My cannabis stems are turning purple and red. Is this genetics or is there something wrong with them?

When first encountered, red and/or purple stems may be concerning, however, there are actually many reasons this pigmentation can occur and not all are bad. The most common reasons for red or purple stems are genetics, temperature fluctuations, light intensity, and stress.

Reason #1: Red or Purple Weed Genetics

When red or purple stems are due to genetics, the plant will otherwise perform and appear healthy. Put another way, if the plant is showing no other signs of distress, the pigmentation could simply be part of the plant’s genetic make-up. There are a wide variety of cannabis genetics in circulation and many of these varieties can produce purple or red pigmentation. (Learn more about purple weed.)

Reason #2: Temperature Fluctuations in the Grow Space

Red and/or purple stems can also appear after large temperature fluctuations. For example, a cannabis plant grown outdoors with a daytime temperature of 80°F and a nighttime temperature of 50°F, may produce red or purple stems due to the abrupt fluctuation in temperature. If an indoor grower is experiencing red or purple stems due to temperature fluctuations, he or she may need to adjust the temperature of the dark cycle so it does not get more than 10-15 degrees cooler than the lights-on cycle. Recurring temperature fluctuation in an indoor garden can eventually lead to more serious humidity related issues.

Reason #3: Grow Light Intensity

Light intensity is another reason a cannabis plant may display red or purple stems. When a stem is exposed to direct, intense light, it may develop red or purple pigmentation. If light intensity is the cause, the stems that are lower on the plant (farther from the light source) will usually appear greener. The coloration under intense light is a natural plant defense mechanism that provides the plant further protection from UV light. Indoor growers who use LEDs or lighting systems with an abundance of UV are most likely to experience this phenomenon.

Reason #4: Cannabis Plant Stress

Lastly, red or purple stems can be a sign of plant stress. Unfortunately, there are many different stress-related issues that can cause discolored stems. Pathogens and/or pests can be a cause for red or purple stems. Also, nutrient deficiencies, whether caused by nutrient lockout, issues with pH, or lack of essential elements, could be the culprit. The key is to look beyond the pigmentation to see if there are any other tell-tale signs that may help pinpoint the problem. Pathogens, pests, and nutrient deficiencies will all exhibit symptoms, beyond purple/red stem pigmentation, that can be used to properly identify the problem. Once identified, a grower can put the appropriate treatment/action plan into place. I hope this answers your question.

Keep on Growing,
Lee G. Lyzit