Why pH Deserves a Test Before You Spend a Penny

Soil pH is simply a measure of how acid or alkaline your ground is, running from about 4 (very acid) to 8 or 9 (very alkaline), with 7 sitting neutral. It matters because pH controls which nutrients plants can actually take up. Get it badly wrong and even a well-fed, well-watered shrub will sulk: leaves yellow between the veins, growth stalls, and flowers simply fail to appear.

Here in the UK, our rainfall is a natural soil acidifier. The wetter, cooler west and north tend to have acid soils, while limestone and chalk districts of the south and east push the other way. That is why a rhododendron that romps away in a Welsh valley can look half-dead on a Wiltshire chalk bank. Before you fall for a beautiful acid-lover at the garden centre, find out what your soil is actually doing.

What Different Plants Really Want

Most garden plants are easy-going, thriving in a neutral to slightly acid soil somewhere between pH 6.0 and 7.0. Hardy evergreens are no different — choisya, mahonia, photinia, osmanthus, skimmia and most hebes will settle happily in that comfortable middle ground.

The fussy ones sit at the extremes:

• Acid-lovers (pH 4.5–5.5): rhododendrons, azaleas, camellias, pieris, kalmia, blueberries, and most heathers including Calluna and winter-flowering Erica.
• Slightly acid (pH 5.5–6.5): Japanese maples, magnolias, ferns, most hydrangeas.
• Alkaline-tolerant (pH 7.0–8.0): lavender, buddleja, clematis, brassicas, lilac, and many hedging plants.

Notice how many of our best hardy evergreens — rhododendron, pieris, camellia, kalmia — are acid-lovers. In a cold-climate garden they earn their place with year-round structure, so it is worth getting the soil right for them.

Testing Your Soil Properly

Skip the cheap two-pronged probe meters; they are notoriously inaccurate. A simple colour-comparison kit from a garden centre costs very little and gives you a usable reading.

• Take samples in autumn or spring, when the soil is moist but not waterlogged.
• Dig ten to twelve small cores from across the bed, each about 10–15cm deep, and mix them in a clean bucket.
• Test a separate sample for each distinct area — the border by the wall may differ sharply from the veg patch.
• Follow the kit instructions exactly, using distilled or rainwater rather than tap water.

You can also read the weeds. Sorrel, foxgloves, bracken and heather suggest acid ground. Where campion, cow parsley, clover and field scabious grow well, you are likely nearer neutral or alkaline. It is rough, but it is a useful cross-check.

Retest every two or three years, and always after liming or adding sulphur.

Adjusting the pH — Gently Does It

Only adjust if a test tells you to. Chasing a number you have not measured is a waste of money and can harm your soil.

To make soil more acid: use elemental sulphur, worked into the top 15cm at roughly 70g per square metre to lower the pH by about half a point on light soil — up to three times that on heavy clay. It is slow work, taking three to six months, so apply in autumn for planting the following spring. Ericaceous compost, pine bark mulch and ammonium sulphate fertiliser all help nudge things along.

To make soil more alkaline: apply garden lime or dolomitic lime at around 200–500g per square metre, again in autumn or early spring, and water it in. Dolomitic lime also supplies magnesium.

Never lime and sulphur the same bed in one season — you will simply cancel yourself out. Go slowly, retest, and add a little more rather than overcorrecting.

The Sensible Alternative: Work With What You Have

If your soil is stubbornly chalky and you long for acid-loving evergreens, stop fighting it. Grow them in containers or a raised bed filled with ericaceous compost, which gives you complete control. Water with rainwater wherever possible — tap water in hard-water areas is alkaline and will slowly push the pH back up.

In the open ground, match the plant to the site. On alkaline soil, plant lavender, choisya, skimmia and mahonia instead. A hardy evergreen that suits your soil will outshine a struggling one every single time.

A five-minute test now saves a fortune in replacements later — and gives your acid-lovers the best possible start.