Soil pH Levels for a Healthy Lawn

Acid or Alkaline?

Soil pH is a measure of its acidity and alkalinity. On a scale of 1-14, 1 is the most acid and 14 is the most alkaline; 7 is neutral, neither acid nor alkaline. The best pH for turf is between 6 ( a little acid) and 7.2 (slightly alkaline). Some soils are naturally alkaline but in most parts of Australia soils are more likely to be a bit acidic. What we add to soil, notably fertilisers, can change its pH. Lime raises the pH of soil, making it more alkaline, but other fertilisers tend to be acidic. Sulphate of ammonia, a fast acting fertiliser for lawns is highly acidic and its habitual use will lower soil pH over time. Other lawn foods are also acidic but not as strongly as sulphate of ammonia.

Why pH matters

When soil pH is outside its ideal for lawns, certain nutrients in the soil become harder for the grass plants to extract. The lawn may start to go yellow with thinner growth and no matter how much fertiliser you apply it has no effect on the lawn (and it could be making the pH problem worse).

How to Correct

If the soil is too acidic (that is, below a pH of 6), dust the lawn with agricultural lime and water it in. If the soil is too alkaline (above pH7.2) use powdered sulphur or sulphate of ammonia dissolved in water. Don’t be too enthusiastic in your application. It is much better to raise or lower pH in small steps about a month apart rather than in one big concentrated hit. After application, water the lawn well and continue to do so weekly. Test the soil again a month later when the application has had time to work.

How to Test

To test the pH of the soil, buy a pH test kit at the nursery. Follow directions in the kit. These kits are very easy to use, readily available and they could diagnose your lawn problem in just a few minutes.