purple kush cannabis

Purple Weed: How Cannabis Strains Change Colors

Who doesn’t love to see their weed plants change from green into the prettiest colours? Purple weed is a beautiful and widely known phenomenon, thanks to iconic cannabis strains as Purple Haze. But why do some cannabis plants turn purple while most others do not? Let’s find out!

Green And Purple: Cannabis Colours

We can see the dazzling colours of the plant kingdom because light reflects on the various pigments plants contain. Sunlight contains all colours of the spectrum, and our eyes are able to up a part of that spectrum. When light hits a surface that ‘has’ a certain colour, say, green, the green part of the spectrum is reflected off the surface. The other colours of the spectrum are absorbed. A green cannabis leaf, then, absorbs all colours except green, and then reflects that green light onto our retina. If a cannabis plant somehow managed to reflect another part of the spectrum, we would see a different colour. That is what happens with purple cannabis plants. As it turns out, these ‘purple’ strains have different compounds in their cells, caused by external factors like temperature, and by genetics.

flavonoids colour

Most plants, including weed plants, are green. The pigment that makes cannabis green is pretty well known: chlorophyll. Apart from the visual aspect, this pigment is recognizable by a bitter taste – found in cheaper CBD Oils for example. Chlorophyll also conveys an acrid, unpleasant taste to cannabis if smoked; this is why growers trim excess leaf material and ‘sugar leaves’ from their harvest before consumption. This green plant colourant is the same substance that gives lettuce and other vegetables their green colour. Anyone with a varied vegetable diet eats plenty of chlorophyll every month, although human metabolism doesn’t do much with this substance.

Green Leaves, Chlorophyll, And Photosynthesis

For plants, though, chlorophyll is absolutely vital. Photosynthesis would be impossible without chlorophyll in the leaves of (cannabis) plants. In photosynthesis, sunlight is converted into energy ready for use in plant growth, development, and flowering. The green leaves of our weed plants are like the solar panels of the species, and so, if cannabis weren’t green, it could never grow in the first place.

Okay, so weed plants need to be green in order to get energy and grow. Then why are some strains purple? Interestingly, purple cannabis derives its colour from another plant compound than chlorophyll. The substance that makes weed plants turn purple is called anthocyanin. Anthocyanins form a group of around 400 water-soluble pigments, belonging to the ‘flavonoids‘ category of plant compounds. After cannabinoids (like THC and CBD) and terpenes, flavonoids are one of the most important components that make cannabis such a versatile, unique, and much-loved plant species.

Purple Cannabis

Anthocyanins do not always manifest themselves in purple hues, though. Depending on the acidity of the plant, this pigment can show different colours. In acid environments these anthocyanins turn red or pinkish. More neutral acidity levels make anthocyanins appear purple, whereas alkaline environments make this pigment turn blue.

purple cannabis anthocyanin
The green’s purple: anthocyanins make cannabis buds turn purple

The word ‘anthocyanin’ comes from Greece. German botanist Ludwig Marquart first discovered the pigment in 1835. He named it after anthos (flower) and kyanos (blue). Although this doesn’t mean the purple in cannabis only shows on the flowers of the plant. Even the leaves, stems and branches can show the beautiful colours of anthocyanin. But what exactly triggers a cannabis plant to turn pink, blue, or purple?

Cold Nights & Genetics

The most important element underpinning this phenomenon is genetics. Some cannabis strains simply produce more anthocyanins than others, though these colours are not always visible throughout the plant’s lifecycle. Nor are they guaranteed to appear in strains like Purple Haze, Blueberry or Purple #1 when you grow them at home. As any experienced grower will confirm, these strains can also grow into beautiful green specimens.

purple cannabis weed buds color
Anthocyanins become more prominent when cold nights make chlorophyll break down into sugars for cannabinoid production

That is because the dominant pigment chlorophyll usually makes it difficult for anthocyanins to show. But as soon as the days turn colder, the cannabis plant starts turning chlorophyll into sugars. These sugars can be used by the plant as energy for the production of flowers, cannabinoids and seeds. This breakdown process gives anthocyanin the chance to push through and really show its true colours.

We at Amsterdam Genetics do not stock these extremely purple colouring cannabis strains like Purple Haze. That is because we select for genetic excellence rather than for any specific colour or other outward trait. We do have some strains that are more probable to turn into purple cannabis plants than others, though. Our Blue Magic and Blue Amnesia for example are strains that are known to turn blueish under the right conditions. For more red / purple like tones, you’d be best off with our Kosher Tangie Kush.

blue magic bud
Our ‘Blue Magic’ is known to turn blueish / purple under the right conditions

Grow Purple Weed

So if you’re planning to grow your own purple weed, the right genetics are a good place to start. Though it’s not all you need to grow colourful weed. As we’ve stated before, an important factor in this color change is temperature. When cannabis plants turn cold, the production of chlorophyll stops; giving anthocyanins room to show their shades.

To all probability, this phenomenon is a survival mechanism for cannabis plants. Whether it is to attract useful insects, or to attract more warmth with their dark colour: WE LOVE IT! Don’t be shy and turn the heat down in the last weeks of the flowering stage to enjoy this spectacle in your own grow room or garden!

purple weed strains cannabis colors


Purple Cannabis And Blue Monkeys

Our dedicated CBD strain Blue Monkey can also turn purple, or even turn almost black, if she’s grown in the right conditions. She’s showing her true colours! This strain is very well-suited for medical use, as she contains 11.4% CBD and 0.03% THC.


Regardless of which strain you prefer, there’s always a chance that a grow turns purple, blue, or another spectacular colour due to anthocyanins. No matter your favourite colour, though, you’ll find all the top quality seeds you need in our AG Strains Catalogue!