How to Test Your Soil's pH (and Why It Matters More Than You Think)
If a plant is yellowing, stunted, or simply refusing to thrive despite seemingly good care, soil pH is one of the first things worth checking. It's an easy factor to overlook because it's invisible, but it quietly controls how well plants can actually access the nutrients already in your soil.
What pH Actually Means for Plants
Soil pH is a measure of how acidic or alkaline your soil is, on a scale from 0 to 14, with 7 being neutral. Most vegetables and garden plants prefer a slightly acidic to neutral range, roughly 6.0 to 7.0, because that's where the majority of nutrients remain most easily available to plant roots.
Outside that comfortable range, nutrients can become "locked up" in forms plants struggle to absorb, even if they're technically present in the soil in plenty. That's why a plant can show classic nutrient deficiency symptoms even in soil that's actually rich in nutrients — the pH is simply preventing the roots from taking them up.
Testing Your Soil
You don't need a laboratory to get a useful reading. Inexpensive testing kits, available from most garden centres, use a simple colour-change reaction: mix a soil sample with the supplied solution and compare the resulting colour to a chart. They're not laboratory-precise, but they're more than accurate enough for garden decision-making.
Electronic pH meters, which you push directly into moist soil, are another straightforward option and can be reused indefinitely. For the most accurate results either way, take samples from several spots around the area you're testing, since pH can genuinely vary from one bed to the next, and avoid testing immediately after adding fertiliser or lime, which can skew the reading.
Reading the Results
A reading below 6.0 indicates acidic soil, which particular plants like blueberries, rhododendrons, and camellias actively prefer. A reading between 6.0 and 7.5 covers the sweet spot most vegetables, lawns, and general garden plants are happiest in. Above 7.5 indicates alkaline soil, which some plants tolerate well but which can cause deficiency issues in others, particularly with iron and manganese uptake.
Adjusting Acidic Soil
If your soil tests too acidic for what you want to grow, garden lime is the standard fix. Applied according to the packet instructions and worked into the top few inches of soil, it gradually raises pH over several weeks. It's worth retesting a season later rather than repeatedly adding lime, since overcorrecting creates the opposite problem.
Adjusting Alkaline Soil
Lowering pH is generally slower and more gradual. Well-rotted organic matter, composted bark, and mulches made from pine needles or leaf mould all nudge soil gently towards acidity over time as they break down. Elemental sulphur is a more direct option for stubbornly alkaline soil, but it works slowly and is best applied well ahead of planting, ideally the season before.
Working With What You've Got
Sometimes the simplest answer isn't to fight your soil's natural pH at all, but to choose plants suited to it. Rather than repeatedly amending naturally alkaline soil to grow acid-loving plants like blueberries, many gardeners find it far less effort to grow those specific plants in containers filled with ericaceous compost, while planting the open ground with species that are naturally happy in alkaline conditions.
Retesting Over Time
Soil pH isn't fixed forever — rainfall, added materials, and what you've been growing can all shift it gradually over the years. Testing once a year, ideally at the same time of year for consistency, gives you an early warning if conditions are drifting away from what your plants need, long before problems become visible in the foliage.