Cannabis Flower Room

Cannabis plants nearing harvest in a greenhouse

What is a Flower Room?

A flower room is a dedicated space where cannabis plants enter their final growth stage after the vegetative phase. Here, light cycles are adjusted to 12 hours on, 12 hours off, triggering flowering. Careful control of temperature and humidity ensures healthy bud development, preparing the plants for harvest.

At a certain point, dependant on the grower’s style, the light schedule will be changed to twelve hours on, twelve hours off, to mimic the shortening of days in late summer and fall. This triggers flowering and a final “stretch” growth phase in early flower, before the plant attempts to reproduce by making flowers. Dried cannabis flower as an end-use product is the collection of calyxes (unpollinated seed sacs) of female plants; thus, growers do not want male plants anywhere in the facility. Pollination produces seeds; while this is desirable for breeding, it is not desirable in dried cannabis flower. On these calyxes and sugar leaves, the trichomes develop; this is where cannabinoids such as tetrahydrocannabinol (THC), cannabidiol (CBD) and many more are concentrated.

The flower stage is the most dynamic of all stages, with the most changes from day to night, day to day and week to week. Lighting in the flower stage is the most intense of all. In the early stages of flower, the room is sparsely populated with the canopy becoming denser over the weeks as the stage progresses. When the flower stage is complete, the plants are harvested, the room is cleaned and sanitized and eventually repopulated with a new batch of young plants that have completed the vegetative stage.

The plants begin the flower phase as a mature vegetative plant and conclude at their largest size. Not surprisingly, roughly 75% of the physical space in the facility is devoted to plants in the flower stage. The climate equipment for this stage needs to be very responsive to deal with the variation in heat and humidity loads, handle the most dynamic range of setpoints, and provide the most airflow to pick up humidity in the densely packed canopy.

For more details on optimizing grow spaces, visit our page on efficient cannabis facilities.

Mother room for cannabis cultivation in greenhouse facility

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Engineering the optimal flower room

Room Function

Cannabis plants that have reached their desired size, are either brought to a flower room or the conditions of the area are geared towards that of a dedicated flower room. Here, the plants enter a generative phase by adapting light cycles. To avoid undesirable fungi, sickness or pests and to prepare for a flower that can properly be dried and cured, control over humidity is key.

Light Schedule & Intensity

The photo period is twelve hours light on, twelve off. As the flower stage progresses, the room is gradually made cooler and drier, simulating the progression of the fall season. The change in setpoints from week to week will depend on what the grower wants based on their style or “recipe” for the strain.

Temperature & Humidity

A grower will want a moderate amount of warmth in the room (75°F–82°F/23°C–28°C) and very high humidity locally, at the plant. In fact, for the first week the clones may be covered with a dome to achieve almost 100% RH at the leaf surface.

Vapor Pressure Deficit

The flower room has the broadest ranges of temperature (70°F–82°F/21°C–28°C) and humidity (40% to 60% RH). Flower rooms by their very nature are the most complicated rooms to maintain conditions in and truly expose the flexibility and quality, controlling by VPD can allow consistency accros the different varieties.

Flowering room for cannabis cultivation in greenhouse facility

Cannabis plants thriving in a Dutchgreenhouse