Date of Award:

5-2026

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Plants, Soils, and Climate

Committee Chair(s)

Bruce Bugbee

Committee

Bruce Bugbee

Committee

Royal Heins

Committee

Jim Faust

Committee

Matt Yost

Committee

Erik Runkle

Abstract

Cannabis (Cannabis sativa) is a plant of increasing importance for research, medical, recreational, industrial, and agricultural purposes, but a strict legal landscape means that it was chronically understudied. Now that research institutions can utilize this plant for study, we require updated terminology to describe various cannabis flowering types that occur under ideal and non-ideal growing conditions. We introduce new flowering terminology and describe them in text and with photographs.

Plants use light as a resource to power photosynthesis, and a greater total sum of photons generally increases yield. In controlled environment agriculture where growers utilize light fixtures instead of the sun, the total photon sum can be increased by increasing the light intensity or increasing the amount of time the lights are on during a 24-hour period. But, cannabis requires an uninterrupted dark period of sufficient duration in order to flower, which means that the light period cannot be increased past a certain number of hours. Our studies looked at the impact of variable photoperiod length on flowering, early reproductive development, and yield across diverse cannabinoid cannabis cultivars, and found that longer photoperiods favored vegetative growth over reproductive yield. Yield did not increase even when the total photon sum was increased under longer photoperiods due to the decreased flowering stimulus.

Plants also use light as a source of information, especially the duration of the light and dark periods, which allows plants like cannabis to flower at the same time. When light from a human-caused source is present during the dark period, the signal disrupts plant timekeeping and decreases the strength of flowering, which can sometimes be prevented entirely. The intensity, color, timing, and total photon sum of light during the dark period all impact flowering response. From our studies, we developed a model that allows users to predict flowering response in cannabis based on information about the light provided to plants during the otherwise dark period.

In this dissertation, we introduce new flowering terminology and showcase the value of cannabis as a model to investigate the effects of light as a resource and a source of information in flowering plants.

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

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