Getting to the Bottom of Why Some of the Most Popular Marijuana Strains Have Bright Purple Leaves

Granddaddy Purple. Purple Urkle. Purple Monkey Balls. Mendocino Purps. Purple Passion. These are just some of the most well-known of the dozens of marijuana strains advertising their violaceous pedigrees. These strains can produce stunning color variations from yellows to blues, and most of all, luscious purple.

Purple pot sure is pretty, but how do those leaves and sometimes even buds acquire those otherworldly aubergine hues? There are a lot of explanations out there, and some are even accurate.

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But first, let's dispose of some urban myths about the mysterious empurpling process. You can't do it by depriving the plants of oxygen or carbon dioxide or otherwise manipulating the atmosphere, and you can't do it by amping up nitrogen levels in the soil. Instead of nice purple leaves, you'll get browned or blackened leaves scorched by fertilizer burn. Nor does manipulating the light cycle, the growth medium or the amount of water achieve purplescence.

It shouldn't really be a surprise that genetics plays the key role, but growing conditions come into play, too. Chlorophyll makes plants green, but a group of molecules called flavonoids (no relation to flavor; the word comes from the Latin for yellow) impacts coloration.

Some marijuana strains contain higher levels of a family of flavonoids called anthocyanins, which produce a purple, red or blue pigment. These same anthocyanins are also found in richly colored plants such as blueberries, red cabbage, eggplant, concord grapes, and violets. When it comes to marijuana, high-anthocyanin strains include not only the various purples, but also strains with blue (Blue Mystic, Bluematic) or red (Red Poison) in the name.

So if you want purple plants or buds, the first thing you do is procure plants with the genetics to lean toward purple. But you also want those color-causing anthocyanins to express themselves. They aren't going to do it until late in the season, as chlorophyll production slows down, and at that point, two factors will influence the purple production: temperature and pH level.

Purple pot needs coolness at night. That's because higher temperatures destroy anthocyanin production. People with a controlled grow environment are advised to set night-time temperatures below 50 degrees; outdoor grows will fare better in a climate with sharp day-night temperature differentials (Nevada, anyone?) than more moderate climes.

The same research that identified the importance of cool nights also identified the role of pH. Neutral pH favors purpling, while higher pH creates more blue, and in more alkaline conditions, yellows. Low pH and acidic environments tend to make anthocyanins express as reds and pinks.

That's how you get purple pot. The anthocyanins don't influence much other than coloration, though. Taste and smell are influenced by terpenes, and the high by THC and other cannabinoid levels, so you can get purps with the whole range of marijuana's flavors and strengths. Happy hunting. 

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