Photoperiod manipulation is the practice of managing a plant’s exposure to light and dark cycles. Most often, this is achieved indoors or in isolated growing rooms with lights on timers, or else lights are adjusted manually. Outdoors, this is usually achieved with structures around the plant that support shades or coverings to block sunlight. In greenhouses, shades are often rigged to be pulled over whole sections of the structure.
The goal is usually to prompt the plant into flowering early, and in doing so, fit more life cycles into a single growing season.