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Solving Sulfur Problems in Cannabis Plants

by | Aug 29, 2022 | Cannabis, Getting Started, Nutrients, Troubleshooting

Sulfur is an essential plant nutrient for cannabis. It is a sulfur deficiency that leads to stunted growth and yellowing leaves, among other symptoms. If sulfur toxicity occurs, the leaves will become dark green to brown, and your plant will exhibit slower growth. In this article, we’ll go over what sulfur is, why it’s important to your cannabis plants, how a sulfur deficiency can hurt the plants, what happens when marijuana plants get too much of it, and how you can prevent sulfur toxicity from happening in the first place.

What is sulfur?

Sulfur is a mineral that is found in the earth’s crust. It is an essential nutrient for plants and is necessary for photosynthesis and other metabolic processes. When most people think of sulfur they envision the bright yellow mineral or powder. Unfortunately, cannabis plants can’t use sulfur in that form so it needs to be broken down by microbes to form sulfate, which is water-soluble and can be absorbed by the roots. For this reason, most nutrients used for cannabis plants will have sulfates to transfer the nutrients to the plant.

What is the sulfur cycle?

The sulfur cycle is the process that breaks down sulfur minerals into sulfate and moves them through the environment. The sulfur cycle starts with weathering, which is the breakdown of rocks and minerals by physical and chemical processes. This exposes sulfur-containing minerals to air and water, which start to oxidize them and release sulfuric acid. The sulfuric acid is then absorbed into the soil, which creates sulfuric acid salts. These sulfur-containing acids are what plants use to take up nutrients in their cells and create energy for themselves.

Sulfur is an essential nutrient that needs to be made available to cannabis plants but it can’t just come from sulfur powder or rocks since they can’t absorb it. The sulfur cycle is what makes sulfur available for absorption by cannabis plants and can be found in all types of fertilizers that contain sulfur or sulfates, such as calcium sulfate or potassium sulfate.

Why is sulfur important to cannabis?

Sulfur plays many roles in the health and growth of your marijuana plant but one role that is very important is that sulfur helps form proteins. These proteins are essential for the plant to make new cells, enzymes, hormones, and chlorophyll. Chlorophyll is what gives plants their green color and it is necessary for photosynthesis, the process that turns light into energy for the plant. Without sulfur, your cannabis plant will start to show symptoms of deficiency, such as yellowing leaves, stunted growth, and slow development.

Is sulfur a mobile or immobile nutrient?

Sulfur is a partially mobile nutrient meaning that it can move within the plant but not as easily as other nutrients like nitrogen or potassium. When sulfur is deficient in the plant, it will start to redistribute itself to where it is needed most, so you may see symptoms in different parts of the plant depending on how severe the deficiency is.

Is sulfur a macro or micronutrient?

Sulfur is a macronutrient which means that it is essential for plant growth and development. It is needed in larger quantities than micronutrients like zinc or iron.

What are the symptoms of sulfur deficiency in cannabis plants?

If your cannabis plant isn’t getting enough sulfur, you will start to see initial symptoms such as yellowing leaves, slow growth, and stunted development. The yellowing will typically start with the young leaves and work its way down the plant to the more mature leaves. The young, upper leaves may also appear lime green. Other adverse effects include the yellowing of the leaves in between the veins, or interveinal chlorosis, is also common as well as brown, burnt tips that curve down. The stem may also become woody and overall growth is stunted due to this nutrient deficiency.

How can I fix a sulfur deficiency in my cannabis plants?

The best way to fix sulfur deficiency is by adding sulfur but preferably a sulfate as those can immediately be absorbed by the plant’s root system. A sulfur deficiency can also be fixed by adding organic matter to the soil as it will help break down the minerals and add sulfuric acid to the environment but will also take a long time for the plant to absorb it. Be sure to test your soil pH levels and adjust accordingly as sulfur deficiencies are more common in acidic soils.

Is there any way to prevent sulfur deficiency in my cannabis plants?

One way to prevent sulfur deficiency is by using a fertilizer that contains sulfur, such as calcium sulfate. Other ways include adding compost or dehydrated manure to your soil which will add organic matter and sulfuric acid over time.

What are the symptoms of sulfur toxicity in cannabis plants?

Sulfur toxicity can be caused by too much sulfur in the soil and will exhibit a couple of noticeable visual symptoms. This typically only occurs when it is overused in the soil and becomes a salt, which isn’t absorbed by the plant roots but builds up around them instead. If your plant is suffering from too much sulfur, toxicity symptoms will include the leaves turning a dark green or even a brownish-green. After some time, your leaf margins and tips, or the area between the veins, will show brown spots and burn. The plant will also suffer from stunted growth.

How do I fix sulfur toxicity in my cannabis plants?

The way to fix sulfur toxicity is by flushing the soil with lots of water. This will help leach out any harmful salts that have built up in your plant’s root zone. To do this, simply pour two to three times as much PH’d water through your medium to rid yourself of any nutrient lockout or toxicity. This will also work for coco coir too but you will have to change your reservoirs and ensure you have the correct PH levels if you are using hydro as your medium as an incorrect PH issue could be the cause.

Is there any way to prevent sulfur toxicity in my cannabis plants?

One great way to prevent sulfur toxicity from occurring is by using a fertilizer formulated for cannabis. These cannabis-specific fertilizers are formulated with sulfur and calcium, which help to promote overall plant health by balancing out the nutrients for your plants whereas other generic nutrients may have an unbalanced fertilizer formula. Mixing Epsom salt, gypsum, and animal manure are organic ways to ensure your plant has enough sulfur in the soil and are less likely to cause toxicity than using nutrients. Lastly, always use the nutrients in the prescribed amounts or less. It is actually preferable to start at a half dose of the recommended dosage and work your way up if your plant needs it.


Sulfur is a mineral that occurs naturally in nature and is essential to plant health and without it the plant will shows symptoms of nutrient deficiency. Plants absorb sulfur after it has been broken down into a water-soluble sulfate, whether it has been done through the sulfur cycle, by microbes, or through a nutrient solution. It is a necessary macronutrient that is needed for many important processes in the plant but in particular photosynthesis.

If your plant is suffering from a sulfur deficiency, it will likely show lime green or yellowing new leaves with interveinal chlorosis working its way down the plant. Curved brown leaf tips will also occur. To fix a sulfur deficiency, add a nutrient that contains a sulfate and it can easily be prevented by using cannabis-specific soil from the start. Sulfur toxicity occurs when the plant has too much sulfur and the symptoms include dark green or brownish-green leaves and the browning of your leaf tips and margins too. To fix this in soil or coco, you will need to flush your plants. If you are growing using hydroponics, your reservoir will have to be changed and PH’d properly.

To prevent sulfur toxicity, use nutrients that are made for cannabis and in the prescribed amount or less as you can always add more if your plants need it.

Thank you for reading our article on sulfur deficiencies and toxicities, for more information please read our articles regarding flushing, PH’ing your water, coco coir, and soil.

To learn more about growing cannabis at home consider checking out our guides on: Getting Started, Troubleshooting, and Optimizing your Grow or search our Knowledge Base.

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