by Nebula Haze
“Could you do a grow piece on the Autumn Color Effect? I saw it crop up a lot on my cannabis plants this winter. I’d love to hear your take, Neb!”
~RunWithIt
The Autumn Color Effect made these cannabis leaves turn bright purple.
Thanks to grower RunWithIt and his captivating purple marijuana plant above for inspiring this Autumn Color Effect cannabis tutorial.
Cannabis plants can be full of surprises. For example, did you know you can sometimes change the color of your cannabis plant leaves and buds to be more pink, purple, or red? Some cannabis strains will always grow pink or purple buds, but many strains only turn colors in certain situations. For these strains, you can induce more colors by stimulating the Autumn Color Effect.
Why do cannabis growers try to promote the Autumn Color Effect?
- Pretty Colors – Vibrant colors is what draws many cannabis growers to the Autumn Color Effect. I think most growers agree that looks probably shouldn’t matter, and the goal is to harvest buds with your desired effects. Yet colorful plants are beautiful to look at and we spend a lot of time with them. You might think, “If I’m going to grow great weed, why not make it pretty?”
- Smooth to Smoke – Part of inducing colors is lowering nutrient levels at the end of the flowering stage. That tactic also helps remove excess fertilizer that might be stored in the plant tissue. That means in some cases, cannabis plants showing the Autumn Color Effect may be smoother to smoke.
- Maximize Potency – To achieve Autumn Colors, cannabis plants typically need strong light on buds during the day, and cool temperatures at night. These factors also tend to produce higher THC levels compared to a plant grown without those conditions. So even if you don’t care about the color of your buds, the following steps maximize bud potency, too.
Now that you know a little about why cannabis growers try to induce the cannabis Autumn Color Effect, let’s look at how to do it.
Forbidden Fruit and Platinum Cookies are two strains that turn a variety of colors in the right conditions.
How to bring out the cannabis Autumn Color Effect
- Choose a Colorful Strain – Some cannabis strains naturally put out purple colors as harvest approaches, like Forbidden Fruit, Purple Ghost Candy or Platinum Cookies. Some strains grow mostly green leaves but vibrant purple buds like Purple Lemonade Auto (an autoflowering strain) or Kushberry Moonrocks. Learn more below.
- Hot Days, Cool Nights – Cannabis plants are more likely to show autumn colors like purple, pink, or red when they experience warm days with cold nights (temperature fluctuations between dark and light periods).
- Strong, Direct Light – High light levels helps induce colors, especially purple. You’ll notice the parts of the plant closest to the grow light are often the most colorful. Of all the types of cannabis grow lights, powerful LEDs tend to bring out colors the best. However, colors also come out under CMH/LEC and HPS grow lights as long as you keep them the right distance and night temperatures are controlled.
- Dwindling Nutrients – Vibrant colors are most likely to appear when a cannabis plant begins to experience nutrient deficiencies. For example, you may see colors appear after a plant has used up most of the nutrients in the soil. Now, it’s important that cannabis growers avoid nutrient deficiencies for almost all of the flowering stage, so that buds form with maximize yields and potency. However, that directive changes in the last week before harvest. At this point, many growers reduce and then fully stop adding nutrients, and give plain water instead. This gives cannabis plants a chance to use up extra nutrients contained in the plant tissue before harvest. As a bonus, this tends to help bring out the Autumn colors.
- Harvest at the Right Time – Colors tend to come out towards the end of the flowering stage, but many growers unintentionally harvest too early. Knowing when to harvest cannabis gives multiple benefits. It not only increases the chance of vibrant colors, but also improves your yield and THC levels.
Combine all these factors for a wildly colorful cannabis garden at harvest time. Bright colors are most likely to happen when you achieve all the factors on the list.
Cannabis plants can experience a colorful stage just before harvest, just like some trees turn pretty colors in Autumn.
Where I grew up, the leaves of maple trees usually turn beautiful colors in the Autumn. However, some years had brighter colors than others, which I learned was based on the weather that year. Also, some individual trees naturally turn brighter colors than others due to their genetics. I remember a specific tree in my yard always turned so red it looked on fire, and none of the other trees could match its colorful splendor. Cannabis plants are the exact same way. A combination of environmental conditions and the right strain brings out the most vibrant colors.
Outdoors, cannabis plants often exhibit similar tendencies in the fall.
Indoors, this “Autumn Color Effect” can sometimes be induced on purpose.
Some cannabis strains tend to become pink, red, or purple, while other strains may only turn yellow or gold.
The Autumn Color Effect most strongly affects the leaves. If you look closely, the buds themselves often stay mostly green.
Strong, direct light can induce colors. One of the best ways to see this is when a leaf is partially covered by another leaf for a long period of time. For example, this leave was partly exposed to the light, and part was hidden by other leaves. You can see the parts that got light turned purple, while the hidden parts of the leave stayed green.
Cannabis leaves tend to turn colors like purple where they get strong, direct light. Kind of like a sun tan. This leaf has tan lines!
Some marijuana strains always turn purple or pink no matter what you do, like Purple Lemonade Auto (an autoflowering strain) or Kushberry Moonrocks. However, following the steps to induce the Autumn Color Effect may deepen and enhance their colorful hues even further.
Some strains like Purple Lemonade Auto always turns purple no matter what.
For some cannabis strains, the effect may be small. Sometimes the only bright color that comes out is yellow. For this next harvest, only one plant showed any purple even though all plants were given the same Autumn Harvest Effect environmental conditions.
Three cannabis strains grown in the same conditions, but only the middle Peyote Critical plant turned purple.
However, the cool thing is the same conditions that tend to bring out colors also can increase the overall quality, potency, and smoothness of buds. So even if you aren’t rewarded with lots of colors, you will be rewarded with excellent bud quality.
I love all colors of weed, including “boring” green and orange buds, but there is something special about seeing a mix of different colors in your garden. These are flowers we’re growing after all!
Summary: The Autumn Color Effect in Growing Cannabis Plants
The Autumn Color Effect is a fancy way to describe when cannabis plants turn bright and pretty colors close to harvest time. Some strategies can be used to increase the chance of seeing colors, including choosing the right strain, giving hot days and cool nights, providing very strong light, and reducing nutrient levels in the last week before harvest.
It’s very important to avoid inducing colors too early. Try to keep your leaves green and avoid nutrient deficiencies until right before harvest time to maximize bud yields and potency. However, if you follow the instructions in this article for the last week before harvest, you can actually increase your yields and bud potency. That means even if you don’t get bright colors, you still improve your overall bud quality by following the simple steps.
Just remember, in the end we’re growing buds for effects, and colors are just a fun bonus. If your buds produce the effects you want, I personally believe you have grown the best buds!
Happy growing!
Nebula Haze
About the Author: Nebula Haze
Nebula Haze co-founded GrowWeedEasy.com in 2010 and has since dedicated her life to teaching growers around the world how to grow cannabis at home. Please use the Search bar to get answers to your grow questions as GrowWeedEasy.com contains hundreds of grow tutorials that cover every aspect of growing at home.
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