Purple weed: what it is, why it happens and what effects it has

Purple cannabis is a type of cannabis whose buds, leaves or stems take on violet, lilac or purple tones because of anthocyanins, the same natural pigments that colour blueberries. This colour, so striking in Cannabis sativa plants – hemp included – has barely been studied in cannabis, but it has been studied in other plants, and that helps us understand why it appears.

At Cannactiva we work with legal purple genetics, such as Purple Haze CBD; have a look, too, at the rest of our CBD flower, selected for its genetic profile and aroma.

Why is cannabis purple?

The purple colour in cannabis flowers can be caused by the presence of pigments called anthocyanins, the same compounds that give their colour to other purple or dark red flowers, fruits and leaves, such as blueberries. Although all phenotypes – physical traits – have genetic and environmental components, for some cannabis strains growing conditions can have a greater effect on whether the purple colour appears, while for other strains genetic predisposition can have more influence.

What causes the violet colour in plants?

The violet colour in plants is produced by a group of water-soluble organic compounds (they contain carbon) called anthocyanins, which are made by many plants, including gymnosperms (pines) and angiosperms (flowering plants) [1].

The purple colour of cannabis is due to the lilac colour of anthocyanins, a flavonoid also found in blueberries.

Anthocyanins belong to a group of compounds called flavonoids [2], and their main function is to produce violet, blue and red colours in flowers, fruits and leaves. Fruits such as grapes and blueberries have a high anthocyanin content [1].

Find out more about cannabis flavonoids

Types of anthocyanins in plants

The best-known anthocyanins in plants are cyanidin, delphinidin, pelargonidin, peonidin, malvidin and petunidin. The most common is cyanidin, and together with delphinidin it produces the red and violet pigment. Other colours, such as red and orange, are produced by pelargonidin [3]. That said, yellow and orange are also produced by other compounds called carotenoids [4].

Why does the colour change?

The green colour in plants is produced by chlorophyll, a pigment found in chloroplasts, those marvellous organs responsible for photosynthesis. One day I'll tell you about these chloroplasts and their genome.

These colour changes in plants have been linked to senescence, the ageing process, which is why we see plants change colour when autumn arrives [4].

Carotenoids (responsible for the yellow colour) are present throughout the plant's life, but they go unnoticed because of chlorophyll, the green pigment. When chlorophyll starts to break down in autumn, the carotenoids become more noticeable. Anthocyanins, on the other hand, are generally produced in autumn, before the leaves start to fall [4].

Colour changes in plants are partly due to senescence, the ageing process. That's why in autumn we see red, purple, yellow and orange colours in the trees.

How does purple cannabis come about?

But this isn't the case for many strains of our much-loved cannabis. Because, as we well know, purple cannabis exists, which is why we have cannabis strains such as Purple Haze, Purple Urkle and Purple Kush. There are also hemp varieties named after their red and purple colours, such as “Red Petiole” [5].

So I wonder, and maybe you do too: why is there lilac cannabis? Well, there are other plants that are always red/purple, such as mango trees, or ornamental plants like zebrina or begonia. But the reason these other colours exist, beyond senescence, isn't very clear [4].

Want to try a genuinely purple strain?

If seeing these flowers has made you curious, we have two purple cannabis strains in our range: Purple Haze CBD and Grape Ape CBG. Both have violet tones and less than 0.3% THC.

Take a look, too, at the rest of our CBD flower, selected for its genetic profile and aroma.

What makes cannabis change colour?

The violet colour of cannabis is due to anthocyanins. The presence of these compounds in plants can vary depending on soil pH, that is, how acidic or alkaline the ground they are grown in is. In acidic conditions, many of these anthocyanins are red, while in neutral conditions they are purple, and blue in alkaline conditions [3].

The production of some of these anthocyanins depends on changes in temperature, and one hypothesis suggests that red pigments protect the plant from the harmful effects of light at low temperatures [4].

Whether this hypothesis is true or not, I don't know, but I do know that there are several strains of Cannabis sativa that change colour to reds and purples over time, perhaps because of falling temperatures, senescence, or both.

Why does violet cannabis occur?

The production and accumulation of anthocyanins is due to the expression of certain genes and also to epigenetic changes – changes in the phenotype without any change in the DNA sequence – in the plant [6].

Lilac cannabis comes from seeds whose genetics bring about the expression of genes that make anthocyanin production possible, causing the plant to change colour.

So one thing is clear: some cannabis strains, because of their genes, are always purple. Others change colour depending on changes in their environment (factors such as light, temperature or soil pH).

And here come my questions again: does cannabis that is always purple differ in its genes from cannabis that turns purple? Or are they the same genes, expressed differently depending on the environment? As you can see, purple cannabis raises a lot of questions.

What is a fact in biology, as I mentioned above, is that all phenotypes are a product of genes and environment (*nature *vs. nurture). What we don't know is how much of the purple colour in *Cannabis sativa *is down to genes (nature) versus environment (nurture).

Lilac cannabis indoors: light-induced anthocyanins in indoor growing?

