The Importance Of Sulfur In Your Garden

Updated: May 26, 2024

In your garden soil, sulfur is as important to your plants' vitality as phosphorus. Here's what you need to know to put sulfur to work in your garden.

Plants need exactly 22 things to exist: water, light and 20 essential elements that support their biochemical needs. As a gardener, you’re likely familiar with at least three of those elements — nitrogen, phosphorus and potassium.

What you may not know is that sulfur is another of those elements, and it’s just as crucial to plant health as phosphorus. Found in water, air, rock, animals, plants and our bodies, sulfur is absolutely essential for all living things.

Sources of Sulfur

Sulfur is abundant in the atmosphere, in the form of sulfur dioxide from man-made and natural processes. It’s also found in organic matter (compost, manure and decomposing plant matter), organic fertilizers (cow and pig manure) and mineral fertilizer.

Most of what we use in the garden starts as elemental sulfur. This occurs naturally in soil and deposits from hot springs, usually appearing as yellow crystals. But plant roots can only absorb sulfur in sulfate form, so it needs to be converted.

That’s where sulfur flour and flowers of sulfur come in. Both are created from elemental sulfur and are turned into sulfuric acid by soil bacteria, creating the sulfates needed by plants. Find out how often you can apply sulfur to your lawn.

Is Sulfur Safe To Use?

As a naturally occurring element, sulfur is safe to use. The Environmental Protection Agency has approved it for use in pesticides, fungicides, fertilizers and soil amendments, many of them certified organic. More than 200 products containing sulfur are on the market.

Though its toxicity is low, sulfur dust may irritate sensitive skin and eyes. Chronic, excessive sulfur dust exposure over a lifetime could result in eye or lung disturbances. Therefore, when handling sulfur, it is best to wear protective gear such as a respirator or mask, safety glasses and gloves.

What Are the Benefits of Sulfur in Gardening?

Over-fertilization, excessive rainfall leaching or long-term crop removal can deplete sulfur from soil. Adding some can help when the pH levels of the soil are too high (alkaline) or too low (acidic). Here are the ways sulfur benefits soil:

  1. Increased soil biodiversity. Biodiversity is important for the overall health of soil, because it helps create a balanced and healthy soil ecosystem. Different types of bacteria, fungi, and other microorganisms can help to break down organic matter and make nutrients available to plants.
  2. Improved soil structure. Sulfur helps form aggregates, clumps of soil particles held together by natural substances such as mucilage, waxes, or gums. They’re important for soil health because they provide stability and allow water and air to penetrate more easily.
  3. Enhanced nutrient availability. Sulfur helps soil particles to bind together, making it easier for plants to draw nutrients.
  4. Improved plant growth. Sulfur provides plants with essential nutrients. It’s important for the development of chlorophyll, to better absorb light energy from the sun. This results in improved photosynthesis and growth rates.
  5. Increased resistance to pests and diseases. Sulfur helps create a stronger immune system, making the plant harder for pests and diseases to attack.

How To Use Sulfur in Gardening

Here are the four main ways to use sulfur in the garden:

Pesticide/Fungicide

Sulfur is most effective as a pesticide. It’s also a strong fungicide and disinfectant. Preventative and curative, sulfur easily controls mildew, powdery mildew, red spider mites, ants, snakes, rodents and various other pests and diseases.

The powdered form in this application comes from sulfur flower, which can be sprinkled directly on plants. For best results, use it on a bright, sunny day in warm weather with no wind. The granular option, called wettable, must be diluted first. Add water and apply per the instructions on the label.

You can purchase sulfur-based pesticides and fungicides from garden stores.

Lower soil pH

Once you’ve added sulfur to the soil, bacteria go to work converting it to sulfuric acid. This is the biological process that lowers the soil’s pH. Sulfur flour (as opposed to the aforementioned sulfur flower) lowers soil pH more efficiently because it keeps the level down longer than any other treatment.

This is effective, but slow. It can take several months to a year. However, it occurs faster in the summer when bacteria are active. Sprinkle sulfur flour directly onto the soil, then incorporate it into the top three inches.

The amount of sulfur needed will depend on the size of the area you are amending along with the texture of your soil. These factors determine how quickly the reactions occur.

Doing periodic soil tests will help you to ensure that the pH isn’t lowered too much.

Treat sulfur deficiency

A sulfur deficiency can cause yellowing of the leaves, stunted growth, and poor fruit production. Other indicators could be an abnormal leaf color, especially a reddish purple hue.

Sulfur deficiency in plants can be tricky to diagnose because it looks so much like a nitrogen deficiency, with chlorosis (reduced chlorophyll content and coloration in leaves) the main symptom of both. Other signs of sulfur deficiency include:

  • Stunted young leaves;
  • Spindly stems;
  • Upper leaves are pale green or yellowing while lower leaves look OK.

Sulfur flour applied at a rate of one pound per 100 square feet, mixed into the top three inches of soil, results in appropriately fertile soil. This treatment increases sulfur content only and does not raise or lower any other nutrients.

Soil amendment or fertilizer

Sulfur is most effectively used as a soil amendment in preparation of soil before planting. Store-bought amendments are created by heating up a mix of flower of sulfur with another material called gypsum, until the flower of sulfur melts. Then it combines with the gypsum to create a solid resembling small bricks. These are crushed to create a soil amendment.

Sulfur fertilizes many types of plants because of its relationship with nutrients like nitrogen, phosphorus and potassium. You can purchase mineral fertilizers containing sulfur at most garden supply stores.

If you prefer to use the element in a purer form, sulfur flour should be mixed into the soil, while flowers of sulfur can be applied directly to the plants.