What makes cannabis purple
Red and purple colours in plants come largely from anthocyanins, as a 2024 study in Plant Direct puts it. These water-soluble pigments also colour berries, currants and grapes, according to a 2017 review in Food & Nutrition Research.
In cannabis, a 2023 study by Italian researchers at CREA and the University of Bologna identified cyanidin-3-rutinoside, also called keracyanin, as the main pigment in purple leaves, stems and flowers, the first time it had been reported in the plant (Bassolino et al., Antioxidants). The 2024 Plant Direct team compared 4 differently coloured cannabis varieties and found a set of pigment genes, including CHS, F3H, DFR and ANS, that tracked most closely with how much anthocyanin the leaves held. Its authors note that the genetics of cannabis pigmentation had not been well characterized before.
Genetics come first
Whether a plant colours up depends first on its genes. In the Italian study, cannabis lines grown at the same site differed widely in when colour appeared, which tissues coloured and the shade itself. Accession V18 kept red leaf stalks all season, while S1750 showed patchy colour during flowering and then turned purple from stem to flower between mid-September and the end of October.
That is why purple is tied to particular strains. Leafly says Granddaddy Purple, popularized in 2003 by Ken Estes, blooms in shades of deep purple, though its parentage is disputed. Leafly's Blueberry page notes that growers admire that strain for its colourful hues; see our Blueberry strain guide for more.
What cool temperatures do
Cool weather can deepen the colour in plants that carry the genes. In a 2025 University of Wisconsin-Madison study in the Journal of Cannabis Research, researchers grew an inbred cannabis line with uniform purple pigmentation at temperatures from 0.5 °C to 22 °C. Pigment peaked at constant temperatures of 8 °C and 15 °C and dropped at both 0.5 °C and 22 °C.
The authors note that across many plant species, temperatures below about 20 °C tend to promote anthocyanins and warmer ones suppress them, though the details vary by species. So colder is not simply better: near-freezing conditions produced less pigment than cool ones. The same paper notes that anthocyanins have become popular in the cannabis industry, partly for their visual appeal.
Why some buds look red, pink or blue
Anthocyanin colour shifts with acidity. The pigments look red in acidic conditions and turn bluer as pH rises, and light, temperature and the pigment's structure also play a part, the Food & Nutrition Research review explains. Shades vary in cannabis too: in the Italian study, accession S1759 ended the season completely red, leaves and flowers included, rather than purple.
Is purple weed stronger?
Not because of its colour. The high comes mainly from THC, which Health Canada says causes the intoxicating and impairing effects of cannabis, while the purple comes from anthocyanins. They are made in different places, too: anthocyanins build up mainly in the outer cell layers of plant tissue, while THC and CBD are made in the resin glands called trichomes, the Wisconsin paper notes. Our guide to trichomes explains those glands.
In that study, the temperatures that produced the most pigment were not the ones that produced the most CBD or the heaviest flowers. CBD and flower weight rose with plant maturity, and the authors concluded that pigment is regulated separately from CBD. The study measured CBD rather than THC, so the reliable way to judge strength is still the THC figure on the label, which can vary from batch to batch.
How to judge purple flower
- Read the THC and CBD on the label rather than going by colour.
- Judge aroma with your nose. Terpenes are responsible for cannabis odours, as a 2022 PLOS ONE analysis notes, and our terpene guide explains what each one smells like.
- Do not assume a purple strain is an indica. Indica and sativa labels match a plant's genetics poorly, according to a 2021 Nature Plants study, as our indica vs sativa guide explains.
- Expect colour to vary between batches of the same strain, since growing conditions such as temperature change how much pigment forms.
Buying purple strains
GasDank offers same-day delivery across Toronto and the GTA, usually within 1 to 2 hours, and mail order across Canada. Browse the flower menu and choose by THC, aroma and type rather than colour alone; the menu carries lab-tested products. In Toronto and Mississauga the minimum order is $40, with free delivery from $80 ($15 below that).
