This section is from the book "The Gardener V1", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
Several species of this fine genus are admirable subjects for ornamental borders of hardy flowers. They are profuse-blooming, showy plants, which should be in every good selection of herbaceous plants. Any good garden-soil suits them well. They are easily increased by division, and also by cuttings - the latter in autumn, the former at any time after growth is fairly matured, which is after flowering ceases.
A very distinct and handsome species. It forms compact tufts about 9 or 12 inches high. The flowers are produced in whorled spikes, are bright blue, in form Pentstemon-like, opening in July. It likes a warm, sunny situation, and is rather impatient of continuous wet at the roots. Native of Siberia.
A more erect-growing kind than the last, and freer flowering, but the flowers are smaller, though in the mass not less showy. They open in July, and last till September.