Peppermint (Mentha piperita) is a perennial of the mint family, frequently found growing wild in moist situations throughout the eastern half of the United States. It is cultivated on a commercial scale, chiefly on the muck lands of southern Michigan and northern Indiana. The volatile oil forms the principal marketable product, but there is some demand in the crude-drug trade for the dried leaves and flowering tops.

Peppermint is propagated from "roots," or runners, which should be set in an almost continuous row in furrows about 3 feet apart and covered to a depth of about 3 inches. It can be grown on any land that will produce good crops of corn, but is most successful on the muck lands of reclaimed swamps. On uplands it soon exhausts the soil and will not do well for more than two or three seasons without the rotation of crops. On rich muck lands it will grow for a number of years, the soil being plowed after the crop is harvested and the runners turned in to form a new growth the succeeding year. It is essential that the ground be kept free from weeds, since their presence in the crop at harvest would seriously injure the quality of the oil.

When peppermint is grown on reclaimed swamps or muck lands fertilizers are rarely needed, but on uplands it is well to plow in 12 or more tons per acre of rotted stable manure before planting. Similar applications may be made between the rows in early spring and plowed in as the land shows signs of exhaustion. Commercial truck or potato fertilizers cultivated in between the rows at the rate of 600 pounds to the acre have proved useful in keeping up fertility, but manure is to be preferred, as it provides humus or vegetable matter as well as increases the fertility.

Harvesting is begun in July or August, when the plants are in full bloom. The herb is cut and cured like hay, and when fairly well dried is placed in large vats or stills having a capacity of from 1 to 3 tons of dry herb and distilled with steam to obtain the volatile oil. The yield of oil is exceedingly variable, but on lands well suited for the production of peppermint the average yield is not far from 30 pounds per acre. The annual production of peppermint oil in the United States is about 300,000 pounds. For many years before the war the price of the oil varied from year to year, but averaged about $2.50 a pound. There is some demand for the dried leaves and tops, for which 6 to 15 cents a pound was paid to collectors in June, 1920.

For further information on the growing of peppermint, see Farmers' Bulletin 694, entitled "The Cultivation of Peppermint and Spearmint."