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Cannabis seeds with purple stems

All You Need To Know About Red Stems On Cannabis Plants

Even if everything in your garden is on point, you may see a couple of stems turning red or purple. Red stems often come with other symptoms such as yellowing, or burnt and clawing leaves, and these are found to be caused by 6 common things. Red or purple stems are often caused by lighting, genetics, temperature, stress, nutrient deficiencies, and pH levels, so read along and learn how to prevent it.

1. Red Stems On Cannabis Plants

When you encounter red or purplish stems for the first time, it may be concerning but there are several things that can cause them and many of the reasons are not bad. While the main thing that causes red stems is genetics, things like temperature fluctuations, stress, and light intensity can also cause them.

This means that f your plant appears healthy, you don’t have to worry about it, it’s most likely caused by genetics but if the red stems come with yellowing, brown spots, or curly leaves, then you should definitely find out what’s causing it and fix it as soon as possible. So for those of you who are dealing with this issue, here are the main causes and how you can fix them to avoid more serious problems.

2. Light Intensity

If the stems are exposed to strong direct lighting, they may turn purple, red, or pink. When this happens, the stems exposed to light will turn red but the lower stems remain green. This is a defense mechanism cannabis plants have against strong light, especially light fixtures that emit UV rays.

Red stems are often more common when performing plant training techniques due to evening out the canopy, which exposes all stems to direct light. So if the majority of stems are green but you find a couple of red stems, there’s nothing to worry about as long as your plants are strong and healthy.


Now, if your plants are showing red stems but they’re not 100% healthy, make sure you dim down your light fixture or adjust the height and keep an eye out on how they develop. If the problem persists, continue adjusting your light’s height until your plants are doing well.

3. Genetics

Some strains, especially those that tend to exhibit purple leaves or buds, can naturally grow pink, red, or purple stems. When red stems are caused by genetics, they usually develop a lighter pinkish or reddish color on all stems, not only on the ones that are getting direct light.

If this is the case, there’s no need to worry because it’s a genetic trait and won’t affect plant growth other than the different stem colors.

4. Temperature

A 5 – 10 °C difference in temperature between day and nighttime temperatures can promote red, pink, or purple stems and sometimes leaves. So if the different stem colors appear after a cold night, it’s most likely caused by temperature fluctuations.

5. Plant Stress

In some cases, stress such as overwatering, heat, or a bug infestation may cause discolored stems, that’s why it’s important to keep your grow space clean, maintain good growing conditions and check your plants at least once a day. Due to being caused by different types of stress, it may be hard to identify what’s causing the red stems. For example, outdoor growers may think the red stems are being caused by a nutrient deficiency but, in reality, it’s being caused by a planthopper infestation, for example. The thing is, stress can be caused by anything and each strain is different so it’s important you get to know the specific strain you’re growing and learn the do’s and don’ts if you’re dealing with red stems often and don’t know what’s causing them.

6. Nutrient Deficiencies

If the red stems come with yellowing, it’s a sign your plant is lacking the following nutrients:

  • Phosphorus and;
  • Magnesium.

Discoloration of the stems due to a lack of nutrients is more common when you haven’t fed your cannabis plant for a long time or when the products you’re using don’t contain them. For example, if you grow in an inert substrate such as coco fiber or rockwool, it’s essential you feed your plants before the 2-3 weeks of plant growth.

Although it’s still not 100% confirmed, growers have noticed that a lack of phosphorus or magnesium usually causes discoloration of the stems, which often come with other symptoms such as yellowing of the leaves.


This can be avoided by using slow-release nutrients or by growing in super soil, which contains all the nutrients your plants need from seed to harvest. So if you’re dealing with this, make sure you feed your plant as soon as possible or look for fertilizers that contain both phosphorus and magnesium, this way you prevent this from happening.

7. PH levels

If you’ve eliminated all the cases mentioned above, the stem discoloration your plants have may be due to a nutrient deficiency caused by pH levels. PH levels can affect nutrient absorption, meaning that even if you feed your plants the nutrients it needs, it won’t be able to absorb them, causing a nutrient deficiency.

When the red stems are caused by pH levels, you’ll often find other symptoms such as leaves with burnt edges, curling leaves, burnt tips, and yellowing among other more serious symptoms. Now, you don’t need to have a pH pen to grow cannabis but it’s highly recommended to get one in case you’re dealing with this kind of problem because the only way to fix this kind of problem is to test the nutrient’s solution pH and water with the pH’d nutrient solution until the ph of the substrate is within the correct range.


In case you’ve identified the red stems are caused by pH problems, here’s what you should do. First of all, mix your nutrient solution as usual. Use ph drops or a digital ph pen to check the nutrient solution’s pH, it should range between:

  • 6.0 – 7.0 when growing in soil and;
  • 5.5 – 6.5 when growing in coco fiber and hydro.

