Soil pH in St. Mary, LA: Lime or Sulfur?
Typical topsoil pH in St. Mary, LA
Typical topsoil in St. Mary, LA is pH 6.52, already right for vegetable garden (6-7). Test before adding anything.
What St. Mary needs, by plant
- Already in range: lawn (cool-season grass), vegetable garden, tomatoes, roses.
- Just outside, test first: strawberries (off by 0), pink hydrangeas (off by 0).
- Sulfur: potatoes 3.4 lb/100 sq ft over 2 applications; blueberries 5.1 lb/100 sq ft over 3 applications; azaleas and rhododendrons 4.4 lb/100 sq ft over 3 applications; blue hydrangeas 4.4 lb/100 sq ft over 3 applications.
What to do next
If your test lands near 6.52, you can skip lime and sulfur for lawn (cool-season grass), vegetable garden, tomatoes, strawberries, roses, pink hydrangeas.
How mixed the soil is
Of the 347,832 surveyed acres in St. Mary, LA, 49% are near neutral (6.5-7.3), 25% are moderately acidic (5.5-6.5), 18% are alkaline (above 7.3), 8% are strongly acidic (below 5.5). Mapped soils run from pH 4 to 7.9, a spread of 3.9 units across 58 soil components. No single class covers 60% of the county, so two gardens a few miles apart here can need opposite treatments. Test your own bed.
Clay, organic matter and rates
Topsoil here averages 61.2% clay and 9.26% organic matter, which this site treats as clay. At 9.26% organic matter the soil buffers like a heavier one, which pushes it into the clay bracket. Moving it one pH unit takes about 11.5 lb of lime or 3.4 lb of sulfur per 100 sq ft. 14% of mapped components carry free carbonate (lime already in the ground).
St. Mary against the rest of Louisiana
pH 6.52 is 0.98 above the Louisiana median of 5.54. 55 of 64 Louisiana counties have more acidic topsoil. Nationally it is more alkaline than the US county median of 6.05.
Closest in pH within the state: Ascension (6.44), Assumption (6.44), Avoyelles (6.44), Iberia (6.49), St. Charles (6.53), Orleans (6.61), Plaquemines (6.71), St. James (6.76).
The range in Louisiana runs from Allen at 4.88 to St. Bernard at 7; St. Mary sits 77% of the way up.