Red leaf stalks and branches

Cannabis plants can develop red leaf stalks and branches due to several factors, which can be both harmless and problematic. There is no need to panic because you can easily fix most of the causes. Should you fail to do so, it often does not greatly affect the final yield of cannabis plants. In this blog we will explain what causes them, what you can do about it and how you can prevent it in the future.We start with the most common causes.

 

• Part 1 : Genetic Traits
• Part 2: Low Temperatures
• Part 3: Nutrient Deficiency
• Part 4: Environmental stress
• Part 5: Fungus or Disease
• Part 6: Normal Growth

 

Part 1 Red leaf stalks and branches: Genetic Traits

Some cannabis strains naturally have a genetic predisposition to develop red or purple pigmentation in their leaf stems and branches. This phenomenon is completely normal and is caused by the presence of anthocyanins, a group of pigments responsible for red, purple and blue hues in plants. Anthocyanins play an important role in the plant’s natural protection against environmental factors such as bright sunlight or cold, but in certain strains they appear even without any stress.

Cannabis strains known for their colorful phenotypes, such as Purple OG Kush, Mimosa Cherry Kush, or Gelato Olandese Autoflower, often have increased production of these pigments. This trait is often more pronounced when the plants are exposed to lower temperatures or specific light spectrum conditions, especially during the late flowering phase. The colorful appearance is then often seen as an attractive feature by growers and consumers.

Red or purple stems caused by genetics do not negatively affect plant health. As long as the leaves remain green and the plant grows normally, there is no cause for concern. In fact, many growers deliberately choose these strains because of their aesthetic value and the unique appearance of the plants.

Although genetic pigmentation does not affect how healthy or potent a plant is, it is often associated with high-quality cannabis, making it popular among enthusiasts. However, it is important to distinguish between genetically determined red stems and pigment changes caused by environmental stress or nutritional deficiencies, as the latter cases do require attention. When in doubt, it may be useful to research the origin of your seeds and the characteristics of your chosen strain.

Part 2 Red leaf stalks and branches: Low Temperatures

One of the most common causes of red or purple stems in cannabis plants is exposure to cold nighttime temperatures, especially when they drop below 15°C. Low temperatures stimulate the production of anthocyanins, natural pigments responsible for red, purple and sometimes even blue colors in plants. This process is often observed in autumn, when many plants exhibit these colors in response to falling temperatures.

In cannabis plants, this color change is a natural response to the cold and serves as a strain of protective mechanism. The anthocyanins help the plant use light energy more efficiently and provide protection against potential damage from cold. Although the appearance of these red or purple colors is often a sign of stress, it is not necessarily harmful to the plant. If the rest of the plant is healthy, with green leaves and normal growth, this may simply be a visual indication of environmental conditions.

Growers who deliberately apply cold night temperatures sometimes do this to stimulate pigmentation, especially in strains known for their vibrant colors. This can increase the aesthetic value and appeal of the buds, which is popular with consumers.

However, it is important to note that prolonged exposure to very low temperatures can eventually weaken the plant. Cold stress can lead to slower growth, reduced nutrient uptake, and a lower end result. Therefore, ensure stable temperature control, where night temperatures do not drop too far. This minimizes stress and keeps the plant in optimal health while still allowing you to enjoy the visual benefits of natural pigmentation.

Part 3 Red leaf stalks and branches: Nutrient Deficiency

A common cause of red stems in cannabis plants is a deficiency in essential nutrients, especially phosphorus (P). Phosphorus plays a crucial role in plant growth and development, especially in the formation of flowers and roots. When the plant does not absorb enough phosphorus, it can cause red or purple discoloration of the stems and branches.

This problem often occurs under the following conditions:

1. Improper pH of the soil or nutrient solution.
   • Phosphorus availability is greatly affected by the pH of the soil or growing medium. If the pH is outside the optimal range (6.0-7.0 for soil and 5.5-6.5 for hydroponics), phosphorus uptake is hindered even if it is present in the nutrient. As a result, the plant may show symptoms of deficiency, including discoloration of the stems.
2. High phosphorus requirements in the flowering phase
   • During the flowering phase, the plant has an increased need for phosphorus. This mineral is essential for energy transfer and flower development. If the nutrient solution does not contain enough phosphorus to meet this increased need, red stems may develop.

How do you fix this?

• Check pH: Use a reliable pH meter to measure the acidity of your soil or nutrient solution and adjust it as needed. For soil, you can use lime or sulfur to correct the pH, while in hydroponics you can apply a pH-up or pH-down solution.
• Adjust nutrition: Make sure your plants get a balanced nutrition with adequate phosphorus, especially during the flowering phase. Use nutrients specifically designed for cannabis to avoid deficiencies. Giving extra PK 13/14 is the most common solution to this problem and also stimulates the flowering of your cannabis plants.
• Read more about PK13/14 here: PK13/14 blog
• Monitor the plant: If red stems are accompanied by other signs of phosphorus deficiency, such as dark or purple discoloration at the edges of the leaves, it is essential to intervene quickly.

