How to Test Soil pH -at Home or in the Garden

Why Soil pH Matters

Soil pH is a measure of how acidic or alkaline your soil is, and it plays a major role in plant health. pH affects the availability of nutrients, the activity of microbes, and how well plants can absorb water. If the pH is too high or too low for what you’re growing, even nutrient-rich soil can fail to support healthy growth. Testing soil pH helps you choose the right plants, correct imbalances, and improve growing conditions.

In the UK, most garden plants thrive in soil with a pH between 6.0 and 7.0. Acid-loving plants like rhododendrons, camellias, and blueberries prefer lower pH, while others such as lavender and clematis tolerate more alkaline conditions.

Using a Soil pH Test Kit

One of the easiest ways to test your soil is with a soil pH test kit, available from most garden centres or online. These kits typically include test tubes, a colour chart, and a reactive solution or powder. To use one, take a small soil sample from your garden, usually from 10–15 centimetres below the surface. Remove stones, roots, or debris, and mix the soil thoroughly.

Add a measured amount of soil to the test container, add the testing solution or powder as directed, then mix with distilled water. After a few minutes, the liquid will change colour. Compare this to the colour chart provided to get your soil’s pH reading. This method gives a clear, practical result that helps you understand whether your soil is neutral, acidic, or alkaline.

Testing Soil pH with a Digital pH Meter

Digital soil pH meters are another option and offer quick, repeatable readings without chemicals or mess. To get accurate results, the meter’s probe must be inserted into moist, loose soil. If your soil is too dry or compacted, the reading may be unreliable. It’s a good idea to take several readings from different parts of your garden to get a more accurate average.

Digital meters require calibration and regular cleaning to stay accurate, but they’re ideal if you plan to test soil regularly or across multiple sites. Some models also test moisture and light levels, making them a versatile tool for gardeners.

The Vinegar and Bicarbonate Test (Home Method)

If you don’t have a test kit, there’s a basic home method that gives a rough idea of soil pH. Take two small samples of soil and place them into separate containers. Add vinegar to one. If it fizzes, the soil is likely alkaline. Add a little water and bicarbonate of soda to the second. If this fizzes, the soil is probably acidic. If there’s little or no reaction in either, the soil may be neutral.

While this method doesn’t give a precise reading, it can point you in the right direction if you're trying to decide whether to amend the soil or choose suitable plants.

Where and When to Test

Soil pH can vary across your garden, especially in raised beds, under trees, or where compost or lime has been applied. For best results, test several areas and take samples from a consistent depth. Avoid testing right after heavy rain or fertiliser application, as this can temporarily alter pH levels.

Testing is best done in spring or autumn when the soil is stable. Once you understand your pH, you can adjust it if needed or choose plants that naturally suit your conditions.

Understanding Your Results

A pH of 7.0 is neutral. Anything below that is acidic, and anything above is alkaline. Most vegetables, lawns, and general garden plants prefer a slightly acidic to neutral pH. If your soil is strongly acidic (below 5.5), you may need to apply lime to raise the pH. If it’s too alkaline (above 7.5), adding organic matter, sulphur, or using ericaceous compost can help lower it gradually.

Rather than chasing a perfect number, the key is to keep your soil within a range that suits your plants. Healthy, biologically active soil will usually balance itself over time with good care.

Soil pH Can Vary Within the Same Garden

It’s common for different areas of the same garden to have different pH levels, especially if you’ve added compost, fertiliser, or lime at different times. Tree roots, decomposing leaves, and shaded vs. sun-exposed areas can all subtly shift the chemistry of the soil.

For that reason, testing in multiple locations gives a clearer picture. Take samples from vegetable beds, flower borders, lawn areas, and any problematic spots where plants are struggling. This helps you spot patterns and apply pH adjustments only where needed — rather than altering the whole garden unnecessarily.

Combine pH Testing with Soil Texture Assessment

pH alone doesn’t tell the full story. Combine your pH testing with a basic soil texture test — feel the soil when moist. Is it gritty (sandy), smooth (silty), or sticky (clay)? Heavier clay soils hold on to pH adjustments longer, while sandy soils shift more easily and often need more frequent pH management.

Understanding both chemical (pH) and physical (texture) properties helps you make better choices when it comes to amending, fertilising, or planting.

pH Affects Nutrient Availability

Your soil pH isn’t just a number — it controls how easily nutrients are absorbed by plants. In acidic soils, elements like iron and manganese are more available, but phosphorus and calcium may become limited. In alkaline soils, iron, zinc, and manganese availability drops, which often leads to leaf yellowing (chlorosis) in sensitive plants.

Even if your soil is rich in nutrients, the wrong pH can block them, which is why your plants might still appear weak or pale despite feeding. That’s why pH testing is one of the first things to do when diagnosing poor growth.

Lab Testing for More Accurate Results

For professional or high-precision needs, send a sample to a lab for testing. Some UK labs and universities offer detailed soil analysis services for a modest fee. In addition to pH, they can assess organic matter, texture, nutrient levels, salinity, and even trace minerals. This is ideal for larger gardens, allotments, orchards, or landscaping projects where you want to build a long-term soil improvement plan.

While home kits are useful, lab tests provide a more complete snapshot of what’s happening beneath the surface.

Re-Test After Making Adjustments

If you’ve applied lime to raise the pH or sulphur-based products to lower it, don’t assume the change is immediate or permanent. It can take weeks or months for amendments to affect the entire soil profile, especially in clay-heavy soils. Re-test your soil after one growing season to monitor the effects and avoid overcorrecting.

pH changes gradually and needs maintaining over time — especially in high-rainfall areas, where leaching can push soil back toward acidity.

Final Word

Testing soil pH is a simple but powerful step towards healthier plants and better gardening results. Whether you use a kit, a meter, or a basic home method, knowing your soil’s pH gives you the knowledge to choose the right plants, make informed amendments, and improve soil performance. With regular testing and thoughtful management, your garden will be better balanced, more productive, and easier to maintain.