3. Foxglove (Digitalis purpurea)
Featuring tall spikes with a multitude of bell-shaped purple-pink flowers, each bloom of the foxglove plant has an intriguing smattering of black and white spots on its interior cup. While it certainly is a fascinating visual piece for the garden, all parts of this plant contain cardiac glycoside, a digitoxin that affects the heart. If eaten, it causes low pulse rate, nausea, vomiting, and heart contractions that will eventually lead to cardiac arrest.
4. Lily of the Valley (Convallaria majalis)
Sweetly scented, lily of the valley has leafy shoots with a delicate cluster of downward-facing white flowers. This dainty little number is not only extremely toxic, but could easily be classed as an aggressive grower too. To date, 38 different cardiac glycosides have been identified in lily of the valley and consuming even small amounts can cause abdominal pain, reduced heart rate, skin rashes, and blurred vision. Lily of the valley also produces small red berries, which are poisonous too, and could be especially tempting to children.
These plants are the veritable bullies of the garden, quickly subduing and crowding out your more bashful botanicals. If you decide to plant these types of blooms regardless of their aggressive nature, be prepared to snip and pull quite often to keep them under control.