How to Grow Purple Cannabis
Every grower has fantasised about harvesting big, purple buds at home. But what exactly can you do to manipulate the colour of your weed?
Purple cannabis certainly does exist, but there’s a right way to turn your pot purple, and a wrong way.
HOW TO GROW PURPLE CANNABIS
Purple weed is real eye candy. And while there are many rumours circulating the internet about how to grow purple cannabis at home, there are really only two variables that you can play with to manipulate the colour of your weed. Keep reading to find out what they are.
WHAT CAUSES CANNABIS TO TURN PURPLE?
All plants have naturally occurring pigments. The most dominant pigment in most plants (including cannabis) is chlorophyll, which, apart from helping plants photosynthesise, also gives them their green colour.
However, plants also have many other active pigments, including carotenoids and anthocyanins. In the absence of chlorophyll, plants may use pigments like anthocyanins to absorb sunlight and photosynthesise. Unlike chlorophyll, anthocyanins naturally absorb all wavelengths from the sun except those in the indigo spectrum, which is what gives plants their purple colour.
Hence, purple cannabis plants (or any purple plant for that matter) get their colour because the dominant pigment in their leaves and flowers are anthocyanins, rather than chlorophyll.
WHAT PARTS OF CANNABIS CAN TURN PURPLE?
There are four main parts of your cannabis plant that can turn purple:
• Pistils: Pistils are the fine hairs that pop out of your buds, letting you know they’re female. Pistils generally start off a creamy white colour and turn orange/red/brown as plants mature. However, it is possible for your plant’s pistils to turn pink or purple, and this colour will remain after you harvest, dry, and cure your buds.
• Calyxes: Calyxes are the small pods that make up your buds. Cannabis flowers are actually made up of hundreds of these small calyxes stacked on top of one another. As the flowers mature, the calyxes open and reveal their pistils, which are designed to catch pollen from male cannabis plants.
• Leaves: The fan and sugar leaves of your cannabis plant can also turn purple. However, they usually won’t have a large effect on the final colour of your buds, as you’ll likely trim away most of the leaves during your post-harvest work.
• Trichomes: Trichomes are the tiny crystals that cover your buds. While they usually start off clear and become opaque and then amber later on, it is possible for them to turn purple, too.
THE WRONG WAYS TO TURN YOUR POT PURPLE
Many people mistakenly believe that the best way to turn cannabis purple is to deprive their plants of oxygen. However, depriving your plants of oxygen, carbon dioxide, or any other gas will not improve your chances of harvesting purple buds. Feeding your plants more nitrogen also won’t change the colour of your plants, at least not unless you overdo it and end up burning them to a crispy shade of brown.
Some growers also use food colouring to dye their plants. And while it might work, we definitely do not recommend trying it. Finally, changing your plant’s light cycle, watering schedule, or grow medium also won’t increase its chances of turning purple, nor will yelling, screaming, or singing to your plants.
THE RIGHT WAYS TO TURN YOUR PLANTS PURPLE
Now that you know how NOT to go about growing purple weed, here are a few pointers to help you maximise your chances of harvesting some eye-catching purple buds this season:
1: START WITH THE RIGHT GENETICS
Genetics are going to have the biggest impact on the final colour of your plants. So, if you’re set on growing purple weed, shop around for purple strains, as they’ll have been specifically bred for their unique colour. Remember that your buds are going to lose some colour after trimming, so opt for strains with the most vibrant purple pigmentation you can find.
Keep reading through to the end of this article for some top recommendations on purple strains to grow at home.
2: ADJUST YOUR TEMPERATURES
While you might be eager to watch your plants turn purple, this will usually only happen once they’ve finished vegetative growth and start flowering. Once your plants have entered their flowering stage, try dropping your nighttime temperatures. Colder temperatures cause chlorophyll to break down and can encourage your plants to produce more anthocyanins. Ideally, you’ll want there to be a difference of 10–15°C between your daytime and nighttime temperatures.
OTHER WAYS TO GROW PURPLE WEED
There are some other ways to manipulate the colour of your plants. Most of these techniques, however, involve depriving your plants of certain nutrients, which, of course, we do not recommend doing. Even if you are able to achieve some purple colouration using these alternative methods, it will likely be to the detriment of quality, flavour, and potency.
GENETICS: THE #1 REASON WEED TURNS PURPLE
Remember, the two main factors affecting the colour of your cannabis plants are genetics and temperature. If you’re really set on growing purple weed, make sure to invest in the right genetics from the get-go.
At Royal Queen Seeds, our expert breeders have bred some killer purple strains. Make sure to check them out and add a splash of colour to your next harvest:
Purple Queen is an almost pure indica variety bred from Hindu Kush and Purple Afghani genetics. She flowers over 9–11 weeks and produces big, purple buds with a uniquely pungent aroma that combines hints of both pine and fuel. Purple Queen also boasts a THC concentration of up to 22% and produces a nice, relaxing body stone that’s perfect for whenever you need to unwind and relax.
Perhaps you've seen brilliant purple bud. Perhaps you've even accidentally grown it. Now, you'd like to do it on purpose. Here is the ultimate guide to making your bud glow with that unique purple hue.
