When soil is deficient in sulfur, plants can be short and spindly, with yellowish veins on their leaves and poor, or nonexistent, flower and fruit production. In the soil sulfur interacts with plant roots in two ways. First, sulfur, when converted by bacteria to sulfuric acid, lowers soil pH, increasing plant-root access to many nutrients. Second, sulfur plays a critical role in the formation of plant tissue proteins and vitamin formation.
To Lower Soil pH
Test several samples of soil from your intended planting area for the rating of acidity or alkalinity, commonly called pH. The pH level of your soil will determine how much elemental sulfur you add.
Determine the amount of sulfur you will need to lower your soil pH to a good growing level for your particular plants. Do this by using a university extension service or commercial chart or garden calculator. For most garden annuals, vegetables and perennials, your goal is to create neutral-to-slightly-acid soil, with a pH of 6.5 to 7.0.
Pour or rake the sulfur evenly over the entire planting area.
Turn soil, with the shovel or spade, to a depth of at least the length of the tool blade, mixing sulfur thoroughly with soil. Rake if necessary to break up clods of dirt.
Let the soil sit for at least one week and up to one month before planting. This lessens the danger of sulfur being converted by excess water into hydrogen sulfide, which is corrosive to plant roots and increases the opportunity for soil bacteria to convert sulfur into root-accessible sulfuric acid before you plant.
To Remedy Nutrient Deficiency
Test soil samples for the contents of soil minerals. According to North Carolina Extension soil specialist Jack Baird, sulfur is hard to measure because it travels quickly through levels of soil and is rapidly depleted by plants. Testing for mineral contents will, however, offer clues as to the form of sulfate fertilizer you choose, to simultaneously address other soil-mineral deficiencies.
Consult an extension or commercial chart to determine quantities of fertilizer you need to add to soil.
Pour or rake the fertilizer evenly over the soil.
Turn fertilizer into soil with spade or shovel, to a depth of the tool blade. Rake soil to smooth for planting.
Proceed with seeding or planting as convenient. Fertilizer is ready to act as soon as added to soil.
- Adding elemental sulfur or sulfate-based fertilizer is a spring garden chore. The bacterial conversion of elemental sulfur to sulfuric acid requires several weeks.
- Some plants, like rhododendrons and azaleas (Rhododendron spp.), varieties of which are hardy in U.S. Department of Agriculture plant hardiness zones 4 through 9, and rabbiteye blueberries (Vaccinium ashei), hardy in zones 7 through 9, have very specific requirements for acidic soil. For any new plant varieties, check pH needs before doing soil improvement.
- Like all fertilizers, sulfate-based ones need to be used in the amounts directed. Adding too much fertilizer can damage plants as much as adding too little.
Janet Beal has written for various websites, covering a variety of topics, including gardening, home, child development and cultural issues. Her work has appeared on early childhood education and consumer education websites. She has a Bachelor of Arts in English from Harvard University and a Master of Science in early childhood education from the College of New Rochelle.