Pennyroyal (Hedeoma pulegioides) is an annual plant, flowering from June to October, and is found in dry soils from Nova Scotia and Quebec to Dakota and southward. Both the dry herb and the oil obtained therefrom by steam distillation form marketable products.

Pennyroyal grows well on average upland soils and is frequently abundant on sandy or gravelly slopes. In field planting the seeds should be sown in rows in the fall and covered not to exceed one-quarter of an inch, since they rarely germinate if planted at a greater depth. The plants come up early in the spring, and to secure the best results clean cultivation and freedom from weeds are essential, as with all cultivated crops.

Early in the summer, when the plants are in full flower, they may be mowed. To prepare the herb for market the plants are dried, preferably in the shade, and carefully packed immediately after drying. All the large stems should be removed in order to improve the quality of the product. The herb should be marketed promptly, since it deteriorates with age. For the production of the volatile oil, the plants should be harvested when in full flower and distilled without drying.

Returns from experimental areas indicate that a yield of about 1,200 pounds of dry herb per acre may be expected. The yield of oil varies from 15 to 30 pounds per acre. The price paid for the dry herb usually ranges from 1 to 2 cents a pound. The wholesale price of the oil ranges from about $1 to $2 a pound.