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.
Problem: A cannabis phosphorus deficiency generally appears on leaves from the lower/older parts of the plant. The lower leaves may turn dark green or yellow, and start getting spots or big splotches that look brown, bronze or even a little blue. The leaves may thicken and curl, and the affected leaves feel stiff. Sometimes the stems of the plant turn bright red or purple, but not always.
Sometimes accompanied by a Calcium deficiency, as Phosphorus and Calcium interact with each other in the plant.
A cannabis phosphorus deficiency usually appears with some or all of the following symptoms:
- tends to affect the lower and older leaves of the plant
- sometimes a phosphorus deficiency is accompanied by bright red stems (though not always), though if you have red stems but no other symptoms, it’s typically not something to worry about
- leaves darken (turning a dark green, blue or grayish color) and may appear shiny
- leaves may start turning yellow in places if the phosphorus deficiency is left untreated, or if the deficiency is combined with other nutrients deficiencies and/or pH problems. However, yellow leaves is typically not associated with the beginning of a phosphorus deficiency.
- leaves get bronze, purple or brown spots and splotches
- leaves thicken and may feel dry or stiff
- stems sometimes turn bright red or purple, but not always
- sometimes accompanied by a Calcium deficiency, as Phosphorus and Calcium interact with each other inside the plant
- this deficiency is more common after buds start forming, when the plant is using a lot of Phosphorus
Phosphorus deficiencies in the vegetative stage usually appear at the bottom of the plant on some of the oldest leaves, and will progressively climb up the plant if left unchecked.
The progression of a cannabis phosphorus deficiency
A phosphorus deficiency tends to be more common after plants start making buds in the flowering stage. Cannabis plants tend to love phosphorus in the flowering/budding stage and it is unlikely for a cannabis plant to get too much phosphorus using standard nutrients formulated for a flowering plant like cannabis. Nearly all flowering nutrients will come with an abundance of phosphorus for your plants. So if you’re seeing a cannabis phosphorus deficiency while using standard cannabis nutrients, chances are you actually have a root pH problem (explained below in the solution section)!
Phosphorus (P) is used by your cannabis plant in all phases of growth. It is one of the 3 major nutrients (N-P-K) listed on the front of most nutrient bottles, and phosphorus will be represented by the second number that appears.
When there is a phosphorus deficiency, the lower (oldest) leaves turn dark green. Leaves occasionally get a bluish or bronze tinge, and may thicken or curl downward before exhibiting dark gray, bronze or purplish splotches. Sometimes the stems of the affected leaves will turn bright red or purplish, usually starting from underneath.
It’s common to see a Phosphorus deficiency accompanied by the symptoms of a Calcium deficiency, as those nutrients interact with each other in the plant.
Sometimes you will get a cannabis phosphorus deficiency, and the stems do not appear red or purple at all, or the coloring may not be pronounced.
The leaf below was at the bottom of the plant and turned dark green and shiny, with a bluish tinge. Cannabis phosphorus deficiencies usually appear on the lower/older parts of the plant. The leaf then started showing the spots of a phosphorus deficiency where it was being touched by light (the parts of the leaf working hardest). The leaf began to curl downwards and turn yellow.
Notice that the stems or veins never turned red or purple on this leaf, except for some parts that were actually affected by the phosphorus deficiency.
A common symptom of a cannabis phosphorus deficiency is bright red or purple stems, though it doesn’t appear on all affected plants. Red stems can also be caused by direct light exposure (like a “tan”)
Another example of bright red stems that may be the result of a Phosphorus deficiency, or possibly direct light exposure.
It’s important to remember that some cannabis strains naturally grow with red or purple stems even when all their nutrient needs are being fulfilled, so red or purple stems is not a symptom to worry about on its own.
Do not mistake natural reddish-purple colored stems for a phosphorous deficiency!
When you notice that stems are turning red or purple starting from underneath, it may be a sign of a phosphorus deficiency only if accompanied by other symptoms. If the only symptom shown by your plant is red or purple stems, and you are not seeing any other signs of splotches or unhealthy leaves, the red or purple stems are likely caused by the genetics of your plant. If that’s the case, you have nothing to worry about.
Phosphorus is used heavily by cannabis plants in the flowering phase to produce buds, and is a crucial component of photosynthesis (turning light into energy for the plant).
Some strains of cannabis use much more phosphorus than others, or be more susceptible to a phosphorus deficiency, and you may have many plants in the exact same setup with only some of the plants showing signs of a phosphorus deficiency.
Solution For Cannabis Phosphorus Deficiency
1.) Adjust pH to Correct Range
Your cannabis plant may show signs of a phosphorus deficiency if the pH at the roots is not in the right range. That is because when the pH of your root zone is off, your cannabis cannot properly absorb phosphorus through its roots. Therefore the first step is to ensure that you have the correct pH for your growth medium. Learn more about pH and cannabis.
Phosphorus is best absorbed by cannabis in soil at a root pH of 6.2 – 7.0. Phosphorus is best absorbed by cannabis in hydro at a root pH of 5.5 – 6.2. If you believe you have a cannabis phosphorus deficiency, it’s important to check the pH of your root zone to make sure the deficiency isn’t caused by the pH being too high or too low.
