What Is Sulfur Deficiency In Cannabis Plants?

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Added 28 April 2022

Your plant is growing slower than expected, and the leaves turn yellow. You suspect it's nitrogen deficiency and take necessary measures to correct it. But is the plant really suffering from a deficiency of nitrogen, or is it something else?

Most probably, your plant is suffering from a sulfur deficiency. 

Sulfur is an essential nutrient that cannabis requires in small amounts, but the plant can suffer from various issues when deficient. Identifying a sulfur deficiency can be challenging for a beginner since it's similar to other deficiencies. 

However, this article should help you identify and rectify the problem. Learn all about sulfur deficiency and help your plant yield abundant buds.

What is the Sulfur Cycle in Cannabis?


Along with calcium and magnesium, sulfur is another secondary nutrient that the cannabis plant requires to grow well. This element is necessary for various essential functions like photosynthesis, production of amino acids and proteins, and secondary metabolism.

Sulfur in its elemental form is present in nature, but it is not soluble in water. So, your plant cannot absorb it properly. Instead, your plant absorbs sulfur in the form of sulfate (SO4), which is naturally present in the soil.

The microorganisms in the soil metabolize sulfur and turn it into sulfate, which is how soil becomes sulfur-rich for the plant and stays replenished in the soil.

Here are some of the top functions of sulfur in the cannabis plant:

  • Sulfur contributes to the formation of enzymes in the plant.
  • Since sulfur is present in amino acids, it also helps with the production of proteins.
  • Sulfur is also responsible for developing chlorophyll, which gives your plant the green color and makes photosynthesis possible.
  • As a secondary role, sulfur aids in the nitrogen metabolism, among other processes, in the plant. This is why your plant may simultaneously suffer from both nitrogen and sulfur deficiencies sometimes. 

However, due to incorrect soil or grow conditions, your plant may not have access to adequate sulfur or sulfate, which can cause sulfur deficiency.

How to Identify Sulfur Deficiency?

Stages of Sulfur deficiency

Sulfur deficiency is not as common as other deficiencies, but you may still come across it in your garden. However, you must not confuse it with nitrogen deficiency since both the deficiencies exhibit similar symptomologies.

The key is to figure out where the symptoms appeared first.

Nitrogen is a mobile nutrient, where the plant will transfer nitrogen from older leaves to new ones during a deficiency. This leads to the symptoms of nitrogen deficiency becoming apparent on the lower leaves first. 

On the other hand, sulfur is semi-mobile. Therefore, the symptoms of sulfur deficiency first become apparent on the middle tier of the plant, where the leaves have recently matured.

During the initial days of the problem, you will start seeing a pale discoloration of the leaves in the middle tiers, with the leaves turning yellow (or orange, pink, or red). This is due to a decrease in chlorophyll production.

This discoloration begins on the underside and base of the leaf and gradually moves outwards towards the edges, with the discoloration intensifying each day.

Over time, the leaves may also exhibit necrotic spots due to sun burning, the plant may display slow growth, or the flowers may start dying.

What Causes Sulfur Deficiency?

Sulfur deficiency

Sulfur is naturally present in the soil, but many other factors dictate its uptake for the plant. Here are some of the common reasons behind sulfur deficiency.

Sulfur is Not Naturally Available

In the past, sulfur was present in the ecosystem thanks to us burning a lot of high-sulfur coal. But in the recent decades, the sulfur in the atmosphere started declining as people began using natural gas or low-sulfur coal.

Perhaps this may be why your plant may be experiencing sulfur deficiency, especially if you live in a region where a lot of coal isn't burnt or sulfur doesn't occur naturally in the ecosystem.

Another reason why your plant may be experiencing sulfur deficiency is if your region's water supply does not contain enough sulfur.

pH Problems

Like most other deficiencies, sulfur deficiency can also be attributed to incorrect pH levels at the root zone. If the growing medium is too alkaline or acidic, it can hamper the roots' ability to absorb nutrients like sulfur properly.

Incorrect Fertilizers

Since cannabis does not require sulfur in high amounts, fertilizer manufacturers sometimes overlook it — it is usually only listed as an ingredient. So, you might be using a fertilizer with low or no sulfur amount, which may be causing this problem. In addition, soil growers will have no issues since natural soil usually contains sulfur; however, the plant will face issues if you use incorrect fertilizers in soilless mediums. 

