Draft:Photoperiod Cannabis

Photoperiod cannabis (also known as short‑day or day‑length sensitive cannabis) refers to cannabis varieties whose transition from vegetative growth to flowering depends on receiving a critical amount of uninterrupted darkness each day, rather than flowering based on age.

Overview

Photoperiod cannabis plants require a reduction in daylight hours—typically to around 12 hours of light and 12 hours of darkness—to initiate flowering. Unlike day‑neutral (autoflowering) varieties, they will remain vegetative indefinitely if exposed to extended light periods. Most pure indica strains flower in approximately 6–9 weeks, while sativa strains may take 8–12 weeks to flower.

Recent research has shown that both photoperiod and light quality significantly influence not only flowering but also cannabinoid production. One study on the medical cannabis cultivar "Hanma 11" found that adjusting photoperiod and light spectra could optimize cannabidiol (CBD) yield and reduce energy consumption.

Origins

These photoperiod‑dependent cannabis varieties descend from wild *Cannabis sativa* and *Cannabis indica*, which evolved to flower in response to seasonal changes in daylight—typically late summer to early autumn. This trait allowed them to complete flowering before colder weather. In contrast, *Cannabis ruderalis* flowers based on age, regardless of day‑length.

Characteristics

Photoperiod cannabis is characterized by:

• **Light‑cycle dependent flowering** – Requires 10–12 h of continuous darkness daily to flower; exposure to light during the dark period can delay or prevent flowering.
• **Variable flowering time** – Indica‑predominant cultivars finish in ~6–9 weeks, sativa‑dominant ones in 8–12 weeks.
• **Potential for larger plants and yields** – Longer vegetative phases under extended light promote greater vegetative growth and yield compared to autoflowers.
• **Light spectrum and cannabinoid response** – As shown in one study, “varying photoperiods and light qualities” can significantly affect CBD yield in photoperiod cannabis; optimized light regimens improved metabolite production while reducing energy usage. :contentReference[oaicite:1]{index=1}

Cultivation

Indoor growers typically maintain an 18/6 light/dark cycle during vegetative growth, then switch to 12/12 to trigger flowering. Outdoor plants naturally flower as daylight decreases in autumn. Once initiated, flowering lasts 6–12 weeks depending on lineage.

Effects on cannabinoid yield

A recent study on "Hanma 11" showed that shifting photoperiod and light spectrum could enhance CBD yield and reduce energy consumption. The authors noted:

“The combined optimization of photoperiod and light quality resulted in a statistically significant increase in cannabidiol yield per unit of energy consumed.” :contentReference[oaicite:2]{index=2}

This demonstrates that light management in photoperiod cannabis goes beyond timing—it also affects the efficiency and potency of cannabinoid production.

Breeding

Crossing photoperiod strains enables selection for traits such as:

• **Faster flowering** – breeding hybrids to initiate and complete flowering more rapidly.
• **Balanced morphology** – combining compact indica traits with tall sativa characteristics.
• **Optimized cannabinoid profiles** – selecting alleles that respond well to specific light regimens, maximizing THC/CBD under controlled spectra and photoperiod.

Breeding typically involves crossing chosen parents, stabilizing through F₂/F₃ generations, and selecting for consistent flowering‑time alleles responsive to day‑length and light quality.

Advantages and disadvantages

Advantages

• Larger yields and plant size via extended vegetative growth.
• Full control of flowering timing through light-cycle manipulation.
• Potential to enhance cannabinoid yield per energy unit by optimizing light spectra and photoperiod.

Disadvantages

• Requires strict light/dark schedules—light leaks can cause stress, delay, or hermaphroditism.
• Outdoor cropping often limited to one harvest per season in most climates.
• Demands more time, space, and oversight than autoflowering varieties.

See also

• Cannabis cultivation
• Autoflowering cannabis
• Cannabis ruderalis
• Cannabis strain