Soil Testing and Amending: What a pH Reading Tells You

By Growing Home Greens Team · July 31, 2026

Soil pH matters because it controls how available nutrients already in the soil are to a plant’s roots, a soil can be rich in nitrogen, phosphorus, and potassium and still starve a plant if the pH locks those nutrients into a form roots can’t take up. Most vegetables want a pH between 6.0 and 7.0, where the widest range of nutrients stays accessible.

Reading the number

Below 6.0, soil is acidic, and nutrients like phosphorus and calcium become harder for roots to absorb even when they’re present in the soil. Above 7.0, soil is alkaline, and micronutrients like iron and manganese are the ones that get locked up, often showing up as yellowing between leaf veins on otherwise healthy-looking plants. A home soil test kit gives a reasonable pH reading for a few dollars; a lab test through a local extension office costs more but adds nutrient levels the home kits don’t measure.

Fixing acidic soil

Garden lime (crushed limestone) raises pH gradually over a few months, which is why it’s worked into soil in fall for a bed that’ll be planted in spring rather than added right before planting expecting an immediate change. Wood ash does the same thing faster but less predictably, since the exact alkalinity varies by what was burned.

Fixing alkaline soil

Elemental sulfur lowers pH, also gradually, by feeding soil bacteria that convert it to sulfuric acid over weeks. Compost and other organic matter nudge pH toward neutral from either direction over time as a side effect of adding organic acids, which is part of why building organic matter into a bed generally simplifies pH management even when it isn’t the primary goal.

Skipping the test isn’t always a problem

Most bagged garden soil and raised-bed blends, like a standard Square Foot Gardening mix of compost, peat or coir, and vermiculite, start out in the ideal pH range without any amending needed. Testing matters most for native, in-ground soil that hasn’t been managed before, or when a bed’s plants are consistently underperforming despite good watering and light. Retest every year or two rather than once and never again, since amendments and rainfall both shift pH gradually over seasons.

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Soil Testing and Amending: What a pH Reading Tells You: A pH number is only useful once you know what it's telling your plants' roots. Here's how to read one and what to do about it.

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