The Importance Of Sulfur In Your Garden

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.

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 by miners over a lifetime could result in eye or lung disturbances. When handling sulfur, 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 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 sulfur is used 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 on a bright, sunny day in warm weather with no wind. The granular option, called wettable, must be diluted. Add water and apply per the instructions on the label.

Sulfur-based pesticides and fungicides can be purchased from garden stores.

Lower soil pH

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

This is effective, but slow; it can take several months to a year. It does occur faster in the summer when bacteria are active. Sprinkle directly onto the soil, then incorporate into the top three inches. The amount of sulfur needed will depend on the size of the area you’re amending along with the texture of your soil. These determine how quickly the reactions occur.

Periodic soil tests ensure 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 are stunted;
  • 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. Mineral fertilizers containing sulfur can be purchased at most garden supply stores.

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

Maria Webster
Maria is an award-winning landscaper turned expert horticultural writer, from the desert southwest. In addition to contributing to multiple home and garden outlets, she enjoys writing about mental health and personal growth & development. Writing is a favorite hobby, and she regularly publishes personal essays and elegiac poetry on Medium, where she's been curated in multiple niches. Her other passions include horses and cooking. Maria attended college in Texas and earned a bachelor's degree in education. She's currently based in Arizona with her 80-pound Red Heeler/German Shepherd, Dodger.