With their tall spires of flowers these are a popular garden perennial. Although most cultivated hybrids bloom in early summer, mainly in shades of blue, there are many species that flower in spring or late summer and have flowers in almost every possible colour. All parts are poisonous.
There are more than 350 different species, which are almost entirely native to the northern hemisphere, with the exception of a few species that grow in the mountainous regions of East Africa. Most are found in California and western China.
These grow best in a sunny position, with fertile, but well-drained soil.