How to Test Soil pH Levels

If you really want the flowers and vegetables in your garden to thrive, it is absolutely essential that you know your soil pH level. By knowing this you can then grown plants and produce that suit the environment or alter to suit those that you want to grow.

In this guide we take a close look at all things soil pH and what you need to do to identify and adjust it.

What is pH?

pH is a measure of how acidic or alkaline a substance is, with a scale ranging from 0 to 14. A pH of 7.0 is neutral, anything below (7 – 0) is acidic, and anything above is alkaline (7 -14).

Soil pH affects plant growth. Some plants thrive in acidic soil, while others prefer alkaline conditions. Understanding your soil’s pH helps you choose the right plants or adjust the soil for optimal growth.

In general, soil in soft water areas tends to be acidic, while soil in hard water areas is more alkaline. Soil type also gives clues: peaty soil is usually acidic, clay soil is neutral, and chalky soil is alkaline.

Why are pH Levels Important?

Each plant species has a preferred pH range for optimal growth. Some plants, like blueberries, prefer acidic soil (pH below 7), while others, like lavender, thrive in alkaline soil (pH above 7).

If the pH is too high or too low for a particular plant you are growing, it may struggle to absorb nutrients, resulting in poor growth, yellowing leaves, or even plant death.

By testing and adjusting soil pH, and researching the particular pH levels the plants you are growing prefers, you ensure your plants get the right conditions to flourish.

Soil pH also influences soil microbes, which play a key role in breaking down organic matter and making nutrients available to plants.

If the pH is too high or too low, the beneficial microbes in the soil may not function properly, leading to nutrient deficiencies or imbalances.

In addition, pH levels can impact water retention and drainage. Acidic soils tend to retain more water, while alkaline soils may drain faster.

So, with the above in mind, you can appreciate exactly why pH levels are so important as they have so much bearing on whether a garden fails or succeeds.

What Different Soil Types are There?

Aside form the different pH levels that soil can have it’s also important to know that there are also quite a few different types of soil, each with it’s own different characteristics you should be aware of, here are some of the most common:

Sandy Soil

Sandy soil is light, gritty, and drains quickly. It has large particles that allow air and water to flow through easily, which can be both an advantage and a disadvantage.

While this soil type is excellent for plants that need well-drained conditions, such as cacti or lavender, it can struggle to hold onto nutrients and water, which means plants may need more frequent watering and fertilising.

To improve sandy soil, you can mix in organic matter like compost or mulch. This will help retain moisture and nutrients for your plants.

Clay Soil

Clay soil is dense and sticky when wet, and it compacts easily. This soil type retains water and nutrients very well, but it can also become waterlogged, which may lead to root rot for some plants.

Clay soil can be difficult to work with, especially when it’s wet, but it can be improved by adding organic matter or sand to increase drainage and loosen the texture.

Clay soil is ideal for moisture-loving plants, such as willows or certain types of hydrangeas. However, for other plants, it may need to be amended for better aeration and drainage.

Loamy Soil

Loamy soil is often considered the “gold standard” for gardening because it contains a balanced mixture of sand, silt, and clay.

This soil type has good drainage, holds nutrients well, and is easy to work with. Loam is ideal for growing a wide variety of plants, including vegetables, flowers, and trees.

Most gardeners and landscapers prefer loamy soil because it supports healthy plant growth and requires minimal intervention.

To maintain loam, adding organic matter each year can keep the soil rich and fertile.

Silty Soil

Silty soil has fine particles and feels smooth to the touch. It can hold moisture better than sandy soil and is more fertile, but it can also become compacted and sticky when wet.

Silty soil is often rich in nutrients and supports a wide variety of plants, however, it may need better drainage if it becomes waterlogged, so adding organic material like compost can improve its structure.

Silty soil is great for growing a variety of vegetables and flowers, but like clay, it may require aeration to prevent water-logging.

Consider adding coarse sand or gravel to enhance its drainage.

Peaty Soil

Peaty soil contains a high amount of organic matter and moisture, giving it a spongy texture.

It is dark and rich in nutrients, which makes it excellent for growing certain plants like blueberries and cranberries, however, peaty soil can be acidic, so it’s important to monitor the pH levels if you’re growing plants that prefer a more neutral or alkaline environment.

Peaty soil is commonly found in boggy or wetland areas and is often used in gardening for acid-loving plants.

To optimise peaty soil for general use, mixing in some lime or other pH-neutral amendments may be necessary.

Chalky Soil

Chalky soil is alkaline and often contains lime, which gives it a slightly stony texture. It tends to be nutrient-rich, but its alkalinity can affect certain plants that prefer acidic conditions.

Some plants, like lilacs and certain vegetables, thrive in chalky soil, but others may struggle if the pH is too high.