Purple Cannabis: What Makes Some Cannabis Strains Turn Purple?
For many years, the only purple varieties of cannabis were those that had been grown outdoors and subjected to cold conditions. Many strains of cannabis purple to some extent when exposed to cold; now, selective breeding programs have yielded cannabis genetics that are purple even in normal environmental conditions.
What are anthocyanins?
Anthocyanins are a group of around 400 water-soluble pigment molecules that, due to their structure and biosynthesis, are classed as flavonoids. They appear red, purple or blue according to their pH (in acidic pH levels they appear more red, in neutral conditions purple, and in alkaline more blue).
Flavonoids are generally yellow in appearance, hence their name, which is derived from the Latin word for “yellow”, flavus, and does not indicate any association with flavour. In fact, flavonoids are usually extremely bitter, and are generally associated with pigmentation.
Cannabis is what we consider to be a high plant (as in tall, no word-play here). High plants all possess a vascular system consisting of a xylem and phloem, structures that distribute nutrients and water throughout the plant. These high plants contain anthocyanins in all parts of the plant: leaves, flowers, fruits, stems, and even roots.
Depending on the genotype of the cannabis plant, these anthocyanins may be expressed in the latter part of the flowering period, irrespective of environmental conditions. They may also express in cold conditions. But if the plant does not produce enough anthocyanins, it might not affect the appearance of the plant at all.
How do anthocyanins affect plant appearance?
Anthocyanins are not produced throughout the lifetime of the plant, and it is only during the last few weeks of flowering that they begin to alter its appearance. The absence of chlorophyll in the final stages allows the pigments to show through even more distinctly.
As the days shorten and hours of darkness increase, photoperiod-dependent plants are given the signal to cease producing chlorophyll (which is essential for photosynthesis and vegetative growth), so that energy can be focused solely on producing flowers and ultimately fruits. As chlorophyll breaks down and dissipates from the structures of the plant, and anthocyanins begin to accumulate, the plant takes on vivid purple, blue and red hues.
Even cannabis plants that contain low levels of anthocyanins often change colour towards the end of the flowering cycle. Most growers will be familiar with the gold, orange and ochre hues that appear in many strains of cannabis in the weeks prior to harvest—and while yellowing in the vegetative period or in early flowering is usually indicative of disease or deficiency, in the latter stages of flowering, it is entirely natural.
In this case the pigments responsible are carotenoids, a group of around 600 molecules that range in appearance from pale yellow to deep orange-red. As carotenoids are produced throughout the life cycle of the plant, their appearance in the final stages of flowering is a result of chlorophyll production ceasing rather than enhanced production of the pigments.
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Cannabis can turn purple due to cold
Certain strains of cannabis contain anthocyanins but are unaltered in appearance unless subjected to prolonged periods of cold temperatures. The mechanism behind this phenomenon is not fully understood, but there is a clear link between cold and enhanced anthocyanin production, as blood oranges also require a cold period to fully acquire their red colouration.
One study shows that a complex set of genetic circumstances lead to this occurrence: a gene known as Ruby, which is common to all citrus varieties but is not expressed in most, is expressed in blood orange due to the presence of a special section of DNA known as a retrotransposon, which is a mobile genetic element capable of being transcribed as part of several essential genes.
Due to the ability of retrotransposons to become inserted into essential genes and thereby cause mutations and potential non-viability, plants have evolved complex mechanisms to ensure that retrotransposons and similar genetic elements remain inactive. However, these mechanisms may be disrupted in times of stress, such as when exposed to periods of cold.
The above-mentioned study showed that in blood oranges, activation of the retrotransposon triggers expression of the otherwise inactive Ruby gene, and anthocyanin production kicks in. While studies into cold-dependent anthocyanin production in cannabis have not been conducted, it is likely that a similar mechanism is in play.
Are anthocyanins useful, or just attractive?
Anthocyanins are known to be powerful antioxidants and are also thought to possess analgesic, anti-inflammatory and neuroprotective properties. Recent research has demonstrated that certain anthocyanins have some selective affinity for the cannabinoid receptors, with some types binding to the CB1 and others to the CB2 receptors.
While studies are ongoing, it’s too early to say conclusively whether anthocyanins deserve the recent media headlines that label purple foods as ‘superfoods’. Previous research has linked anthocyanins to a wide variety of health claims, including increased longevity, cardiovascular health, cancer prevention and dementia.
Consumption of blood oranges too has been variously associated with improved cardiovascular health, and there are indications that they may assist in preventing obesity even in individuals fed a high-fat diet.
Solving the mystery of why cannabis and other plants produce abundant anthocyanin when cold or stressed could have many potential benefits in medicine and research. Furthermore, if anthocyanins are found to genuinely possess the health benefits they appear to have, purple cannabis could find itself elevated far above its current status of simply being aesthetically pleasing. It could easily become a serious candidate for further investigation.
Many strains of cannabis purple to some extent when exposed to cold. Now, selective breeding programs have yielded cannabis genetics that are purple.