Planting of new mint fields primarily occur in the spring or the fall. To begin a new field, the ground is disked, chiseled, and tilled smooth, thus providing a suitable planting area. Mint plants do not produce seeds; instead, rhizomes or stolons (rootstocks) are used to start new fields. Approximately 10,000 rootstocks are necessary to plant one acre. An acre of well-established mint will typically yield enough rootstock to plant between 10 - 15 acres.
The use of certified mint rootstock in establishing new fields reduces the chance of acquiring disease, weeds, or insects that may already be contained in contaminated planting material. Soil and rootstock from transported material can harbor pests and devastating diseases such as Verticillium wilt. These transported pests can reduce first year mint fields by 80%. Although planting certified mint rootstock is a large initial investment, it lowers pesticide input, increases mint yield and overall field health. The lush growth of mint and high humidity from irrigation provides suitable habitat for many natural enemies. Established mint fields receive minimal cultivation, largely because tillage practices tend to increase the spread of Verticillium wilt. A newly planted field will produce the first year, but at a lower yield than subsequent years. A healthy mint field will stay in production for about 3 to 4 years.
Typical crop rotation is about 10 years which includes 3 to 4 years of mint followed by 4 to 6 years of rotation among beans, corn, onions, sugar beets, grains, and other crops.
Spearmint harvest begins around July 1 when plants are in full bloom, and continues through mid-August. Peppermint harvest begins late July when plants are 10% in bloom, and continues through September. Delayed harvest past optimum maturity will cause a rapid deterioration of mint oil quality. About 10% of peppermint and most spearmint farmers harvest twice during the growing season.
To begin with, mint is swathed and dried in windrows to about 30% moisture content, picked up by choppers and blown into tubs, then hauled to the mint distillery. Because mint oil is insoluble in water, steam is used to extract the oils. A high-pressure boiler generates steam for the tub. Steam is injected through perforated pipes from the bottom of the tub and filtered upward. After distillation, the steam-vaporized mint oil is condensed. The mint oil, lighter than water and insoluble, floats to the surface of the receiving barrel and is collected in pure form. The oil is then drained off the top and placed in 55-gallon drums for storage or shipment to buyers.