Newry's Blue was bred around 1900 in Ireland, and it's a favorite among gardeners to this day for its remarkably deep blue flowers and dense spires. At 4 to 5 feet tall, it's a regal presence at the back or the border, so if you've had difficulty growing delphiniums, this perennial is a great alternative. Unlike delphiniums, it usually doesn't need staking. But do handle with care. The roots are poisonous and the leaves can cause skin irritation.

Aconitums are commonly known as monkshood, because the upper sepal of each flower forms a protective hood like the ones worn by medieval monks. Another common name, wolfbane, refers to the poison made from this plant's roots, which was used to tip hunting arrows. On a more positive note, Aconitums attract a variety of butterflies and moths, and are the primary food source for Old World bumblebees.