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Blue, red or purple: pigmentation of cannabis plants against the cold

Blue, red or purple: pigmentation of cannabis plants against the cold

Ramón Souto

We have been enjoying different coloured varieties in our gardens for years now: the violet tones of the Purple, the blueish tones of the Blueberrys, reddish buds, Pink Panama pistils…


In ancient times, it was said that purple varieties did not have a strong effect and were instead rather light in terms of the high they produced. These were nothing but urban legends, since in fact there are purple varieties of great power like Grandaddy Purple or Pakistan Chitral Kush.

This type of varieties, when flowering arrives, start to turn their flowers and leaves to an intense purple colour, that can sometimes be almost black.

The anthocyanin name was coined by the German pharmacist Ludwig Clamor Marquart (1804-1881). It happened during a project based in Mendel’s studies of peas, aimed to discover the blue pigment that dyes the red cabbage (Brassica oleracea) in the year 1835.

 Why do cannabis plants change colours? What is the reason behind it?

Certain soluble pigments, called anthocyanins, are responsible for the change of tonality in plants. They can be found in the plant cell vacuoles, and they are very numerous and of different colours (dark red, blueish or purple). Experts have listed up to 400 different individual anthocyanins. Most of them are in berries, the pulp of red fruits and the peels of many fruits.

Anthocyanins are classified in the group of flavonoids (flavus: yellow) of yellow pigmentation and a strong bitter flavour. Flavonoids are a group of natural pigments that have as their main mission to attract pollinators and animals for the purpose of spreading the seeds. Flavonoids were discovered by Robert Doyle in 1664. However, the first flavonoid to be identified was citrine, thanks to Nobel prize winner Szent-György in 1930.

The anthocyanins determine their colour depending of the acidity level (Ph). Ph’s that are above 7 (alkaline) present a blue tinge. When the acidity level stays inside the range of 5 to 7, a purple tonality appears. When we have an acidity level below 5 (acidic condition), reddish tones show.

The temperature parameters can also have a big influence. In some varieties, despite anthocyanins, the striking tonalities will not appear if there is no decrease in temperature. Therefore, we can obtain different colours and effects cultivating the same genetic variety but with different parameters of temperature and Ph.

Anthocyanines do not intervene in the whole cycle of the plant, they just appear during flowering stage. Chlorophyll production decreases and these pigments start to accumulate in certain areas of the plant. This causes the plants to show different tonalities.

What is flavonoids’ mission?

  • Defence against herbivores
  • Protection against ultraviolet rays
  • Attraction of pollinators, therefore perpetuating the species
  • Regulation of cell cycle
  • They play a part in the transport of auxins (hormones that regulate growth)

What properties do flavonoids have?

Flavonoids have antioxidant, anti-inflammatory, anti-allergic, anticarcinogenic, anti-diarrheal, and antibiotic properties, thus having lots of different uses in pharmaceutical industry, such as improving the blood supply. That is why they are recommended for patients with a history of vascular diseases, cholesterol or hypertension.

They protect the capillary vessels present in our eyes. Anthocyanins are a good option for patients with cataract, glaucoma or conjunctivitis. Moreover, there is a possible affinity between anthocyanins and the cannabinoid receptors (CB1 and CB2).

It’s important to remember that the colour of the different varieties is limited by several factors: the genes, the growing conditions, the nutrition table and the weather conditions.

It is crucial to study these genetics. If they truly are so beneficial, they could make an excellent choice for consumers of medical cannabis. Anthocyanins are not an exclusive of cannabis, we can find them in tomato or having a glass of wine.

If we want to force the plant to show those tones, we must reduce the temperature of the crop during the last two weeks. This should be done gradually, in order not to cause stress in the plants. Temperature should be kept between 5 and 10ºC, helping to obtain the colours.

I wish you the best of smokes. You will find us here, cultivating our ideas.

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