This section is from the book "Commercial Gardening Vol2", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
This is the best known of many species. It is a trailing hairy perennial about 4 in. high, with linear leaves and deep-blue flowers. The variety "Heavenly Blue" is much deeper in colour. Other kinds are: canescens, 9 in., yellow; Gas-toni, 1 ft., sky blue with a white eye; grami-nifolium, 1 ft., with long grass-like leaves and blue flowers; petroeum (now known as Moltkia), 9 in., pinkish purple to violet blue; purpureo-coeruleum, 1 ft., deep purple; and rosmarini-folium, 9 in., a small bushy plant with Rosemary-like leaves and bright-blue flowers. These plants are excellent for the rock garden, and grow in ordinary good soil. They are increased from seeds, cuttings in cold frames, and by division of the roots.