If the ph is too high or too low, use any pH Up or pH Down to adjust it and check again until it’s within the desired range. Water your plants with the pH’d nutrient solution, if you’re still having problems, the problem is in the substrate so flush for a couple of days and then continue feeding normally with the pH’d nutrient solution.

In case you’re having a hard time identifying what’s causing red stems on your cannabis plants, here’s a table to help you out.

Red Stem On Cannabis Plants: Causes and Symptoms
Cause Most Common Stem color Symptoms
Light intensity Reddish or dark pink No additional symptoms
Genetics Dark purple, dark red, or dark pink Purple leaves and buds in some cases
Temperature Light red or light pink Bigger fan leaves may exhibit same color as stem
Plant stress Light pink or red Yellowing, brown spots or bugs
Nutrient deficiencies Light red or pink Yellowing and/or burnt tips
PH levels Light red, pink, or light purple Yellowing, burnt tips and brown spots

Have in mind that all plants are different, some plants may never show different colors and others may show them in places that you couldn’t even imagine, such as the pistils or trichomes. So remember, this is just a guideline to help you identify what’s causing problems in your garden!

8. In Conclusion

These are the main things growers have found to cause red stems but they’re in no way confirmed scientifically, so if you’re dealing with red stems, even if there aren’t any bad symptoms, make sure to write down what changes you’ve made and help the grower community find out what causes them.

If you’ve encountered red, pink, or purple stems before, feel free to help fellow growers by leaving a comment in the comment section below!

Stems of cannabis plants turning purple, how do I fix this?

Question: Help! My cannabis plants are young (growing in soil indoors with sunlight and my leaves are medium sized) yet my main stems are turning purple from the top downwards. Have you seen this before?

Answer: When a cannabis plant or seedling has a purple stem without any other signs of problems, it is often the result of genetics. However, sometimes you’ll see red stems (pictured below) which are often caused by light exposure (kind of like a “tan”), nutrient deficiencies, various types of stress, poor environment, or pH problems.

Wait a week or two before making any alterations if your plant otherwise appears healthy and is growing fast.

If there are no other symptoms and the rest of the plant is growing fast and healthy, red stems usually aren’t a big deal. As long as you’re continuing to take good care of your plant and responding quickly to any other problems, you should be okay.

These red stems were caused by transplant shock and overall stress, but the clone just needed some TLC and time to grow out of it.

Truly purple stems are often caused by genetics

If you believe there is a nutrient problem with your cannabis plant, for example, if your plant is also growing slowly or the leaves are discolored, then the plant may be suffering from…

Cannabis purple stems, how can I fix it?

If you’ve ever asked yourself this question: “Why does my weed plant have purple stems?“, you have come to the right post. Is it worrying? Am I in time to fix it? What exactly does it mean? From now on you will know what Cannabis purple stems means.

Stems turning purple. Only for one reason?

Absolutely not, stems turning purple for different reasons. Stress can be a cause (nutritional deficiency, pests, ph or light problems. ), but there are also cases where you don’t have to worry. Let’s go step by step, we are sure you will identify your case.

Let’s start with the least worrying, your plants are probably perfectly fine and you don’t need to know anything else.

Strains with purple stems: Auto Dark Purple

If you are worrying about a strain that is already purple and also characterized by a very dark foliage: Relax. You have in front of you a strain with purple stem. As you know, the world of marijuana is incredible, among many other things, because of the unique pigmentation of each strain.

The best possible example is the Auto Dark Purple of Delicious Seeds:

Yes, purple cannabis stems may be due to genetic.

Anyway, beyond the color, you know better than anyone if something is going wrong. It is possible that this is your case, but you still don’t know what you have to change concretely so that your plant not only looks better but also works better. So, now let’s get down to business.

What causes purple stems on cannabis plants

As we have already mentioned, stress is the word that encompasses most of the things what causes purple stems on cannabis plants. But let’s get down to the specifics of your problem:

Fungus: Does the word Fusarium ring a bell? It is the pathology that can be giving a purple color to the stem of your weed. If your plant is large, you have many chances that you have been visited by this fungus, since it affects these specimens in a special way.

Ph: We have put it in second place, but the first thing you have to do if you have not yet found an explanation for this problem is to measure the pH. If it is too high or too low, it may very well be the cause of that reddish or purple tone.

– Too cold: In this case, what may be causing your cannabis purple stems are too low temperatures. If you just turned on the bulb, try changing this which will probably change the color as well.

– Insufficient nutrients: Many times we get complicated, and what causes purple stem weeds is a nutrient deficiency in our plant. Yes, as simple as that.

There is one last factor that we haven’t talked about that also causes weed with purple stem. As you can imagine, we have not discussed it because it is not as important as the rest, and that is lighting.

It is likely that if you use lighting methods with a lot of exposure to your crop, the color of the stem will turn red or purple. Don’t worry, it’s okay. If your plants look good, everything is going according to plan.

As a final conclusion, we are left with this last sentence. If your grass looks good, don’t be alarmed. After all, if your plant has a problem, it will only be one more symptom of the problem.