Why Are My Cannabis Stems Turning Purple

Why Are My Cannabis Stems Turning Purple

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So, you are just starting to grow your pot plants, but oh no, instead of green, you cannabis stems have a purple tinge to them. Sometimes your cannabis stems might have a purple hue and sometimes they can be outright purple, a really dark purple.

Now, sometimes this happens with seedlings and sometimes it happens with marijuana plants that are already well into the vegetative state of growth. This begs the question, why are my cannabis stems turning purple?

Well, this is usually due to two reasons, both of which are not big deals at all.

  1. Your cannabis stems may be turning purple because that’s just the way the strain looks.
  2. Stems turning purple may be a sign of a nutrient deficiency.

2 Reasons Why Your Marijuana Plant Stems Are Turning Purple

Alright, so our cannabis plant’s stems are turning purple, and this could be simply due to genetics, or it could be a nutrient deficiency. Let’s take a look at both right now.

1. Genetics

Ok, so some weed plants just have purple stems. Now, generally speaking, most cannabis plants have green stems. This is the normal color. However, many seedlings, especially in the first couple weeks of growth, will have purple stems, or at least a purple hue to them.

They will usually grow out of this in a couple of weeks, and the stems will turn their normal green color. Also, some weed plants may develop purple or purplish stems during the vegetative state of growth, generally towards the end of this stage, and during the flowering stage too.

This could be nothing more than genetics. There are a select few weed plants out there which have purple stems. If you don’t see any other issues with the marijuana plant, there is absolutely no cause for concern and no corrective action needs to be taken.

If you notice purple stems, just leave them, and if there are no other signs of trouble, such as curled or drooping leaves, slowed growth, or any other such things, you don’t need to do anything.

All you’ve got is a cool looking purple weed plant. However, if you see other signs of trouble, as you will see below, you will need to take corrective action immediately.

2. A Nutrient Deficiency – Magnesium

If your pot plant has purple or purplish stems, you may have a nutrient deficiency issue, specially a magnesium deficiency. As mentioned above, if your weed plants have a magnesium deficiency, you may see purple stems. However, that is not all you will see.

A classic sign of a magnesium deficiency in pot plants is when the leaves slowly turn yellow, especially the tips of the leaves, and eventually, they will turn a red-ish black color. If you see this occurring, you know that a magnesium deficiency is to blame.

Usually, a magnesium deficiency is pretty simply to solve, as it can be caused by a lack of magnesium in the soil or a lack of magnesium in your water or fertilizer.

How to Fix A Nutrient Deficiency

This issue is pretty easy to solve, as you can mix some water with magnesium sulfate to make a spray which you then spray over the leaves.

Spray the leaves every 3 days until the problem is corrected, using a pure water spray every 10 days to ensure that no residue builds up on the leaves. You can also mix some magnesium sulfate into the water you use to feed your weed plants.

The other issue which can cause a magnesium deficiency in your weed plants, and really all kinds of nutrient deficiencies, is if the pH level of the soil and water are not ideal. For the best nutrient and magnesium uptake, your soil and water should have a pH level between 6.0 and 6.5.

So, you need to measure the pH level regularly (get yourself a good pH meter), and if it’s off, take corrective action, generally done with pH altering chemicals which can be bought in any garden center or weed grow shop.


It’s as simple as that people. Either your weed plants have a naturally purple tinge to their stems, or the purple stems are being caused by a magnesium deficiency. One requires no solution at all, as purple genetics are not a problem, and the other, the magnesium deficiency, is generally quite easy to solve through some simple corrective measures.