My Soil Is Acidic — What Does That Mean for My Garden?

Acidic soil is one of the most common soil problems in gardens across the UK and northern Europe, especially on sandy ground or where rainfall is high. A soil pH below 6.0 creates an invisible barrier between your plants and the nutrients already present in the ground. Understanding what drives acidity — and how to correct it — is the first step toward turning a struggling plot into a productive one.

What Causes Soil Acidity?

Acidity builds up through several natural and human-driven processes. Heavy rainfall leaches calcium, magnesium, and potassium — alkaline minerals — out of the topsoil, leaving behind acidifying hydrogen ions. Decomposing organic matter releases organic acids as it breaks down. Conifer trees and oak drop acidic leaf litter. Repeated use of ammonium-based fertilisers acidifies soil over time as nitrogen transforms in the soil. Sandy soils with low buffering capacity acidify fastest, while clay and chalk soils resist the shift more effectively.

Signs Your Soil Is Too Acidic

Pale, stunted growth that does not respond to feeding is the most common sign. Phosphorus locks up below pH 6.0, so plants may show classic phosphorus deficiency symptoms — dark green or purplish leaves, poor root development — even when phosphorus levels are high. Moss and sorrel thrive in acidic conditions, so their presence in a bed or lawn is a useful biological indicator. Brassicas in acid soil are also highly vulnerable to clubroot, a devastating root disease. A simple pH test confirms what the plants are telling you.

Which Plants Tolerate or Prefer Acidity?

Not everything suffers in acidic soil. Blueberries, cranberries, and lingonberries require it, thriving between pH 4.5 and 5.5. Potatoes, strawberries, and sweet corn manage well in slightly acid ground around pH 5.5 to 6.0. Rhododendrons, azaleas, and heathers are classic acid-lovers in the ornamental garden. If you are growing these plants, maintaining acidity is the goal — adding lime would be counterproductive.

How to Correct Acidic Soil

Garden lime — ground calcium carbonate — is the standard corrective. Apply calcitic lime if magnesium is not deficient; dolomitic lime (which contains both calcium and magnesium) if your soil is deficient in both. The amount you need depends on how acidic the soil is and its texture: clay soils are highly buffered and need more lime than sandy ones to shift pH by the same amount. A rough guide is 200 to 400 g per square metre to raise pH by one unit in sandy soil; 300 to 600 g in loam; and 400 to 700 g in clay. Always test before applying and test again three months later. Autumn application is best, giving time to integrate before planting season.

Maintaining the Correct pH Long Term

Liming is not a one-time fix. Rainfall and organic matter continue to acidify soil, so a small maintenance dressing every three to five years is normal for most garden soils. Adding composted garden waste, avoiding ammonium sulphate fertilisers, and growing green manures all help buffer pH naturally. Once you hit the target range, regular retesting every two or three years is enough to stay ahead of the drift.