Soil pH Guide: Acidic vs. Alkaline—Testing, Adjusting & Plant Preferences

Soil pH controls nutrient availability. Most ornamentals and edibles thrive in slightly acidic to neutral soil (pH 6.0–7.0), but specialists demand extremes.

Understanding the pH Scale

• Logarithmic: pH 6 is 10× more acidic than 7; pH 5 is 100×.
• Neutral = 7.0. Below = acidic. Above = alkaline.
• Test with home kit (colorimetric) or lab (most accurate).

What Shifts pH

• Organic matter decomposition → acids
• Fertilizers (ammonium-based acidify; lime alkalizes)
• Water quality, mulch, rainfall, temperature

Plant pH Preferences

Adjusting pH Safely

To Acidify (Lower pH)

• Peat moss / leaf mold / sawdust: Slow, safe, improves soil structure. Mix into planting hole + top-dress.
• Aluminum sulfate: Fast-acting. Max 1 lb/100 sq ft per application; retest. Overuse = toxicity.
• Elemental sulfur: Slower, gentler, microbial conversion.

To Alkalize (Raise pH)

• Garden lime (calcitic/dolomitic): Standard. Rate per soil test.
• Wood ash: Fast, adds potassium. Use sparingly—excess = salt buildup.

Amend gradually. Retest in 3–6 months. Sudden shifts shock roots and soil life.