Lavandula is a genus of aromatic evergreen shrubs in the mint family, Lamiaceae, with 47 accepted species. Also known by the name lavender, there are many widespread and well-known species and a huge range of cultivar have been developed. Species in this genus range in hardiness from H2, tender down to 5 degrees Celsius all the way to H5, hardy to -15 degrees Celsius. Some are well suited for hedging, such as L. angustifolia 'Hidcote'. Others have variegated or silver-coloured foliage or flower in different colours such as pink or white. They are native to the Old World with a wide distribution and have become naturalised in many countries. They have a variety of leaf forms from simple to pinnately-divided, all hairy, and whorls of usually violet tubular flowers. Some species, for example L. angustifolia or English lavender, have long been cultivated as garden herbs for their aroma and for essential oils. The optimal time to plant is between April and May as the soil is warming up. Lavandula plants are well suited to soil in poor to moderately fertile condition, it should be free-draining as they like to be on the dryer side. Copes well with chalky or alkaline soils, when grown in clay or clay loam, they tend to be short-lived and develop woody bases. The addition of organic matter and gravel to clay soil and using elevation by planting in mounds can help prolong the life of lavender plants in clay-heavy sites.