This section is from the book "Commercial Gardening Vol4", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
"Sweet" Lavender is an important crop commercially in the neighbourhood of Mitcham, Surrey, and in parts of Hertfordshire around Hitchin and Elsenham. Small plants are largely grown for sale by many nurserymen.
The Lavender is a shrubby South European plant about 3 ft. high, with grey or hoary leaves, and long erect spikes of bluish-purple flowers in July and August. The plants flourish in any ordinary garden soil, but prefer a rather heavy loam on a chalky subsoil, and sunny situations sloping to the south. They are increased by slips or cuttings taken in August or September, and inserted in sandy soil under lights if possible. They root well by the following March, April, or May, and are then or the following autumn planted out about 1 ft. or 18 in. apart, and are often intercropped with Lettuces, Parsley, or other crops. The following year the plants in alternate rows are lifted to make a new plantation, thus leaving the others in rows about 3 ft. apart, or about 4840 to the acre. The ground is well dug, and hoed occasionally every year, and when the plants are about seven years old they are dug up, and new plantations are made.
In July in early seasons, but usually in August, the flower spikes are cut with sickles. The flowers are distilled to extract the pale-brown-coloured oil, which is worth about £8 per 4 1/2-lb. bottle. The average yield per acre is about 25 lb. of oil, but in good seasons this is surpassed. About 600 cwt. of flowers are required to produce this quantity.