How to test pH in soil: The complete guide

Published: 02 July 2023

Whether you're a hobby gardener or a farmer by trade, helping your plants to thrive is a vital way to increase your yield and improve the health of the flowers, vegetables and herbs you produce. One of the best ways to understand and improve your soil is by examining pH. pH soil testers provide valuable information that you can use to improve the quality and balance of your soil, giving you healthy, happy, high-producing plants.

This guide covers everything you'd ever want to know about soil and pH, from the very basics to how best to test soil pH with digital technology. Read on now to learn all about it:

What is soil?

On a basic level, we all know what soil is. It's the medium that allows plants to grow, providing the nutrients and water necessary to grow shoots, expand roots and reach towards the sun. Soil is the top layer of the earth, around 2 metres deep, and forms the primary layer where most plant life grows.

Soil is formed of three main components. These are:

  • Organic: the broken down materials and debris from animals, plants and other living organisms.
  • Inorganic: the non-organic materials that plants use to gain nutrients in the form of minerals, water and gases.
  • Microorganisms: the tiny life forms that exist within the soil, that break down the material and provide food for plants.

Soil is formed and altered by five main factors: climate, organisms, geology, topography and time. These individual factors play a significant role in soil healthiness, functionality and make-up, making it essential to consider where you'd like to plant and whether you need to bring in other soil or fertiliser to achieve success.

What is pH?

pH is a number that measures how basic (alkaline) or acidic a material or substance is. When you measure pH, you’re using a tool that provides a reading of the number of hydrogen atoms carrying a positive charge within your sample. pH is used to measure various materials and substances, from water to food products to soil.

The higher the concentration of hydrogen ions there are in a sample, the more acidic it is. On the other hand, a lower concentration makes a sample more basic. Something acidic, such as coffee or orange juice, will fall between 0-7 on the pH scale. If a substance is basic, such as household cleaners or baking soda, it will fall between 7-14. pH 7 is true neutral and is the pH of pure, filtered water.

a graph representing pH from 0-14, going from acidic to basic

Why test the pH of soil?

Testing the pH of soil is an excellent way to gain insight into a factor that can limit the growth and success of plants, whether that means sickly, slower-growing shoots or lower yield when harvest time arrives. By checking the pH of your soil against the ideal pH for that particular plant, you can adapt and adjust the pH in your soil to achieve optimal growing conditions.

Supplements and fertilisers are standard methods to improve soil pH and align it with the requirements of individual plants. By consistently measuring pH with a high-quality pH soil tester, you can quickly make changes to give your plants the best chance for healthy growth.

What affects soil pH?

Soil pH is affected by both natural environmental factors and artificial changes. Some of the factors to consider when you're planning to plant fruit, vegetables, or flowers include the following:

Climate and weather

Temperature, humidity, rain, sunlight and seasonal changes impact soil pH. High volumes of rain, for instance, can wash away essential nutrients that help plants to grow strong. Calcium carbonates are common basic nutrients found in most soil. If rain washes this nutrient way, the soil can become acidic.

When water comes into contact with decaying matter, like leaves, this can also cause changes in the pH as decomposing materials release carbon dioxide, which forms acid when mixed with rainwater. In climates with less rain, a lack of water can make the soil more alkaline, as fewer nutrients and minerals are being moved about, leading to higher concentrations.

Plants

The existing plants and ecology in an area can impact pH. Soil found beneath grass is typically more basic, while soil below trees leans more towards acidic thanks to the higher volume of decaying leaves. Not such a problem if you're building a raised garden bed, but more so if you're planning to use the soil you already have.

Irrigation

The water you use to keep your crops green and healthy can also impact the soil. Unless you're using pure, filtered water, your pH in your watering can or irrigation system will likely not be perfectly balanced. If your water is on the acidic side, this alters the pH of the soil, much like if your water is more alkaline (basic).

Soil type

The materials that make up your soil impact its overall pH. While most soil in the UK hovers around a natural, neutral pH of 7, this varies for areas with a less balance. For example, locations with high levels of chalk or limestone are more likely to be alkaline. Heathland and coniferous woodland areas are more likely to be acidic, by contrast.

The soil texture also impacts how difficult it is to change pH, known as 'buffering capacity'. Sandy soil has a low buffering capacity, while clay has a higher buffering capacity. The higher the buffering capacity, the more difficult it will be to change soil pH.

Fertiliser

Fertiliser is used for hobby gardens and industrial-scale farmland to improve yield by bringing in more essential nutrients and minerals. pH must be considered when choosing a fertiliser, as it can have an impact on the pH of the soil. Artificial fertiliser is more likely to lower pH, while organic fertiliser tends to cause an increase because of organic, soluble acids within its composition.

Nutrient availability

If the pH of soil is too low or too high, it's harder for plants to absorb all the nutrients they need to thrive. Calcium and phosphorus, two critical nutrients, can become bound up to other materials in the soil if the pH is off, leading to fewer nutrients for your plants. However, there isn't a catch-all for plant nutrients. With some plants preferring different pH levels, it's important to consider what they need individually to thrive.

