Purple Haze & Chilly Days

MCR Labs
3 min readAug 19, 2020

How Anthocyanins play a role in the coloration of cannabis plants.

By Michael Esposito — August 19, 2020

Many cannabis users fondly remember the point at which they upgraded from mids and KB to their first heady strain. No longer would they be resigned to coughing through the greenish-brown, sometimes barnyard scented, schwag weed they got from their friend’s older brother.

With the increased availability of craft cannabis, they are now able to enjoy flower with unique strain names, visible trichome heads, and depending on the variety, rich pink and purple hues. What is it about these particular buds that allow them to present such beautiful colors? The answer to this is the production of a specific family of compounds called anthocyanins.

What are Anthocyanins?

Anthocyanins are found in a huge variety of plants, ranging from the purple blades of grass poking through the cracks in the parking lot in late fall to the stinky blinky skunk skunk lovingly produced by cultivators across the world.

There are many different types of anthocyanins, and they have been detected in most tissues of all types of plants, from food crops to ornamental flowers. The expression and types of anthocyanins present in plant tissues are determined by a number of factors, including the genetic makeup of a plant, environmental conditions like temperature and light, as well as factors of soil chemistry like pH and nutrient availability. In fact, anthocyanin presentation is so tightly linked to soil pH that its presentation is often used as a natural pH meter, allowing a gardener to perform a basic analysis of their soil based solely on how it makes their flowers look. A pink hydrangea for instance, indicates a soil with a more alkaline pH. That same hydrangea in soil made more acidic will completely change its hue from pink to a delightful blue.

When summer shifts to fall, the production of anthocyanins tends to occur as a stress-response to lower temperatures. While leaves on the trees lose their chlorophyll and take on brilliant reds and oranges, commonly found weeds growing in sidewalks and yards begin to take on a purplish-maroon hue in response to the overnight chill. While the mechanisms behind anthocyanin production and increased cold-tolerance aren’t fully understood, the correlation is extremely apparent with lower temperatures causing an increase in production and higher temperatures suppressing the appearance of purple and red pigments in plants.

How can growers use Anthocyanins to achieve certain colors?

While not every strain of cannabis will have the anthocyanin production potential of a tenderly grown Peyote Purple phenotype, a curious grower can tweak their growing conditions in a number of ways to bring out the full colorational potential of their plants, including:

  • Dropping temperatures in late flower to mimic the chill of fall
  • Increasing the intensity of light to generate purple pigments as a stress response
  • Supplying or withholding certain nutrients
  • Experimenting with different pH conditions

These are all excellent ways to experiment with coloration in your grow. While you may have to sacrifice cannabinoid, terpene, and structural potentials of your flowers in order to bring out the darkest and most unique hues, being able to showcase a nug that looks so purple it’s almost black is something that the inquisitive cultivator should definitely attempt at least once in their lifetime.

Originally published at https://mcrlabs.com on August 19, 2020.

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MCR Labs

MCR Labs is an independent cannabis testing & research laboratory located in Framingham, Massachusetts devoted to cannabis safety and education.