Article Highlight | 25-Jul-2025

How light and hormones shape cannabis flowers

Nanjing Agricultural University The Academy of Science

Flower development in cannabis is key to its therapeutic and industrial potential, but how this complex process is regulated has remained unclear. In a new breakthrough, researchers discovered that while young cannabis plants initiate solitary flowers regardless of light conditions, mature plants require sustained short-day (SD) exposure to form tightly clustered inflorescences. This floral transformation hinges on reduced levels of gibberellin, a plant hormone known for promoting stem growth. When gibberellin levels rise—either through long-day (LD) light exposure or artificial application—inflorescence structure breaks down, flowers become dispersed, and cannabinoid production declines. The findings shed new light on how environment and hormones jointly orchestrate cannabis reproduction.

Cannabis sativa L. serves diverse purposes—from fiber and seed oil production to medical and recreational use—each of which depends heavily on the timing and density of its female flowers. The shape and compactness of inflorescences directly affect yield and the concentration of bioactive compounds like THC and CBD. While early flowering is known to proceed independently of photoperiod, the factors that drive full floral maturation have remained obscure. Gibberellins have long been implicated in flowering control across plant species, but their precise role in cannabis has been murky. Due to these complexities, further in-depth research is needed to unravel the interplay between photoperiod and hormones in cannabis flower development.

A research team from the Volcani Institute in Israel has uncovered critical mechanisms behind cannabis flowering, as reported (DOI: 10.1093/hr/uhae245) in Horticulture Research on September 3, 2024. By combining light cycle experiments with hormone treatments and detailed physiological analyses, the team showed that short-day (SD) photoperiods initiate and sustain inflorescence development by keeping gibberellin levels low. Reversing light conditions or applying gibberellin externally disrupts this balance, leading to elongated stems and scattered flowers. These findings redefine how we understand cannabis reproductive biology and open new pathways for agricultural optimization.

The study revealed a two-phase response to SD lighting in mature cannabis plants. Initially, plants undergo a growth spurt with rapid stem elongation, but by day 10, internode elongation halts and compact flower clusters begin to form. This transition correlates with declining levels of GA4 and auxin in the shoot apex. Researchers found that just three days of SD exposure were sufficient to trigger inflorescence initiation, but continuous SD was essential to maintain it. Reverting to long-day (LD) conditions restored hormone levels, reversed floral clustering, and prompted a return to vegetative growth.

Further experiments confirmed the hormonal link: exogenous gibberellin application under SD conditions mimicked the effects of LD exposure—disrupting compact flower development and significantly lowering key cannabinoids like THC and CBD. Meanwhile, auxin treatments had minimal impact, underscoring gibberellin's dominant role. The study also highlights that gibberellin may directly inhibit cannabinoid biosynthesis or alter trichome development, both of which affect cannabis potency. Altogether, the findings illustrate a finely tuned hormonal system governed by light cycles, where gibberellin acts as a master switch for floral architecture and chemical output.

“Cannabis inflorescence development is a reversible, hormone-dependent process that requires a precise photoperiod,” said Dr. Ben Spitzer-Rimon, lead author of the study. “Our results show that even after flowers begin to form, returning to long days or increasing gibberellin levels can dismantle the process. This insight could transform how we manage flowering stages in cultivation—making cannabis production more predictable, controlled, and efficient.”

These findings have direct applications for commercial cannabis cultivation. Understanding that continuous SD lighting is required to maintain flower clusters gives growers a powerful tool to time flowering precisely and avoid disruptions that can lower quality. Additionally, manipulating gibberellin levels offers a new way to control plant architecture and potentially boost cannabinoid yields. For the pharmaceutical industry, where flower density and chemical consistency are critical, this study offers a hormonal roadmap for optimizing production. As the cannabis sector continues to expand globally, insights like these will be pivotal in refining growth protocols and breeding strategies.

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References

DOI

10.1093/hr/uhae245

Original Source URL

https://doi.org/10.1093/hr/uhae245

Funding information

The plant material (rooted cuttings) was supplied by Canndoc Ltd, a certified commercial cultivation producer in Israel. We are grateful for the cooperation and advice of Neri Barak, the founder and president of Canndoc Ltd. This work was supported by the Chief Scientist of the Israeli Ministry of Agriculture and Rural Development grant 20-01-0177.

About Horticulture Research 

Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.

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