Flowering hemp
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Flowering Hemp: Insights from Recent Research
Cannabinoid Development in Flowering Hemp
The development of cannabinoids in hemp flowers is a critical aspect of hemp cultivation. A field study examining various hemp varieties found that total THC, CBD, and CBG levels significantly increased as the flowers matured, peaking around 6 to 7 weeks post-anthesis before declining as the plants senesced. Notably, day-length-sensitive varieties maintained THC levels above the 0.3% threshold from 4 weeks post-anthesis until the end of the growing season, whereas day-length-neutral varieties only exceeded this threshold during the peak weeks . This dynamic change in cannabinoid levels underscores the importance of monitoring flowering stages for optimal cannabinoid yield.
Photoperiodic Flowering Response
Photoperiod plays a crucial role in the flowering response of hemp cultivars. Research on 15 essential oil and 12 fiber/grain hemp cultivars revealed that flowering was delayed by longer photoperiods. Essential oil cultivars, for instance, experienced a delay of 1 to 2 days when the photoperiod exceeded 13 hours and up to 8 days when it exceeded 14 hours. Fiber/grain cultivars showed a similar delay pattern, albeit to a lesser extent . This sensitivity to photoperiod highlights the need for selecting cultivars adapted to local light conditions to optimize flowering and yield.
Flowering Control Mechanisms
The control of flowering in hemp is influenced by photoperiodic sensitivity and genetic factors. Hemp varieties grown in low latitudes with shorter day lengths tend to flower early, which can affect yield and quality. The activation or deactivation of genes in response to light duration, perceived by photoreceptive pigments, plays a significant role in this process. Additionally, the sexual dimorphism in hemp, determined by the XY chromosomal mechanism, is influenced by endogenous plant growth regulators that fluctuate with environmental variables . Understanding these mechanisms is essential for breeding and crop management.
Impact of Sowing Time on Flowering and Yield
Sowing time significantly affects flowering phenology and yield in hemp. Studies on monoecious hemp cultivars showed that earlier sowing dates resulted in higher stem and seed yields. For instance, mid-April sowing produced yields of approximately 12.5 t/ha for stems and 1.9 t/ha for seeds. The duration from sowing to flowering was a critical factor, with early sowing leading to better yields . This finding emphasizes the importance of selecting appropriate sowing times to maximize both stem and seed production.
Bee Diversity and Hemp Flowering
Hemp flowers, despite being wind-pollinated, attract a diverse range of bees due to their pollen-rich nature. A study conducted in northern Colorado identified 23 different genera of bees visiting hemp flowers, with the European honeybee (Apis mellifera) being the most dominant. This period of hemp flowering coincides with a dearth of other pollinator-friendly crops, making hemp a valuable pollen source for bees . This ecological interaction suggests that hemp cultivation can support pollinator populations, which is beneficial for broader agricultural ecosystems.
Inducing Male Flowers on Female Plants
To produce all-female hemp crops, which are preferred for higher CBD and THC yields, growers can induce male flowers on female plants using silver thiosulfate (STS) sprays. Research demonstrated that a 3 mm STS foliar spray was highly effective in converting female flowers to male flowers, facilitating the production of genetically female pollen . This technique is valuable for producing feminized seeds, ensuring uniform and high-yielding hemp crops.
Conclusion
The flowering behavior of hemp is influenced by a complex interplay of genetic, environmental, and management factors. Understanding these dynamics is crucial for optimizing cannabinoid production, improving yield, and supporting ecological interactions. Continued research and breeding efforts are essential to develop hemp cultivars that are well-adapted to various growing conditions and meet the demands of diverse applications.
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