Correcting pH with lime or sulfur
If the test was outside 6.0–7.0, work lime or sulfur into the topsoil now. It is far more effective than dusting the surface later.
- When
- In order, while the lawn is being made
- Material
- garden lime if acidic, or elemental sulfur if alkaline
- For
- Any lawn
- Rule
- est-amend-ph · Hessayon; RHS; Regional
If the test was outside 6.0–7.0, work lime (raises pH) or sulfur (lowers it) into the topsoil now — far more effective than dusting the surface after the lawn is in.
Lime for acidic soil
Below about pH 6.0, grass struggles to take up nutrients and moss gains ground. Garden lime (calcium carbonate) raises pH. Ground limestone is slow and gentle; dolomitic lime also adds magnesium. The amount depends on how far off the reading is and on the soil type: clay and soils rich in organic matter need more than sand to move the same distance. Use the rate your test kit or soil lab recommends.
Sulfur for alkaline soil
Above about pH 7.0–7.5, iron and other trace nutrients get locked up and the grass yellows. Elemental sulfur lowers pH as soil bacteria convert it, which takes weeks to months and works faster in warm, moist soil. Lowering pH is slower and harder than raising it, and chalky soils resist it; choose grasses that tolerate it instead of fighting the soil.
How
- Spread evenly and work it into the top 10–15 cm (4–6 in) while the soil is still open, before leveling.
- Do not apply lime and a nitrogen fertilizer at the same time; leave a couple of weeks between them.
- Retest after a few months, and before adding more.
See also: how to take a soil pH test.
Do this first
Sources
- D.G. Hessayon — The Lawn Experthessayon
- Royal Horticultural Society — lawn guidancerhs
- Regional practice — continental climate, zone 7regional