Why Is Some Marijuana Purple?

By Dr. Daniela Vergara

Not much research has been done on why Cannabis sativa turns purple, but there have been studies on other plants. That helps us understand what might be going on in C. sativa too.

What Makes Marijuana Purple?

Purple flowers in marijuana are usually caused by pigments called anthocyanins. These are the same pigments that give blueberries, grapes, and other fruits their red, purple, or blue color [1].

Every plant’s appearance (called a phenotype) is shaped by both genetics and environment. For some cannabis varieties, growing conditions may have a bigger effect on color. For others, the color is mostly due to genetics.

What Produces Purple in Plants?

The purple color in plants comes from a group of water-soluble pigments called anthocyanins. They’re found in many plants, including trees like pines and flowering plants.

Anthocyanins are part of a bigger group of compounds called flavonoids. Their main job is to give purple, blue, or red colors to flowers, fruits, and leaves [1].

Types of Anthocyanins

The most common anthocyanins in plants are:

• Cyanidin (most common)
• Delphinidin
• Pelargonidin
• Peonidin
• Malvidin
• Petunidin

Cyanidin and delphinidin make red and purple colors. Pelargonidin makes red and orange. Yellow and orange colors can also come from other compounds called carotenoids [2, 3].

Why Do Plant Colors Change?

Green color in plants comes from chlorophyll, which is found in chloroplasts—the parts of the cell where photosynthesis happens.

When a plant gets older (a process called senescence), its chlorophyll starts to break down, especially during the fall. When this happens, other pigments become more visible:

• Carotenoids (yellow/orange) are always in the plant but hidden by chlorophyll.
• Anthocyanins (purple/red) are often made right before the leaves fall.

This is why we see red, purple, yellow, and orange colors in trees during autumn [3].

What About Purple Marijuana?

Some cannabis strains such as Purple Urkle, Purple Kush, and hemp varieties like Red Petiole [4], are purple. Their color isn’t always caused by aging.

So why are some cannabis plants, like the ones mentioned above,  naturally purple all the time? We don’t fully know. Some other plants, like mango trees, zebrina, or begonias, are also purple or red year-round. But the exact reason for these colors, outside of aging, is still unclear [3].

What Makes Marijuana Change Color?

The amount and color of these pigments can change depending on the plant’s genes, the temperature, and the soil pH [2]:

• In acidic soil, anthocyanins look red
• In neutral soil, they look purple
• In basic soil, they look blue 

Cooler temperatures may also boost anthocyanin production. One idea is that the red pigments help protect the plant from cold-related light damage. Some C. sativa plants turn purple or red over time, possibly due to aging (senescence), temperature drops, or both [2, 3].

Why Does Marijuana Turn Purple?

Purple marijuana comes from genes that turn on anthocyanin production. These changes can also be triggered by the environment, which affects how genes are expressed, or by epigenetics which are changes in gene activity that occur without altering the DNA sequence [5].

Some varieties are always purple because of their genetics, while others only change color under the right environmental conditions, especially cooler temperatures.

This raises more questions:
Do always-purple plants have different genes, or do they just use the same genes differently depending on the environment? This raises more questions on how much of cannabis color is due to genetics (nature) and how much is due to environment (nurture) or probably a mix of both as with most phenotypic traits.

Can Indoor Light Cause Purple Color?

It’s possible. Light conditions in indoor grows might trigger anthocyanin production [6]. Studies have shown that light changes can affect plant color in other crops like strawberries.

Medical Uses of Anthocyanins

Anthocyanins are popular in medicine and wellness because they are safe and may offer health benefits. They may help with [7, 8]:

• Cancer
• Heart disease
• Diabetes
• Brain health
• Weight control 

Some studies suggest anthocyanins in red wine may help prevent heart disease. So maybe smoking purple weed brings some peace of mind, even if it’s not a proven health cure.

Purple Flowers Aren’t Just on Female Plants

Here’s something surprising: male cannabis plants can also grow purple flowers! This was new to me too, since I mostly work with females. And just like females, the color in males can vary a lot.

Marijuana Plants with Purple Stems

I’ve also seen cannabis plants with purple stems! As I mentioned earlier, C. sativa shows a lot of variation, not just in its DNA (genome) but also in its physical traits (phenotype).

References

1. Seitz, H. and W. Hinderer, Anthocyanins. Phytochemicals in Plant Cell Cultures, 1988: p. 49-76.

2. Khoo, H.E., et al., Anthocyanidins and anthocyanins: Colored pigments as food, pharmaceutical ingredients, and the potential health benefits. Food & nutrition research, 2017. 61(1): p. 1361779.

3. Archetti, M., et al., Unravelling the evolution of autumn colours: an interdisciplinary approach. Trends in ecology & evolution, 2009. 24(3): p. 166-173.

4. Di Candilo, M., et al., Two new fibre hemp genotypes. Morphology and yield traits [Cannabis sativa L.]. Sementi Elette (Italy), 2000.

5. Enaru, B., et al., Anthocyanins: Factors affecting their stability and degradation. Antioxidants, 2021. 10(12): p. 1967.

6. Magagnini, G., G. Grassi, and S. Kotiranta, The effect of light spectrum on the morphology and cannabinoid content of Cannabis sativa L. Medical Cannabis and Cannabinoids, 2018. 1(1): p. 19-27.

7. Mukherjee, P.K., Quality control and evaluation of herbal drugs: Evaluating natural products and traditional medicine. 2019: Elsevier.

8. Pietta, P., M. Minoggio, and L. Bramati, Plant polyphenols: Structure, occurrence and bioactivity. Studies in natural products chemistry, 2003. 28: p. 257-312.