Low Quality Grow Medium

As mentioned above, natural mediums like soil contain sulfur; however, if you use low-quality or cheap soil, it may be devoid of sulfur (among other essential nutrients), which can also cause a sulfur deficiency in your plant.

How to Fix Sulfur Deficiency?

Fortunately, sulfur deficiency is relatively easy to fix — a few hours and little money can help you remedy this problem within a few days. So let's take a look at the best solutions to sulfur deficiency.

Check and Rebalance the pH

Rebalance pH

First, you need to check and rebalance the pH in the soil medium. Ideally, the plant will be able to absorb sulfur when the pH is above 5.5 in both soil and hydro mediums. 

Try to maintain the pH at 6.0 to ensure the plant can intake optimal amounts of sulfur. On the other hand, make sure the pH doesn't dip below 5.5 as it can lead to various deficiencies along with sulfur. 

To check the pH of the root zone, use a pH meter to measure the nutrient solution and runoff water. If the readings are off, you need to rebalance the pH.

You need to flush the growing medium with clean water (preferably RO) to wash off any residual nutrients and feed the plant nutrient solution with the correct pH levels. There are many pH balancing kits available in horticultural stores that you can purchase, too.

Use Epsom Salt

Use epsom salt

If the pH is ideal for the plant, you need to give your plant a sulfur boost, which you can do with Epsom salt. Epsom salt is nothing but magnesium sulfate, made up of sulfur, oxygen, and magnesium. And it is water-soluble, which releases sulfate ions (and magnesium) in the growing medium.

The best part about Epsom salt is that it is super cheap to buy, and you can get them even at beauty stores — it has a lot of health benefits for you as well.

Just add 1 to 2 teaspoons of Epsom salt to 1 gallon of water and feed it to your plant as usual. This will give your plant the much-needed boost and halt the progression. Do this, especially if your water supply does not have sulfur.

However, avoid mixing Epsom salt with calcium-based fertilizers as it can form an insoluble precipitate that can cause a nutrient lockout.

Buy Sulfur-Specific Fertilizers

Use sulfur fertilizers

If you are looking for a more plant-oriented solution, you can also buy sulfur-rich fertilizers from your local gardening supply store. Some of the most popular fertilizers to cure sulfur deficiency are:

  • Calcium sulfate (15% to 18% sulfur)
  • Potassium sulfate (around 18% sulfur)
  • Potassium magnesium sulfate (around 22% sulfur)
  • Ammonium sulfate (24% sulfur)

Since each manufacturer uses a unique recipe, the application process differs a lot. So, read the manufacturer's instructions carefully before applying the fertilizer to your plant.

Use a Manure Compost

Use manure compost

A more organic approach to adding more sulfur to your grow medium is using manure compost since it is rich in sulfur. Your best bet here is using mushroom compost. 

Simply apply a layer of compost over your garden bed. It will slowly leach sulfur into the grow medium, ensuring a constant supply of nutrients for your plant.

How Much Sulfur Does the Plant Require?

The sulfur amount in the root zone and fertilizer must be between 50 to 200 ppm for the best uptake and plant growth. Even if the sulfur content is slightly higher, it does not affect the plant much. However, going over 200 ppm can inhibit the roots from absorbing molybdenum or boron and cause sulfur toxicity.

Above 300 ppm, sulfur toxicity occurs, which can exhibit in the form of brown spots on the leaf tips — similar symptomology as excessive salt in the root zone.

You must focus on balancing it all so that your plant has enough sulfur to absorb but not too much. For this, you can use the remedies mentioned above.

And if you want to know how much sulfur your fertilizer contains, you can even send it to a dedicated laboratory to know for sure.

Summary: What is Sulfur Deficiency in Cannabis Plants?

Sulfur is an essential ingredient that goes into making a healthy plant (and delicious buds), but you need to ensure your plant gets enough of it. For example, if your plant is experiencing yellowing of leaves and stunted growth, it might be suffering from a sulfur deficiency.

Verify it is sulfur deficiency and not nitrogen deficiency, and figure out what's causing it. For example, it might be a bad growing medium, water supply with not enough sulfur, pH imbalance, or something else. And use the methods listed above to remedy the problem.

Sulfur moves slowly through your plant, so it may take a few days before you start seeing improvement. And in some cases, the remedy may not reverse leaf chlorosis, but it will stop the deficiency from spreading further. 

In any case, do not panic — sulfur deficiency is quite an easy problem to fix.


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I look for sulfur in hell!🖐️👨‍🌾