Could the lighting in indoor growing affect anthocyanin production in cannabis? It could be a possibility. What's more, it has been found that these changes in light do indeed affect colouring in other plants, such as strawberries [7].

Origin of purple cannabis

Added by Dani · Cannactiva

Purple genetics are believed to come from cold-climate areas of Central Asia, especially the Hindu Kush mountains (Afghanistan and Pakistan). In those environments, low temperatures favoured the build-up of anthocyanins as an adaptive response to cold and UV radiation. Later, breeding programmes in Europe (the Netherlands and Spain) stabilised the trait in modern hybrids.

Best-known purple cannabis strains

Added by Dani · Cannactiva

These are some of the most recognised purple strains:

• Purple Haze — sativa popularised by the Jimi Hendrix song; violet-tinged buds with a sweet, spicy aroma.
• Purple Kush — indica from the Hindu Kush region; deep purple tones and an earthy aroma.
• Granddaddy Purple (GDP) — highly coloured American indica with a fruity, grape-like profile.
• Purple Urkle — deep purple with a sweet, earthy aroma.
• Blueberry — a classic with blue-purple tones and a blueberry aroma.

Most of these classic strains are high in THC. There are CBD-selected versions (THC below 0.3%) that keep the colouring without the psychoactive effect.

What effects does purple cannabis have?

Added by Dani · Cannactiva

The purple colour doesn't determine a plant's effects or potency. The violet tone comes from anthocyanins – pigments with no psychoactive activity – not from THC or CBD. So a strain isn't stronger because it's purple.

What determines the effect is the cannabinoid profile (the ratio of THC to CBD) and the terpene profile. Many purple genetics share terpenes such as myrcene and linalool, associated with relaxing sensations and sweet or floral aromas. In CBD-rich hemp varieties with THC below 0.3% – the ones that are legal in Spain and the EU – the effect is not psychoactive.

Anthocyanins provide antioxidant capacity in the diet, but their contribution when smoked or vaporised is marginal.

Disclaimer: CBD products are not medicines. This information is educational and does not replace the advice of a healthcare professional.

Medical uses of anthocyanins

Anthocyanins are widely used in the medical and health and wellness industries, given their low toxicity, but also because of their many therapeutic possibilities: these compounds are anticarcinogenic, and have uses in neurodegenerative diseases, diabetes and body weight. These uses may be due to the antioxidant properties of anthocyanins [2].

Anthocyanins have therapeutic uses in cardiovascular disease, diabetes and cancer.

Anthocyanins have become popular as dietary supplements, as some studies suggest that compounds in red wine, particularly anthocyanins, may help against heart disease [8].

So there you have it: when you smoke a joint or a chunk of purple cannabis, maybe you're fighting cancer and losing weight too. I doubt it's true, but it does bring a little inner peace.

Purple cannabis flowers… not just on female plants!

Well, here I'd like to share with you some of my beautiful photos of purple cannabis flowers. But, as I'd always been around female plants, I didn't know that males can produce purple flowers too! It was a lovely surprise for me! And they vary a lot in colour.

Cannabis plants with purple stems

And I've also seen plants with purple stems! As I told you before, the Cannabis sativa plant has a huge amount of variation, both in its genome and in its physical appearance (phenotype). For an example of this, see the post on differences and similarities between hemp and marijuana.

Purple CBD strains at Cannactiva

Although most of the purple strains you see in pictures are psychoactive, high-THC strains, at Cannactiva we work with purple cannabis genetics with less than 0.3% THC, legal in Spain. Here is our current selection of strains with violet hints or intense aromatic notes.

Frequently asked questions

Added by Dani · Cannactiva

Why do only the leaves or tips sometimes turn purple, rather than the whole bud?

Because anthocyanin build-up is localised: the areas most exposed to light and cold take on pigment first, and the concentration varies between tissues. That's why it's common to see purple leaves or calyxes on buds that are still green.

Does the purple colour last through drying and curing?

Yes. Once fixed, anthocyanins are fairly stable; slow drying in the dark with controlled humidity helps preserve the tone, while heat and direct light can fade it.

Does the purple colour affect the amount of resin or trichomes?

There's no direct link. Trichomes (cannabinoids and terpenes) and anthocyanins (colour) are separate metabolic pathways: a plant can be very purple and not very resinous, and vice versa.

Why does the same strain turn more purple outdoors than indoors?

Because of the bigger day/night temperature swing and the natural UV radiation outdoors. Indoors you have to create those conditions (lowering night-time temperatures during flowering and using a suitable light spectrum) to get close to the same effect.

Can pH shift the colour towards blue or red instead of purple?

Yes. Anthocyanins are pH-sensitive: more acidic conditions tend towards red and more alkaline ones towards blue, with purple at the values in between. That's why the same plant can show different shades.

Can CBD-rich strains be as purple as THC strains?

Yes. Colour depends on anthocyanin genetics, which is independent of the cannabinoid pathway, so there are CBD chemotypes just as pigmented as any THC-rich strain.