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Cannabis Purple Stems

cannabis purple stems

Although cannabis is often green, it is also known for its tendency to generate different colors. You might be shocked to find red or purple stems cannabis plants. You may even begin to be concerned about the plant’s general health. Many growers wonder what do purple stems mean and if they are dangerous. Continue reading to see what causes cannabis purple and red stems and how to avoid them.

Introduction to the Spectrum of Stem Colors in Cannabis Plants

Cannabis is a remarkable plant with the potential to display a wide range of colors. While people typically think of cannabis as a lush green plant, it is usual for some types to acquire purple, pink, and crimson hues, especially in the latter weeks of blooming. As a result, if you notice one of your green plants developing stems with red or purple tints, remain calm and check them more closely. In most circumstances, if a plant seems generally healthy (that is, it is growing well and has lots of healthy leaves), its genetics usually cause red or purple discoloration of the stems. However, suppose a plant develops red or purple stems cannabis and symptoms of stress such as discolored, drooping, or clawed leaves, foliar damage, and stunted growth. In that case, you should look further to determine whether a more serious problem is hidden.

Decoding the Mystery of Purple Stems in Cannabis

When gardeners detect purple stems on weed plants, it generally raises concerns about their health. Plant stem color variations can indicate various environmental conditions, genetic features, or nutritional deficits. In particular, purple indicates a stress reaction, whether from temperature swings, pH imbalances in the soil, or a phosphorus shortage. However, some plants naturally display purple coloration as a typical manifestation of their genetic traits.

Unraveling the Cause of Red Stems in Cannabis Plants

Red stems on weed plants can be caused by one or more issues within. Sometimes it’s nothing and the outcome of something beyond your control. Cannabis red stems may be produced by a variety of factors, including your grow light being too near, nutritional deficits caused by incorrect measurement or PH, temperature modifications, and even your plant’s genetics. Taking extra precautions is critical to ensure you’re applying the proper solutions.

The Botanical Science Behind Purple and Red Stems

The botanical science underlying purple and red cannabis stems is complicated and depends on genetics, light exposure, temperature, nutrition, and infections. Here are the main causes and impacts of cannabis plant stem pigmentation:


Some cannabis strains consist of anthocyanins, natural pigments that give the leaves, flowers, and stems colors (purple, red, blue, or pink). These pigments are often more visible at lower temperatures because they cover up the green chlorophyll that fades in the fall. Purple strains with very dark foliage, for example, typically produce cannabis purple stems.

Exposure to light

When exposed to intense light, cannabis stems may alter color, particularly if the plant has been trained or defoliated to maximize light penetration. The light encourages anthocyanin and other pigment formation in the stem, to protect the weed plant from UV damage and oxidative stress.

Purple cannabis plant
Purple cannabis plant grown indoors

Indoor gardeners who use LEDs or lighting systems with a high UV output are more likely to encounter this occurrence.

Find out the perfect light cycle for cannabis to ensure there are no lighting


Temperature changes can also impact the color of cannabis stems by influencing the activity of enzymes and hormones that govern pigment production. In certain strains, cold temperatures can promote purple or cannabis red stems, while high temperatures can limit anthocyanin synthesis and result in green stems.


Nutrient imbalances or deficiencies can cause stem discoloration, affecting the plant’s metabolism and health. Phosphorus deficiencies are mostly well-known to develop purple stalk weed before the leaves turn brown and brittle. Magnesium deficiencies often cause red petioles, the stalks that attach a leaf to a stem.


Some fungi, like Fusarium or Botrytis, can infect the cannabis stem and cause it to rot or die. Fusarium affects cannabis seedlings, attacking their stems and causing them to “damp off.” It can also make stems appear dark brown, red, or slightly purple. Conversely, Botrytis affects larger cannabis plants and forms a characteristic brown line along the stems and branches affected stems and branches, robbing them of nutrients and causing them to die.