If you have chalky soil, you may need to adjust its pH or choose plants that are suited for alkaline conditions, such as brassicas (cabbage family) or certain herbs like thyme and rosemary.

When is the Best Time to Test Soil pH Levels?

The ideal time to test your soil’s pH is when the soil is moist, but not overly wet. While you can technically test soil pH at any time of the year, there are a few specific times that yield the most accurate and useful results:

Early Spring

Testing your soil pH in early spring, before you plant, is one of the best times to get accurate results.

At this time, the soil is typically moist from rain (mostly in the UK) or melting snow, which makes it easier for the pH testing material to penetrate. By testing in early spring, you have plenty of time to amend the soil if necessary.

If your soil is too acidic or too alkaline for your desired plants, you can adjust it by adding lime (to raise pH) or sulfur (to lower pH) well before planting season begins.

Autumn

Another great time to test your soil pH is in the autumn, after any plants have been harvested.

By this time, the soil has had the entire growing season to absorb nutrients, and testing at this time gives you a clear idea of what the soil needs to prepare for the next planting season.

Autumn testing also gives you time to amend the soil with lime or sulfur before the ground freezes, ensuring everything is ready for the next growing season.

Routine Soil Maintenance

Soil pH can fluctuate over time, especially after heavy rains, dry periods, or the addition of fertilizers.

For this reason, testing your soil pH once every 1-2 years is a must to ensure a productive garden.

Even if you don’t plan to plant right away, routine testing helps you monitor changes in your soil and make adjustments as needed.

If you’re maintaining a garden or lawn, testing the soil’s pH periodically will help you avoid nutrient deficiencies or toxicities that may arise from extreme pH imbalances.

How to Test Soil pH Levels: A Step-by-Step Guide

Testing your soil’s pH is easy and can be done in several ways. Here follows a quick run down on each method and then details on how each is performed.

Step 1: Choose Your Testing Method

There are three main ways to test soil pH: using a pH testing kit, a digital pH meter, or sending your sample to a lab. Each method has its pros and cons:

• Soil pH Test Kit: These kits are affordable and widely available from garden centres or online. They usually include test strips or a colour-coded solution that reacts with your soil sample. While not as precise as a digital meter, they give quick and reliable results for home gardeners.
• Digital pH Meter: This tool gives more accurate and faster results than a test kit. It’s a bit more expensive, but it’s a one-time investment that can last for many years.
• Soil Testing Lab: For the most accurate and detailed results, you can send a sample to a professional lab. This option may provide additional information, such as nutrient levels and soil texture, but it takes longer and can cost more.

Step 2: Gather Your Soil Sample

To get an accurate pH reading, you need a representative soil sample:

• Choose Multiple Locations: For larger gardens, take samples from different areas to get an average pH. For smaller spaces, one sample should suffice.
• Dig to the Right Depth: Use a clean trowel or soil auger to collect soil from 3 to 4 inches deep. This is the root zone where most plants’ pH is most impactful.
• Mix the Samples: If you’re collecting multiple samples, mix them in a clean container to get an overall reading of your garden’s soil.

Step 3: Test the Soil pH

Once you’ve gathered your soil sample, follow the instructions for your chosen testing method:

• For Test Kits: Add the soil to the provided container, mix with the testing solution, and compare the resulting colour to the included pH chart included in the kit.
• For Digital Meters: Insert the probe into the soil (following the manufacturer’s instructions) and wait for the digital reading to stabilise.
• For Lab Testing: Send your sample to the lab in the provided container etc. packaged as they request and wait for the results. This may take a few days to a week.

What the Results of pH Tests Mean

Your soil’s pH level directly affects which plants will thrive. Here’s a quick guide to what different pH levels mean for your garden:

• Acidic Soil: If your soil is acidic (low pH), it’s perfect for lime-hating plants like rhododendrons, azaleas, camellias, and heathers.
• Neutral Soil: Neutral pH is ideal for most plants, though it’s not suitable for those that hate lime, such as the plants listed above.
• Alkaline Soil: Alkaline soil (high pH) suits wildflowers like poppies, chamomile, and cornflower. Herbs such as bay, lavender, and rosemary also thrive here.

If your soil’s pH isn’t ideal for certain plants, you can make small adjustments. For example, adding lime to acid soil helps grow brassicas, while well-rotted manure, sulfur or aluminum sulfate can improve alkaline soil.

After amending the soil, retest in a few weeks to check that your adjustments have had the desired effect.

However, altering the pH across your entire garden is expensive and time-consuming. Instead, focus on growing plants suited to your soil in the ground, and use pots or raised beds for those that aren’t.

As you can see from the above, testing and confirming your soil pH level is absolutely essential to ensure that the plants, flowers and veg that you choose to grow, do indeed grow and thrive, and only by testing and knowing this can you be absolutely sure.