Sulphur deficiency in cannabis plants

How to Spot and Correct a Cannabis Sulphur Deficiency


Sulphur deficiency (or Sulfur deficiency) happens very rarely in cannabis plants so the likelihood of your plants suffering from it is highly unlikely. Having said that, they do happen from time to time so it’s important to know how to spot them and how to correct them quickly.

Sulphur deficiencies are aggressive and take a heavy toll on marijuana plants. In worst case scenarios, the plant dies or the yield gets decimated. In the best case, the terpene production is stunted and the end product ends up bland and weak.

Sulphur deficiency in cannabis plants

(S) Sulphur (Sulfur): Needed in protein synthesis, water uptake, fruiting and seeding, a natural fungicide. Improves terpene and cannabinoid production and assists in photosynthesis.

Deficiency: Sulphur deficiency is uncommon but can cause young leaves to turn yellow with purple bases.

Toxicity: Excessive Sulphur slows growth and leaves grow out smaller than normal.

Micronutrient: Absorbed in small to minute quantities. They are generally less well known than the macronutrients since most plant foods don’t contain them.

The Role of Sulphur in Cannabis Plants

Sulphur may be a micronutrient but it plays an important role in a couple of vital plant functions. The mission of Sulphur is in the production of vitamins, proteins, amino acids, and enzymes that keeps the plant healthy and thriving.

For us as cannabis growers, it’s important to know that it also is a key component in the production of oils and terpenes, which greatly influence the aroma, flavor, and potency of the plant. When the amount of Sulphur is low in the flowering stage, you can easily end up with weak, tasteless, and lackluster buds.

The Symptoms of Sulphur Deficiency

A lack of adequate Sulphur levels can result in yellowing of the leaves, stunted growth, and even woody stems that make the plant feel rigid and hard.

One of the primary causes of Sulphur deficiency is a lack of sulphur in the growing medium or nutrient solution (shocker). It’s common for soil growers who use sandy soil because Sulphur has a tendency to bind to clay and organic matter, making it less readily available for root uptake.

For hydroponic growers who use RO water, the nutrient solution needs to contain the right amounts of sulphur from the get-go. Potassium Sulfate is the most common source of Sulphur used in hydroponic systems and it is fairly easy to regulate as long as you follow the instructions on the label.

The Early Stage of Sulphur Deficiency

In the early stages of deficiency of Sulphur, the newer leaves will start turning yellow while the older, lower leaves remain green. Now, don’t confuse this with a nitrogen deficiency where the yellowing begins at the bottom.

Yellow top leaves are also common with light-burn so check the distance to the light source before jumping to conclusions. Remember that Sulphur deficiencies are quite uncommon and cannabis plants only need a minimal amount to remain happy and healthy.

The Progression of Sulphur Deficiency

As the Sulphur deficiency progresses, the yellowing spreads to older leaves and throughout the entire plant as they fade from dark green to light green and later to yellow. You will also notice that the plant’s growth slows down, and you sense a distinct lack of aroma.

If you catch these symptoms, you need to take action right away (see below).

The Late Stage of Sulphur Deficiency

In the final stages, the deficiency can make the underside of the leaves turn a sickly reddish-purple or even brown color and the plant starts developing woody stems and decreased yield.

At this point, you may have to surrender and let go of the plant. 

Sulphur deficiency cannabis

Causes and Misdiagnoses of Sulphur Deficiency

A variety of factors can cause Sulphur deficiency, including incorrect pH levels that lead to nutrient lockout, insufficient nutrients in the soil, and overwatering. It’s quite common for Sulphur deficiency to be misdiagnosed as nitrogen deficiency or light-burn because the early symptoms are quite similar.

So How Do You Fix a Sulphur Deficiency in Cannabis Plants?

Alright, now let’s get down to business! You spotted the telltale signs of Sulphur deficiency from the symptoms above. 

Once you’ve confirmed the culprit, you need to start by checking and adjusting the pH level of your soil or growing medium. Use a pH meter to check that the pH is between 6.0 – 6.5 for soil or 5.5 – 6.0 for hydroponics. If the pH is way off, you may need to flush the system and add in a new and balanced nutrient solution with pH-balanced water. If the pH is slightly off, you need to bring the acidity up or down accordingly.


Learn how to spot and fix cannabis nutrient deficiencies

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