Why does cannabis change colours?
There are a range of colour-producing chemicals found naturally in cannabis. Normally, the most dominant pigment in cannabis is called chlorophyll.
This has a characteristic green appearance and is present is such high amounts that the other colour-producing chemicals and pigments rarely get chance to display their own hues.
However, when chlorophyll content is reduced (for example during cool bloom conditions) you can see the other pigments and phytochemical display their true colours.
This can allow the leaves and buds to take on striking colours of their own. This can happen towards the end of bloom as chlorophyll content reduces.
It can also be seen if cool bloom conditions are present. Under these circumstances chlorophyll production is reduced allowing other pigments to be seen more clearly.
Cannabis phytochemicals, the chemistry of weed colours
Anthocyanins (From Yellow/Orange to Blue, Black or Even Red)
Anthocyanins are water soluble pigments and are found extensively in nature. Blueberry, raspberry, black rice, and black soybean are just some of many foods which contain these. Interestingly, the precise colour of a particular anthocyanin can vary according to the pH. The striking colours of anthocyanins create some vivid effects. Purple cauliflower strains are rich in anthocyanins as are red radish and black plums. In cannabis, especially in the absence of chlorophyll, anthocyanins can produce some striking colours in the leaves and buds.
Chlorophyll (Green)
Chlorophyll is a natural plant pigment with a Magnesium atom at the centre. Chlorophyll is absolutely essential for photosynthesis. This is the process where light energy is captured by the plant and converted into chemical energy and fuel for growth. Chlorophyll allows the plant to absorb (mainly) blue and red light. Green light is not heavily absorbed by the plant and is reflected, which is why many plants appear green. When chlorophyll levels are slightly reduced from their maximum, other colourful phytochemicals can dominate the colour spectrum.
Carotenoids (Orange, Yellow, and Red)
Carotenoids are organic pigments produced by plants, algae, bacteria and fungi. They are coloured orange, yellow and red. Carotenoids are the pigments that give defining colour to canaries, flamingos, tomatoes, carrots, pumpkins, salmon and lobster. They also help cannabis to produce orange, yellow and red colourations. These can be particularly vivid towards the end of bloom especially when the dense green colour of chlorophyll starts to fade.
Flavonoids (Numerous Colours Including White and Cream)
Flavonoids are naturally made chemicals found in cannabis and a variety of fruits and vegetables. The chemical structure always has 15 Carbon atoms. These water soluble compounds are thought to offer health benefits and antioxidant effects. One sub-group of flavinoids are called anthocyanidins, these are closely related to (but not exactly the same as) anthocyanin pigments.
Cannabis growth stage and temperature levels
Most growers start to look for colour in their buds and plants as harvest approaches. This can be a time when autumnal colours are at their peak. Outdoor cannabis growers will be familiar with the temperatures starting to decrease as autumn/fall gets nearer. Chlorophyll production decreases as temperatures drop. This is one reason why cannabis leaves and buds can take on some gorgeous colours as harvest gets closer.
Some indoor growers also take advantage of this effect and deliberately reduce temperatures, especially during the ‘lights out’ period of indoor cultivation. The result can be quite dramatic and may increase the perceived ‘bag appeal’ and possibly the overall value of the harvest.
Lighting (type, cycle, intensity)
Use of UV lighting towards the end of the bloom cycle can have quite a dramatic effect on the plant colour and pigmentation. UVA/UVB can encourage a mainly ‘green’ plant to adopt some varied coloration. Leaves may darken and show brown/warmer hues to the buds and leaves.
pH levels and nutrient feeding schedule
The pH in the immediate vicinity of certain phytochemicals, e.g. anthocyanins, can dictate the specific colour of it. pH is not fixed in a cannabis plant, it can drift slightly but that can be sufficient to allow subtle differences in shade and colour in different parts of the plant.
Growers carefully control the pH of their nutrients, and it is thought that leaning towards one side of your desired pH range may influence the colours in your plant.
However, many growers might argue that it is preferred to stick in the middle of your nutrient pH range rather than err heavily towards one side of that pH range.
For example, some cannabis growers feel that a more acidic nutrient pH nearer to pH 5.5 will result in more red colours. Conversely, nutrient pH nearer to 7 is thought to produce more blue/purple colours.
A slight Phosphorus deficiency is also thought to produce more red hues. But again, deliberately creating a slight nutrient deficiency to encourage more weed colours would be regarded as an unnecessarily high risk cultivation philosophy to many.
Cannabis seeds genetic heritage
One huge factor which can affect cannabis colour is the type of cannabis seeds you are growing. If the strain was created with the right cannabis genetics you may find that crops of colourful cannabis are easy to produce. Strains like Bubba Island Kush and Auto Blackberry Kush are highly recommended to growers that have a high value for colourful marijuana! It doesn't matter whether you choose autoflowering cannabis seeds or photoperiod feminised seeds, so long as the cannabis genetics are from a reputable breeder you should be in with a good chance of a colourful plant at harvest.
Weed buds colour and potency: myth & facts
The biggest weed bud colour myth is that more colour means more THC. A few decades ago, before THC testing became widespread, people would made ‘educated guesses’ about cannabis potency.
Often their hunch that a particular strain was ‘better’ would be due to an unusual colour or aroma. Today we know that cannabinoids and THC levels are responsible for potency. Weed colour is down to a combination of factors and the presence/absence of natural pigments in the plant cells.
How to enhance your weed bud colours
If your cannabis is good quality with the recreational/medical effects that you want, then you probably aren’t too worried about weed/bud colour. Some commercial growers try to combine high quality THC rich cannabis genetics with a strong bag appeal and good bud colours.
Typically this is done by carefully and steadily introducing low grow room temperatures in the last few weeks of bloom. Often this is done with cannabis strains known for a colourful display. If you haven't tried growing weed/buds with colour then you may want to consider one of the strains suggested above. If you get lucky you could enjoy some of the best-looking buds you have ever seen!
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