If you suspect your growing cannabis plant has a phosphorus deficiency, flush your system with clean, pH’d water that contains a regular dose of cannabis-friendly nutrients that includes phosphorus. This will remove any nutrient salts that may be affected the uptake of phosphorus and help restore pH to the proper levels.
- In soil, phosphorus is best absorbed by the roots in the 6.2 – 7.0 pH range (in soil, it’s generally recommended to keep the pH between 6.0 – 7.0, but phosphorus specifically tends to be best absorbed above 6.2 and below 7.0)
- In hydro, phosphorus is best absorbed by the roots in the 5.5 – 6.2 pH range (in hydro, it’s generally recommended to keep the pH between 5.5 – 6.5, but phosphorus specifically tends to be best absorbed below 6.2)
2.) Take Good Care of the Roots
Wet, compact soil or overwatering can trigger a phosphorus deficiency to appear even when all other factors are perfect. So make sure you water your plants properly every time to help prevent a phosphorus deficiency.
3.) Provide the Right Temperature
Cooler temperatures lower than 60°F (15°C), as well as large temperature swings, can make it harder for the plant to absorb phosphorus. Cannabis plants are therefore more likely to show signs of a phosphorus deficiency when the temperature drops too low, or if they go through a cold spell.
Cannabis likes a comfortable room temperature (they like about the same temperatures as we do).
4.) Give the Right Nutrients
Most growers have actually already given plenty of phophorus to their cannabis plants since it is found abundantly in quality soil and cannabis-friendly nutrients. However, even if you are giving phosphorus, it’s important to give your cannabis the right ratio of nutrients.
An excess of Fe and Zn may cause the symptoms of a phosphorus deficiency by preventing the plant from being able to absorb phosphorus properly. If you believe there may be a buildup of nutrient salts in your growing medium (or if you are growing in hydro and have not recently flushed or changed your reservoir) you should make sure it’s not an excess of other nutrients that is actually causing the phosphorus deficiency to appear. Flush your plant thoroughly with properly pH’ed water containing a regular dose of cannabis nutrients including phosphorus, or completely change your reservoir if you believe that an excess of nutrient salts may be causing the phosphorus deficiency.
Sources of phosphorus:
If you’ve tried everything else, then you may try adding a higher percentage of phosphorus to your feeding schedule and see if that helps clear up the problem for your plant. Cannabis plants love phosphorus, and therefore it is unlikely that you will give your cannabis too much phosphorus.
Most nutrient systems that are formulated for a plant like cannabis will carry and abundance of phosphorus, especially in budding/flowering formulas, so it is unlikely that you will see signs of a phosphorus deficiency before other nutrient problems when using nutrient systems formulated for cannabis (as long as you keep your root pH in the correct range and prevent the plants from getting cold or being overwatered). If you’ve got very high powered lights, or if your plants are growing in direct sunlight, they may be going through a lot more phosphorus in the flowering stage than average and may need you to provide extra phosphorus to make sure buds get as big as they could be.
Just remember that if there’s no actual phosphorus deficiency currently appearing on your cannabis plant, adding more phosphorus is probbaly not going to help plants grow better or make bigger buds – in fact adding too much phosphorus may actually hurt your plants by preventing the uptake of other nutrients! While it’s difficult to overdose your plants on phosphorus, adding too much compared to other nutrients will often cause other strange & unexpected deficiencies to appear.
5.) Take Good Care of the Roots
Phosphorus deficiencies can show up with the plant is having root problems or if the plant is overwatered, even if the pH is right and the phosphorus is there. Proper watering practices help plants grow healthy and avoid a host of problems!
6.) Watch for Recovery
After going through all the above steps, watch to make sure that the phosphorus deficiency starts to clear up within a few days to a week or so. After a phosphorus deficiency is cleared up, the problem (brown spots, unhealthy lower leaves, red/purple stems, etc) will stop appearing on new leaves, usually within a week.
Please note that leaves which have been damaged by a phosphorus deficiency will probably never recover or turn green, so you want to pay attention to other leaves for signs of recovery.
If you cannot get rid of your phosphorus deficiency, please consult our 7-Step Cure to 99% of Cannabis Growing Problems
- Bronze or brown patches
- Brown or slimy roots
- Brown or yellow leaf tips/edges
- Buds dying
- Buds look odd
- Bugs are visible
- Curling or clawing leaves
- Dark leaves
- Drooping plant
- Holes in leaves
- Mold or powder
- Pink or purple on leaves
- Red stems
- Shiny or smooth leaves
- Spots or markings
- Twisted growth
- Wilting leaves
- Yellow between leaf veins
- Yellow leaves
This page is part of our Plant Doctor series. You can use our tool to filter by symptom and help diagnose your plant.
Phosphorus deficiencies cause dark splotches on leaves and can appear at the bottom of the plant on some of the oldest leaves. Learn to spot & fix the issue.