By maintaining proper pH and nutrition, you can prevent red stems due to deficiency and optimize the health and yield of your plants.

Part 4 Red leaf stalks and branches: Environmental stress

Environmental stress is a common cause of red stems in cannabis plants. Two main forms of stress that can cause this problem are excessive light intensity and heat stress. Both factors affect the health of the plant and can lead to changes in stem pigmentation.

Light intensity

Excessive light, or a grow light hanging too close to the plant, can turn the stems and branches red. This happens especially with the new generations of LED grow lights, which emit high intensity in specific spectrums. Although LED lights are more efficient than traditional HPS lights, they can cause stress if used incorrectly. Stress occurs as the plant tries to process too much energy, leading to increased pigment production in the stems as a protective mechanism.

How to solve this.

• Increase light intensity gradually: Build up the light intensity slowly, giving the plant time to adjust. Start at 50% with a lamp distance appropriate for the plant’s life stage (for example, 60-90 cm for young plants, depending on the lamp).
• Check the distance: Make sure that the lamp does not hang too close to the buds. The recommended distance depends on the wattage and type of lamp, but a distance of 30-50 cm is often ideal.
• Read more about ideal LED lights intensity here: Optimal LED Light Intensity for Growing Cannabis

Heat stress

Extremely hot or dry conditions can also contribute to red stems. High temperatures, especially when combined with low humidity, cause stress to the plant. This can lead to increased production of anthocyanins in the stems and twigs.

How do you solve this?

• Manage the temperature: Keep the temperature in the grow room under control. Ideally, the day temperature should be between 21-28°C and the night temperature should not be much lower than 18°C.
• Regulate humidity: A relative humidity of 40-70%, depending on the growth stage, helps the plant avoid stress.

By optimizing the environment, you can minimize stress and reduce the likelihood of red stems. Regular monitoring and adjustments ensure a healthy plant that grows optimally.

Part 5: Fungus or Disease

Although less common, red stems on cannabis plants can be an indication of an underlying infection or disease. This type of discoloration is usually caused by stress at the cellular level, which can occur when the plant is affected by mold or other pathogens. It is important to inspect the plants thoroughly to detect and address possible health problems early.

Possible causes

1. Fungal infections
   • Pathogens such as Botrytis (bud rot) or fusarium can seriously affect plant health. Although fungi are often first visible on leaves or buds, the infection can spread to the stems and weaken them, sometimes accompanied by redness or purple tones.
2. Bacterial infections.
   • Less common, but bacteria can also cause stem discoloration. This can manifest as a soft, rotting texture along with redness.
3. Vascular diseases
   • Some diseases block the transport channels in the plant, preventing nutrients and water from reaching the leaves and flowers properly. This can cause discoloration in the stems as a symptom of the underlying damage.

What can you do about this?

• Remove infected parts: If you see signs of mold or disease, remove the affected parts immediately to prevent further spread.
• Improve air circulation: Ensure adequate ventilation in the grow room to minimize humid conditions. High humidity promotes mold growth.
• Use a biological fungicide: If mold is the cause, a biological or chemical fungicide can help control the infection. Use only as directed on the product label.
• Sterilize equipment: Prevent reinfection by properly cleaning tools, pots and surfaces.

Although fungus or disease as a cause of red stems is rare, timely intervention can save the plant and limit further damage. Monitor the growing environment carefully and stay alert for signs of trouble.

Part 6 Red stems and branches: Normal Growth

In some cases, red stems and branches can be a completely normal part of cannabis plant growth. This often happens without any stress or problems. As long as the rest of the plant shows healthy signs, such as green leaves, firm stems, and a good growth rate, there is usually no cause for concern.

Causes of normal red stems

1. Natural variation
   • Just as some cannabis strains are genetically programmed to develop colorful phenotypes, slight redness in the stems can be a natural characteristic of the strain. This is especially true of hybrids with rich genetic backgrounds.
2. Hormonal changes
   • During the transition between growth phases, such as from the vegetative to flowering phase, hormonal shifts can occur in the plant. This can temporarily result in color changes in the stems and branches.
3. Environmental influences
   • Even under optimal conditions, subtle changes in temperature, light intensity or humidity can contribute to a red hue in the stems without affecting the health of the plant.

How do you know it’s normal?

• Healthy leaves: The leaves remain green, firm and show no signs of yellowing, wilting or other problems.
• Vigorous growth: The plant continues to grow and develop new leaves and buds without slowing down or deforming.
• No other stress signals: There are no other symptoms, such as withered branches, limp stems, or slow development.

Conclusion

Red stems resulting from normal growth are no cause for concern and do not require specific action. If the plant is otherwise performing well, this may simply be a visual feature that contributes to the unique appearance of your cannabis plant. Continue to inspect your plants regularly to ensure no other signs of stress or disease are developing, but trust that a healthy plant will continue to develop as expected.

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