Why Is Some Cannabis Purple?
October 15, 2026
Every so often a jar opens on flower so dark it looks bruised, the bracts gone the color of a ripe plum with orange hairs running through them. People lean in. Purple cannabis has sold on its looks for decades, and in California a name like Granddaddy Purple or Purple Urkle still moves jars off a shelf faster than most of their green neighbors.
We think it is the most overpriced trait in the jar.
The guides that rank highest for this question tell the story the same way: a pigment called anthocyanin, a gene that permits it, cold nights that reveal it, a note about pH, a list of purple cultivars and a reassurance that purple is no stronger than green. We will cover that ground. Then we want to follow the color somewhere none of them go, which is into the resin, because what happens to purple when cannabis is pressed into hash says more about its value than any strain list.
The pigment
Anthocyanins are the pigments that color blueberries and red cabbage. They belong to the flavonoid family, they dissolve in water, and the plant stores them in the sap of its cells. Cannabis makes them for protection, the same reason it makes resin, and the pigments help shield tissue from strong ultraviolet light and from stress.
Their color depends on acidity. In acidic sap anthocyanins lean red; near neutral they sit in the purples; as conditions turn alkaline they drift toward blue. Anyone who boiled red cabbage in a school science class and dropped vinegar into the purple water has watched this happen. It is why purple flower ranges from wine red to something close to navy, and why the same cultivar can show slightly different shades from one grower to the next.
Genetics decide, the weather reveals
A plant without the genetic capacity for heavy anthocyanin will stay green no matter what you do to it.
For the plants that do carry it, the pigment is often present but hidden under chlorophyll for most of the season. Late in flowering, as the plant winds down and chlorophyll breaks down, the purple comes through, much the way a maple shows its red in October once the green has gone. Cold nights speed that up. Outdoors, the long autumn finish does the work on its own, which is why our guide to sun-grown cannabis notes that cool late-season nights bring out purple and burgundy tones that indoor growers have to chase on purpose.
Indoors, chasing it usually means dropping the room temperature at night in the last weeks of flower. Some growers do this gently and well. Others push it hard because a purple jar photographs beautifully, and the plant spends its final weeks reacting to cold instead of finishing its work.
Two lookalikes worth knowing. Purple stems and purple fan leaves on an otherwise green plant can mean nothing at all, since many cultivars color their stems, or they can be a sign of a nutrient problem during the grow. Neither has much to do with the flower you buy. And the hairs on a bud (the pistils) sometimes come in pink or violet, which is a separate trait and looks lovely against green bracts.
Purple and potency
Purple flower is no stronger than green. Potency lives in the cannabinoids, flavor in the terpenes, and both are made in the resin glands we describe in Cannabis Trichomes Explained, which are a different factory from the one making the pigment. One of the top-ranking guides goes the other way and says purple strains run weaker. We do not think the color tells you that either. Some well-known purple lines are modest in THC, plenty of green ones are too, and as we argue in Does THC Percentage Matter? the number was a poor guide to pleasure in the first place.
The grape and berry notes that so many purple cultivars share come from their terpenes and their family tree, which tend to travel together through a breeding line. The pigment itself contributes no aroma you can smell in the jar.
Where the purple goes in hash
The usual guides stop before this. Anthocyanins are water-soluble and sit in the plant’s tissue. The cannabinoids and terpenes are oils, sealed in the heads of the trichomes on the surface. When a hash maker washes fresh frozen flower in ice water and sieves out the resin heads, as described in our guide to solventless rosin, the leaf and bract stay behind in the bag, and the color stays with them.
Wash the darkest Granddaddy Purple you can find and, washed cleanly, the hash comes out pale gold, much like hash from a lime-green plant.
We find this clarifying. Hash makers are the most demanding judges of a cultivar we know, because they pay for exactly one thing, which is the resin, and in their world the purple is simply gone. Whatever a purple flower is worth, its color stays on the surface of the plant.
What the color can tell you at the counter
Not nothing.
Look past the purple for the frost. Dark bracts make a good coat of trichomes easier to see, so a purple bud that still looks dull and matte under the shop light has little resin to show, and the color is doing the selling. It also pays to notice where the purple sits. Color confined to the small sugar leaves around a bud often disappears in a tight hand trim, so an honest grower’s purple cultivar can look greener in the jar than in the photo, and a very leafy purple bud may simply have been trimmed loosely to keep the color.
Ask whether the batch was grown indoors or under the sun. Purple on outdoor flower usually means autumn arrived on schedule. Deep purple on an indoor cultivar not known for it suggests someone turned the room cold, and it is fair to ask how cold, and for how long.
Then open the jar. Purple flower that smells alive and specific, the way we describe in What Makes Cannabis Craft, is good flower that happens to be purple. Purple flower that smells of hay or of very little has been bought for its looks, and the looks were the only thing it had.
Our position
We like purple cannabis. We would not pay a cent more for the color.
If two jars of the same cultivar sit side by side, one deep purple and one green, buy the one with the better nose, and if that turns out to be the purple one, enjoy the plum color as the small bonus it is. Our guide to cannabis phenotypes explains why two plants from the same name can differ so much in the first place, and the guide to terpene profiles will help you put words to what you smell when you get the lid off.