The plants are cut late in the summer when in full flower, the leaves and tops being separated from the stems and dried without exposure to the sun, as the trade desires a bright-green color. For the volatile oil the plants are allowed to lie in the field after cutting until they have lost a considerable portion of their moisture. They are then brought to the still and the oil removed by the usual method of steam distillation.
A yield of about 2,000 pounds of dry leaves and flowering tops per acre may be obtained under good conditions. The yield of oil varies, but about 20 pounds per acre is a fair average. In the United States the center of production of oil of tansy is Michigan, where about 2,500 pounds are distilled annually. The price of the oil in June, 1920, was about $8 a pound. The price of the leaves and tops usually ranges from 3 to 5 cents a pound.
[THYME.]
Thyme (Thymus vulgaris) is a shrublike perennial plant of the mint family, native to southwestern Europe. It is a common garden plant, which lives for many years under good culture. The herb, often used for seasoning and flavoring, yields the oil of thyme, which has well-recognized medicinal properties.
Thyme grows well from seed, which may be sown early in the spring in drills 3 feet apart, or the plants may be started in a greenhouse or in seed beds outside and later set at intervals of about 18 inches in rows 2 to 3 feet apart. Thyme may also be propagated, like geraniums, from cuttings rooted in sand under glass. The plants grow well in mellow upland soil of good quality, and should be well cultivated and kept free from weeds throughout the growing season.
For preparing the dry herb only the flowering tops are used, and these are cut when the plant is in full bloom and carefully dried in the shade in order to preserve the natural color. The volatile oil is obtained from the entire herb, which is preferably cut when in full flower and subjected to steam distillation without previous drying.
Returns from experimental areas have shown great variations in the yield, which has averaged about a ton of green herb per acre. Normally the yield from a planting increases for several years, as the plants become better established, and yields at the rate of about a ton of dry herb per acre have been reported. The wholesale price in June, 1920, for the dry herb ranged from 11 to 15 cents a pound; for the imported oil, from $1.85 to $2.25 a pound, according to quality.