Identifying Purple and Red Stems: A Guide for Cannabis Cultivators

Purple and cannabis red stems in plants can have different causes, depending on the overall health and appearance of the plants. Other times, it is simply an issue of genetics or light exposure, and nothing to be concerned about. If your weed plants also exhibit stress symptoms, such as discolored, drooping, or broken leaves, stunted growth, or mildew, this might suggest a more serious problem.

Treating Purple and Red Stems: Steps for Healthy Cannabis Growth

Treating red stems on weed plants is easy as long as you know what’s causing the issues. Some of the treatment alternatives are:

  1. Give your weed plants good air circulation: Install oscillating fans in the grow tent or tent to give your plants a proper ventilation system. Fans let air circulate, allowing the weed plants to get more oxygen, which is vital for them to continue developing and producing green pigments.
  2. Provide adequate lighting: Insufficient sun or artificial light exposure can cause your cannabis to suffer due to a lack of vitamin D, a primary component of the plant’s photoreceptor cells that causes discoloration. However, you are recommended not to expose your cannabis plants to direct sunlight. In addition, you can put them in a window with better lighting, but away from direct sunlight.
  3. Get rid of pests: Use the best pest control system in your grow area to rid your plants of bugs and pests effectively. You can also purchase eco-friendly pesticides to avoid applying too strong chemicals to your cannabis buds.
  4. Regulate temperature: If your plants have purple stalk weed or red after a cold night, keep an eye on them in the days that follow. You don’t have to worry about your plants’ stems becoming red if they continue to develop properly. You can adjust the temperature in the grow room if you see stunted development or other indicators of cannabis stress. It’s also a good idea to bring your cannabis plants indoors if they’re currently outside.

Understanding the Role of Genetics in Stem Coloration

Plant pigmentation in cannabis is a fascinating trait that is greatly controlled by genetics. Both genetic and environmental factors usually influence the emergence of purple stems on weed plants. Cannabis plant coloration is heavily influenced by genetics. Purple stems are a natural feature of some weed plants, showing a genetic predisposition for this trait. These weed plants inherit the ability to be colored from their parent strains, emphasizing the relevance of genetic composition in shaping plant physical features. Examples of strains with purple or cannabis red stems are:

  1. Blueberry is an Indica-leaning hybrid with a solid genetic foundation. It is a three-way hybrid strain of an Afghani Indica parent and Thai and Purple Thai strain parents. Blueberry is an excellent choice for experienced and beginner gardeners due to its exceptional resistance to pests and stress, rapid blossoming, and big yields of thick, resinous blooms. This Indica plant needs a lot of room since it likes to grow horizontally, making it broad. When growing this cannabis strain outside, feed it the best organic fertilizers to grow quickly into a tall, happy plant.
  2. Purple Haze is a powerful Sativa-leaning hybrid crosses Purple Thai and Haze strains. This weed strain takes care of itself during the growth cycle, which is very useful for novices or those looking for a project that requires little attention. Purple Haze grows well in northern regions but is best planted in a warmer, sunny Mediterranean area for optimal development. Indoors, this plant may thrive in hydroponic systems and properly designed soil. In ideal indoor circumstances, you may anticipate harvesting 350-450g/m2, a decent quantity given the strain’s ease of growing. Purple Haze outdoor yields normally range between 400 and 500g/plant; however, this might vary.

Nutritional Deficiencies and Their Impact on Stem Color

Nutrient deficiencies cause various symptoms, including yellowing or new and old foliage drying, and discolored stems and leaves. In particular, phosphorus is required for proper root development, energy generation, and blooming in cannabis plants. A phosphorus deficit can cause red or purple stems cannabis, as well as indicators such as leaf darkening and curling, diminished blooming, and poor development. To correct phosphorus shortage, ensure your plants receive a suitable fertilizer solution with proper phosphorus levels.

