A groundbreaking study from the University of Wisconsin-Madison has shed new light on how temperature affects three crucial aspects of cannabis cultivation: flower weight, CBD content, and the production of purple pigments called anthocyanins. The research, published in the Journal of Cannabis Research, offers valuable insights for both indoor and outdoor growers seeking to optimize their harvests.

Key Findings

The study examined cannabis plants exposed to temperatures ranging from 0.5°C to 22°C during the flowering phase, revealing that different plant characteristics respond uniquely to temperature changes.

Flower weight and CBD production: Both inflorescence dry weight and CBD concentration increased consistently with rising temperatures. Plants grown at 22°C produced the highest yields (2.1g per plant) and CBD levels (5.2%), while those at 0.5°C yielded the lowest (1.0g per plant and 3.4% CBD respectively). Importantly, the researchers found these increases were primarily linked to plant maturity rather than temperature-induced stress responses.

Purple Pigmentation Tells a Different Story: The production of anthocyanins—the compounds responsible for purple coloration in cannabis—followed a completely different pattern. Maximum purple pigmentation occurred at moderate temperatures of 8°C and 15°C, with significantly reduced coloration at both extremely cold (0.5°C) and warm (22°C) temperatures.

Practical Implications for Growers

The research suggests that cannabis cultivators face a trade-off when growing purple varieties. While warmer temperatures (around 22°C) maximize yield and CBD production, cooler temperatures (8-15°C) are essential for developing the striking purple colors that command premium prices in many markets.

For indoor growers using controlled environments, the study indicates that a strategic approach could involve growing plants at optimal temperatures for development (22°C) and then applying a controlled cooling period (8-15°C) during late flowering to enhance purple pigmentation without significantly compromising yield.

The researchers also tested fluctuating temperature regimes, alternating between 4°C and 22°C to achieve the same average temperatures as constant conditions. Interestingly, these fluctuating conditions reduced anthocyanin production compared to constant moderate temperatures, suggesting that steady, moderately cool conditions are superior for purple development.

Visual Assessment Breakthrough

One particularly useful finding for commercial growers was the strong correlation (0.7-0.8) between visual purple coloration and actual anthocyanin content measured through laboratory analysis. This suggests that experienced cultivators can reliably assess anthocyanin levels through visual inspection, eliminating the need for expensive laboratory testing.

Scientific Significance

The study used a day-neutral cultivar (Early Harvest 118 S3) that was specifically bred for consistent purple expression, allowing researchers to isolate temperature effects from genetic variability. The plants were grown under controlled LED lighting for 30 days during the flowering phase, ensuring that temperature was the primary variable affecting the measured outcomes.

Looking Forward

This research provides cannabis cultivators with evidence-based guidance for optimizing their growing environments. Whether prioritizing yield, CBD content, or aesthetic appeal through purple pigmentation, growers now have scientific data to inform their temperature management strategies.

The findings are particularly relevant as the legal cannabis industry continues expanding, with consumers increasingly seeking products that combine high potency with visual appeal. Understanding how environmental factors influence these characteristics gives growers powerful tools for meeting diverse market demands while maximizing the value of their crops.

study link - https://jcannabisresearch.biomedcentral.com/articles/10.1186/s42238-025-00311-w