29 CFR 780.106: Employment in “primary” agriculture is farming regardless of why or where work is performed.

When an employee is engaged in direct farming operations included in the primary definition of “agriculture,” the purpose of the employer in performing the operations is immaterial. For example, where an employer owns a factory and a farm and operates the farm only for experimental purposes in connection with the factory, those employees who devote all their time during a particular workweek to the direct farming operations, such as the growing and harvesting of agricultural commodities, are considered as employed in agriculture. It is also immaterial whether the agricultural or horticultural commodities are grown in enclosed houses, as in greenhouses or mushroom cellars, or in an open field. Similarly, the mere fact that production takes place in a city or on industrial premises, such as in hatcheries, rather than in the country or on premises possessing the normal characteristics of a farm makes no difference (see Jordan v. Stark Brothers Nurseries, 45 F. Supp. 769; Miller Hatcheries v. Boyer, 131 F. 2d 283; Damutz v. Pinchbeck, 158 F. 2d 882).