Environmental Factors Contributing to Purple and Red Stems

  1. Watering practices

Overwatering is a major stressor affecting the root zone, causing a lack of oxygen; thus, suffocating and making them more susceptible to diseases. To avoid overwatering your weed plants

  • Ensure your pots have proper drainage.
  • Have a soil moisture meter to gauge water requirements.
  • Allow the soil’s top inch dry out before watering again.
  1. Transplant shock and root distress

Transplant shock occur you disturbing your cannabis plant’s root system when moving them to a new environment. Indicators of shock on your weed plants include wilting, yellowing leaves, and feeble stems. To reduce transplant shock:

  • Handle roots gently during transplantation.
  • Water thoroughly after transplanting your seedlings to help the roots settle.
  • Use rooting hormones to enhance root development and reduce stress
  1. Plant stress

Minor changes in temperature, humidity, lighting, feeding, and watering, as well as advanced training techniques, pests, diseases, and high winds, may all stress cannabis plants, and all of these stressors have the ability to generate red or purple stems. However, defining what stressing a plant is is challenging since each specimen responds differently to stress, and some strains are more resistant to certain forms of stress than others. Here are some common stresses to consider:

  • Pests and illnesses: Certain weed strains are more vulnerable to pests and diseases than others. Apart from purple stems cannabis, check for signs of mildew and bugs, damaged leaves, and stunted development.
  •  Root shock: This is a common issue when transplanting cannabis. If you discover weeds with purple stems after transplanting your plant, give it plenty of TLC to help it recover fast.
  •  Issues with temperature or humidity: Regulate the temperature, and you’ll decrease the stress that creates purple-stemmed plants.
  • Light or heat stress: While cannabis cultivars usually like lots of sunlight, excessive heat can be harmful.

Temperature Fluctuations and Their Effects on Cannabis Stem Color

The principal cause of cannabis purple stems is abrupt temperature changes. An outdoor cannabis plant with a temperature range of 45°F-75°F during the day and night is more likely to develop red or purple stems than one with stable levels. Temperature changes in indoor grow rooms may be caused by your cannabis light cycle. Check that the dark period is not more than 10-15°F colder than the light cycle. Some strains, known as purple strains, are naturally tailored to respond to anthocyanin production. Their leaves and stems take on red or purple tones.

Growers intentionally expose these plants to colder evening temperatures to highlight their beautiful hues. Keep a check on your weed crops for a few days if you observe red or purple stems after being in cooler temperatures. Even more so if they are not from the purple family. If you notice indications of stress, you may need to raise the temperature in your grow room or transfer your plants indoors. Generally, the optimal temperature for producing weed is around 68-77°F during vegging and 65-85°F during blooming.

Exploring the Impact of Light Intensity on Stem Coloration

Lighting is important for cannabis plant health and can affect stem colors. Although not necessarily insufficient or excessive light, exposure to high-intensity illumination might result in purple or red stems on weed plants. This “sun tan” happens as a plant defense mechanism to protect the stems from excessive light, and it is more prevalent with lights that emit a lot of UV radiation. Growers need to select the appropriate light spectrum, change the light intensity, or maintain a regular lighting schedule to achieve optimum lighting:

The Connection Between Cannabis Strains and Stem Colors

Purple stems on weed plants may not always indicate a problem. Some strains generate purple stems on their own. However, if you observe additional indicators of distress in your plants, chances are they lack something or receive an excessive amount of anything. You should ensure you’re giving your weed plants everything they need. Ultimately, you’ll figure out what is incorrect after some troubleshooting.

Picture of Ed Rushford

Ed Rushford

Ed Rushford’s impact on cannabis growing is undeniable. Though he tends to focus primarily on 2 areas, plant training techniques and dealing with disease, pests, and other problems, he has offered many insights into how cannabis plants live and grow. That’s not to say that Ed is unfamiliar with the complete life cycle of cannabis, from seed to harvest, but he uses his widespread knowledge to hone in on the minutia and niche areas of growing cannabis. Ed’s goal is to spread knowledge and allow for everyone to become better growers. About this Author

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