Applying sulfur to lower soil pH

How it works

Soil bacteria convert elemental sulfur to sulfuric acid, which lowers pH. The process needs warm, moist soil and takes weeks to months, so results are gradual. Above about pH 7.5, iron and manganese become hard for grass to take up and the lawn yellows despite feeding.

Confirm first

Run a soil test. If the soil is chalky or full of limestone, sulfur barely moves the pH, because the carbonate neutralizes it as fast as it acts. On such soils choose grasses that tolerate alkaline conditions and use iron feeds for color instead.

How much and how

• Use the rate your test or soil lab recommends; on established lawns, no more than about 25–50 g/m² (½–1 lb per 100 sq ft) per application to avoid scorching.
• Apply in spring or autumn, when the soil is moist and not cold.
• Spread evenly, then water it in well.
• Repeat only after retesting, usually after several months.

Faster help for the color

While the pH slowly comes down, an iron sulfate feed greens the lawn within days.