Does Purple Mean More Potent? What the Research Shows

Watch the episode · 3:33

Your plant is turning purple. Is it stronger, is it stressed, or is it just cold? Online, purple gets blamed and praised for everything: extra potency, a hungry plant, a cold snap. So we went to the lab studies, and one found a purple cannabis leaf holding more than five times the pigment in blackcurrants.

The purple pigment ▶ 0:25

The purple is a pigment called anthocyanin, the same family that colours blueberries and red cabbage. It is made in the outer layer of the leaf and stored in tiny water-filled sacs inside the cells, where it works like a sunscreen. Most of the time green chlorophyll hides it. When the plant makes extra pigment, or the green fades late in flower, the purple shows through.

In an Italian study, a purple leaf held about 400 times more of this pigment than a green leaf on the same plant.

Source · Bassolino et al., Antioxidants (2023)

It's in the genes ▶ 1:00

So what flips the switch? First, and most important: genetics. In a Canadian study, four cannabis varieties grew side by side, under the same lights, in the same warm room. One stayed completely green, right down to its leaf stalks; the other three turned red and purple. The difference was in their genes. A chain of enzymes builds the pigment step by step, and the more active those genes were, the more purple the leaves.

Source · Gagalova et al., Plant Direct (2024)

It is why famous purple strains such as Granddaddy Purple turn purple so reliably: the colour was bred into them. And it is why purple stems on a healthy, fast-growing plant are usually nothing to worry about. Some genetics just colour their stems and leaf stalks from early on.

The cold-night trick ▶ 1:45

Genetics decides whether a plant can turn purple; temperature decides how much. In a 2025 trial, a hemp line bred to turn purple spent the end of flowering at different temperatures, from near freezing up to 22 °C. Purple peaked at 8 and 15 °C. At 22 °C there was less, and near freezing, almost none. So there is a sweet spot: cool, not frozen.

But does purple mean stronger? The cool plants were far more purple, but they had less CBD: 3.4% against 5.2% in the warm ones.

The researchers traced that to slower growth in the cold, not to the colour: plants given the same total warmth ended up with the same CBD. Purple changed the colour, not the strength.

Source · Kim et al., J. Cannabis Res. (2025)

When purple is a warning ▶ 2:31

But sometimes purple is a warning sign. Plants also make this pigment when they run short of phosphorus. So if purple arrives early, with slow growth and dull, sickly leaves, it may not be the genes talking. Check your feeding.

Source · Zhang et al., Front. Plant Sci. (2026)

The verdict ▶ 2:44

Purple buds late in flower? Genes, plus cool nights. Purple stems on a healthy plant? Usually just its genes. Purple with slow growth and sickly leaves? Check the feeding. And don't freeze plants for colour: near zero, the purple almost vanished.

Purple is a natural pigment. Genes decide whether a plant can make it, cool nights (not frost) deepen the colour, and purple doesn't mean more potent.