Why Do My Marijuana Plants Have Purple Stems, Stalks, Petioles?

Most cannabis growers worry if we see purple stems, stalks, and petioles on our marijuana plants.

The color of leaves, stems, stalks, and petioles are a big part of our marijuana plant’s language as it tries to tell us if it’s happy or suffering.

Purple stems may be telling you that your plants will grow slower, buds will form slowly, buds will be smaller and less developed.

Purple stems, stalks, and petioles may be a warning sign of problems with nutrients, root zone pH, plant health, or grow room environment.

A stressed cannabis plant will often have purple stems and other parts.

But… some marijuana strains are genetically programmed to have purple stalks, stems, petioles, and leaves.

Check out these beautiful purple marijuana strains, for example.

You can discover if the strain you’re growing is genetically programmed to be purple by looking at strain descriptions, photos, and YouTube videos… and by asking the strain’s breeder.

If your grow op has multiple strains all fed and lit the same way but only one strain is going purple, and if the purple strain is growing as well as all the other strains, you’ve probably got nothing to worry about.

However if you’re growing multiple strains and most or all plants have purple stems, petioles, and stalks, you’ve likely got problems to diagnose and fix, especially if the strains aren’t known to be purple strains.

The most common purple problems come from hydroponics nutrients disorders and root zone issues.

Phosphorus and magnesium lockout or deficiencies are at the top of the list.

(Read here about nutrients lockout).

Purple stems can also come from nitrogen or potassium deficiencies or lockouts.

Nutrients issues can be frustratingly complicated.

Please look at this series of articles giving you a scientific way of diagnosing and fixing nutrients problems.

Fixing magnesium deficiencies is easier than fixing phosphorus, nitrogen, or potassium problems.

You root or foliar feed Epsom salts at a rate of ¼ teaspoon of Epsom salts per gallon root feed or a 130 ppm foliar feed at 5.7 pH.

You can root feed Sensi Cal-Mag in grow phase and the first three weeks of bloom phase.

In bloom phase, root feed Bud Candy, Bud Factor X, and Microbial Munch (all three have magnesium).

Fixing phosphorus deficiency is challenging because there are few solo phosphorus supplements.

If I suspect phosphorus deficiency, I add B-52 in grow phase, and B-52 and Big Bud in bloom phase.

The B-52 provides added phosphorus, nitrogen, and potassium, along with B vitamins that help stressed plants.

B-vitamins also increase bud development.

Beware that most bloom boosters contain way too much phosphorus in relation to potassium.

Inferior hydroponics base nutrients and supplements can create lockout and deficiencies, as can incorrect root zone pH, bad water, overwatering, and overfeeding.

And if you routinely add a solo element like magnesium into your root zone, you may eventually create other problems, such as nutrients lockout.

Only feed materials such as Epsom salts for one or two watering cycles, then stop using that material, and see what happens.

If you’ve tried flushing, adding individual nutrient elements such as magnesium, eliminating grow room environmental problems, pests, and diseases, and you still have purple stems, petioles and other plant parts, watch your purpling plants closely.

If they’re purple but they’re otherwise growing well, no worries.

But if they’re growing slowly or not at all, if bud development is delayed and inadequate, if they’re not using much water or nutrients, this is most likely a sign of a defective strain.

This is especially verified if you’re growing other strains in the exact same environment and they’re doing great.

For example, I had a 3000-watt grow room with five different strains.

Four strains grew fine and yielded big.

One strain had purple stems starting three weeks into grow phase.

I couldn’t fix it.

Those plants grew slowly with weak stems and stalks.

They didn’t yield enough weight, even though the buds were potent.

I won’t grow that strain again!