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Cannabis Purple Stems

What Do Cannabis Purple Stems Mean and How to Handle Them?

Marijuana plants typically display signs when something’s not right. A common one is cannabis with purple stems.

Possible causes of the discoloration include:

  • Genetics
  • Stress
  • Pathogens
  • Improper soil pH
  • Nutrient deficiency

There’s no cause for alarm if you find that your plants are healthy and continue to develop as expected.

As we discuss the causes and remedies, you’ll learn not to worry about cannabis with purple stems. You’ll also find out what to do to get your plant’s health back, if necessary.

Why are cannabis stems turning purple?

Red or violet marijuana plants? That’s not right, or is it?

If your plant looks healthy, then in most cases, the discoloration is no reason to worry.

So, what do purple stems mean?

Your plant could be telling you beforehand of potential issues, such as stunted growth and poor yield.

Before you react, observe your purple-stemmed plant for two weeks to see if there are symptoms that indicate other causes.

Cannabis purple stem
An example of a cannabis purple stem

Purple stems caused by genetics (you have nothing to worry about)

The violet hue is often due to genetics. Many cultivars, such as Granddaddy Purple and Purple Kush, have brilliant purple shades and stems turning purple too.

If your cannabis plant’s color is a result of genetics, it’ll look healthy and show no other signs of distress. It may just be adapting to the environment. 


Although most cultivars are resistant to diseases and cannabis pests, pathogens in the soil can prevent your marijuana plant from getting nutrients and water.

One of the signs you’ll notice is the purple stems on your cannabis plants. To pinpoint the exact cause, you must look for other signs besides the hue. 

Once you’ve confirmed the root of the problem, you must take immediate action before the deadly pathogen spreads and destroys your other plants. 

Nutrient deficiency

Besides water, your marijuana plants need a proper nutrient diet to thrive. If they don’t get enough nutrition, their growth will be stunted, and they’ll produce fewer and smaller buds. 

Purple stems on your cannabis plant are its way of telling you that they need help. The violet hue typically indicates a phosphorus, nitrogen, or potassium deficiency. Click here to browse all the cannabis deficiencies to determine which one you may have. Once you’ve identified the deficient nutrient, all you have to do is feed it to your plant, and it’ll recover. 

Incorrect pH

Nutrient deficiency is often related to soil pH. Weed plants prefer soil that’s slightly acidic. 

If your soil has a pH level that’s too high or too low, you’ll get weed with purple stems. Then, no matter how much you water your marijuana plant, it may not absorb the nutrients efficiently.

You have to make sure your soil is at the optimum pH level. At 6.5, you’ll see positive results in no time.

We suggest you use tools to test the conductivity and pH of your soil to know how well your plant is obtaining its nutrients from the marijuana fertilizer.

Temperature fluctuations

Purple stems on weed plants can result from temperature changes, especially if they’re purple strains. These cultivars develop violet hues when exposed to cold temperatures at night.

purple stems on weed: is it ok?
Purple stems can be caused by incorrect temperature

If your plant appears purple or red after a cold night, there may be no cause for worry. Just keep a close eye on it over the next few days to see if it grows normally.

If there is slowed growth and the purple cannabis stems show signs of stress, raise the temperature in your room if you’re cultivating indoors. 

If your plants are outside, move them inside, where you have more control over the temperature.

Be aware of the level of humidity for growing weed. Abrupt and extreme temperature fluctuations can also affect your plants. 

For instance, if the outdoor temperature drops from 80 degrees Fahrenheit in the daytime to 50 degrees at night, the drastic change can be the cause of your cannabis stems turning purple. 

When cultivating indoors, control the temperature so that at night it does not get more than 10–15 degrees cooler than in the daytime.

The ideal cannabis temperature should be within 68 to 77 degrees Fahrenheit. 


Cannabis stress can also cause a plant to have purple stems. However, as there are several stress-related causes, you must look closely at the other signs to identify the root cause of the discoloration.

Here are typical stressors to consider:

  • Root shock – this often occurs when transplanting cannabis. If you notice weeds with purple stems after being transplanted, give your plant lots of TLC to help it recover quickly.
  • Pests or diseases – some marijuana cultivars are more susceptible to pests and diseases than others. Besides cannabis with purple stems, you should expect to find signs such as damaged leaves, slowed growth, and signs of mildew and pests. 
  • Temperature or humidity issues – control the temperature, and you’ll reduce the stress that causes purple-stemmed plants. 
  • Light/heat stress – although marijuana cultivars generally love plenty of sunshine, too much heat can cause damage. 

Be sure to act fast to rectify any problems before they damage or kill your plant.

Why are my cannabis stems turning purple?

How to treat purple stems? Patience can be the solution

Typically, cannabis with purple stems can be linked to:

  • Genetics – anthocyanins break down as temperatures rise and change the strain’s hue to purple. There’s nothing to treat in this instance.
  • Plant tissue pH – more specifically, soil pH, which can’t be too low or too high. A slight acidic level of 6.5 is ideal.
  • Light spectrum and quantity – when your plant is exposed to too much light, you can see its stems turning purple. Make sure that your marijuana grow lights are not too close.
  • Pathogens – treat your soil to kill the pathogens.
  • Nutrient deficiency – lack of certain nutrients can also lead to your plant having purple stems. Identify the shortage and feed it what it needs.

Whatever the issue may be, be patient and observe your plant for about two weeks to see if it grows normally. Take this time to check for other signs to help you pinpoint the problem.

Frequently Asked Questions

Here are some commonly-asked questions and our quick guide.

How do you treat purple stems?

If your plant’s stems turning purple is due to genetics, leave it alone. If it’s a fungal or pH imbalance problem, treating the soil will resolve the issue. Growing indoors will help you manage temperature changes and control the lighting. Feeding your plant the nutrient it lacks will help it thrive again.

Why do phosphorus-deficient plants turn purple?

Your cannabis plant may have purple stems because of phosphorus deficiency. Phosphorus is vital for plants’ general health and fitness. Its functions include using the sun’s energy to make useful compounds. It’s also the main component of the plant’s energy unit (ATP).

How do I fix nutrient lockout? 

Cannabis with purple stems can be due to nutrient lockout, which is the cause of your plant’s inability to absorb nourishment from the soil. Fortunately, fixing the problem is straightforward. Stop feeding your plant more nutrients, as that’ll only aggravate the problem. 

Flush your plant with pH-balanced water to dilute the minerals and let the soil dry before you water again. Then, wait a few days before adding nutrients. 

Should you be concerned about purple stems?

Seeing cannabis with purple stems the first time may be scary, but now that you know the causes and how to deal with them effectively, you’ll realize it’s not that big a deal.

As you progress, you’ll learn that observing and understanding your plant’s responses to stimuli is as essential as the other cultivation tasks you perform to raise a healthy marijuana plant.

With knowledge and experience, you’ll enjoy fruitful harvests for a long time.

If you’re looking for seeds that produce purple stem plants we have you covered. For those of you concerned with your plant health, our cannabis seeds and nutrient packs can give your crop the boost they need.

AUTHORED BY: Douglas Kester Douglas Kester, a cannabis growing expert at I49 Seed Bank. He has been working in the weed industry for more than 10 years. During that period, he built up a vast experience and depth of expertise in this field. Douglas has a detailed understanding of every aspect of marijuana, from its cultivation and species to the effects it brings. He's also up to date on all the cannabis-related legislation nuances.

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