- 1). Determine which material you want to use. Elemental sulfur, aluminum sulfate, iron sulfate and sulfur coated urea are all viable options, each with its own benefits and drawbacks. According to the University of Illinois Extension, aluminum sulfate should only be applied for hydrangeas; other plants may suffer from accompanying aluminum toxicity. Sulfur-coated urea causes a smaller change in pH and is thus easier to use without risking over-application; moreover, it also contains other plant nutrients and can thus be used as a fertilizer. Iron sulfate causes a more rapid change in pH than elemental sulfur but larger quantities are required for the same change in pH. Elemental sulfur is the most potent of these acidifying agents; although it takes months to change the soil pH with elemental sulfur, the resulting alteration can last for years.
- 2). Determine what the desired pH range for your plants will be. Keep in mind that you should only attempt to lower the soil pH if you already know its current value and the desired value (i.e., what pH range is optimal for the plant you want to grow).
- 3). Determine how much of the material you've chosen is needed to change pH to the desired level. If applying sulfur-coated urea, use it as a fertilizer and follow the manufacturer's instructions. For elemental sulfur, the correct amounts to apply are listed under the second link in the resources section below. If applying aluminum sulfate, apply roughly 6.9 times as much as you would elemental sulfur. If applying iron sulfate, apply roughly 6 times as much as you would elemental sulfur.
- 4). Take great care to avoid over-application. It's better to err on the side of caution than to apply too much and end up with a problem.
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