Mineral amendments

Sulphur

Sulphur used as an amendment is available in powder (micronized sulphur) or granular form. It is used to acidify soil. Sulphur has a medium- and long-term effect on soil. This means that it should be applied one or two years before planting. For established plants, spread the recommended amount on the soil at the drip line and work it into the top 7 or 8 centimetres.

Sulphur may be applied in spring or fall, depending on your soil test results. If you need to apply large amounts, do so in two stages, once in early spring and then again in fall.

Granular sulphur works more slowly than powdered sulphur, but is longer-lasting. It is also easier to apply, leaches out of the soil more slowly and produces less dust. Inhaling sulphur powder may irritate respiratory passages.

Iron sulphate is very useful for lowering soil pH quickly, especially when plants show signs of an iron deficiency. How much you should apply depends on your soil test results. Its effects on soil are not as long-lasting as those of sulphur.

Aluminum sulphate is another way to lower soil pH. Ideally, this amendment should be used only with blue hydrangeas (Hydrangea macrophylla), because aluminum is toxic to many plants. How much you should apply depends on your soil test results.