeds, sadly. You will have to do a bit of sleuthing if you want one. Excellent for a poison garden; not so good if you have kids around.
Poisonous Plants: Hellebore species and hybrids: Helleborus viridis (top left); Helleborus foetidus (top right) with cross-section; flowers of various specimens of Helleborus × hybridus, including doubles.