Even though plants like different pH levels, some hard limits exist. A much too low pH can cause aluminium toxicity, poisoning plants with unbound aluminium in the soil. Similarly, a too-high pH will unbind iron in the soil, leading to yellowing and unhealthy plants. Molybdenum poisoning is also a risk in alkaline pH, leading to sad, stunted crops.

What are the optimal pH soil ranges for growing?

There's no such thing as a single, optimal pH range for all plants. For example, potatoes thrive at a pH of 4.5-6, while walnut trees prefer a pH of 6-8. Here are a few examples of the preferred pH for different flowers, vegetables and herbs to get you started:

Garden plants and flowers:

Plant Type

Preferred pH

Acacia

6-8

Acanthus

6-7

Amaranth

6-6.5

Bougainvillea

5.5-7.5

Dahlia

6-7.5

Erica

4.5-6

Euphorbia

6-7

Fuchsia

5.5-7.5

Gentian

5-7.5

Gladiolus

6-7

Hellebore

6-7.5

Hyacinth

6.5-7.5

Iris

5-6.5

Juniper

5-6.5

Lingstrum

5-7.5

Magnolia

5-6

Narcissus

6-8.5

Oleander

6-7.5

Paulownia

6-8

Portulaca

5.5-7.5

Primula

6-7.5

Rhododendron

5.4-6

Roses

5.5-7

Sedum

6-7.5

Sunflower

5-7

Tulip

6-7

Viola

5.5-6.5

Vegetables and herbs:

Plant Type

Preferred pH

Artichokes

6.5-7.5

Asparagus

6-8

Aubergines

5.5-7.5

Barley

6-7

Beans

6-7.5

Brussels Sprouts

6-7.5

Carrots

5.5-7

Cucumber

5.5-7.5

Lettuce

6-7

Maise

6-7.5

Oats

6-7

Onions

6-7

Peas

6-7.5

Peppers

6-7

Potatoes

4.5-6

Sweet Potatoes

5.5-6

Pumpkins

5.5-7.5

Spinach

6-7.5

Strawberries

5-7.5

String Beans

6-7.5

Tomatoes

5.5-6.5

Wheat

6-7

Adjusting soil pH with treatments

So, what can you do if your soil pH exceeds the required range for your seedlings or chosen crops? A few different options are available to help you restore pH to proper balance for your choice of plants:

Adjusting acidity

If the soil is too acidic, lime and calcium carbonate are two of the most common choices to improve soil pH. Ground-up eggshells are another option that many gardeners swear by to keep their plants healthy.

Adjusting alkalinity

Irrigation is one of the most effective ways of lowering soil pH, but it must be done in moderation to avoid over-watering your plants. Other than this method, you can also use gypsum, iron sulphate, sulphuric acid, or calcium chloride to restore balance.

TIP: The cost of materials and the available planting space will impact which solutions work best for you. What works for a small planter at home isn't cost-effective for a large-scale farming operation over multiple acres.

How to test soil pH

There are two different methods to test soil pH for planting. These consist of direct soil testing and slurry testing. Whichever method you prefer to use, it's vital that you take repeated tests and samples from the exact same spots and use the same processes every single time.

Direct soil pH testing

Direct soil testing involves using a suitable pH tester for soil in the location where you plant your crops. With this method, there's no need to take samples away, but you'll need to remember the exact testing locations so you can repeat your soil pH tests time and time again.

How to test with the direct soil method

The direct soil method for pH testing includes the following steps:

  1. Pick your testing locations, ideally several sample areas for variety and terrain.
  2. Rinse the testing probe with distilled or DI water.
  3. Ensure the soil is moist; avoid testing soil that's too dry or too saturated.
  4. Make a hole in the dirt with a ruler or auger for consistent testing depth.
  5. Insert the electrode into the soil and wait for your reading to stabilise.

Slurry soil pH testing

Slurry soil testing involves taking away soil samples from multiple testing areas and using those samples to get a general idea of a wider planting space. You need to take slurry samples from the same depth and location each time. If you have an extremely large planting space, like multiple fields, this method gives you a good idea of pH across the area through a simple testing process.

How to test with the slurry soil method

The slurry soil method for pH testing includes the following steps:

  1. Pick your testing locations, ideally several sample areas for variety and terrain, based on what you'd like to grow.
  2. Dig down to 6 to 8" with a trowel in your bed, ensuring visibly different samples are separated, and similar combined.
  3. Separate/combine in small buckets; mix well when combining multiple samples.
  4. Remove any larger debris from the mixture, including plant matter, rocks, and twigs.
  5. Choose a 1:1 or 1:2 ratio for all samples, ensuring consistency with the same ratio for every sample.
  6. Mix soil with distilled water in the chosen ratio. Keep separated samples apart during the measuring stage.
  7. Mix the slurry and allow it to stand for 15 minutes to settle.
  8. Remix and submerge the electrode within the slurry, waiting for the reading to stabilise.

What tools can you use to test soil pH?

pH test strips

pH test strips, or litmus paper, are the simplest thing you can use to test pH in soil. These paper strips are saturated with pH-sensitive dyes that change colour when exposed to a damp substance. It's quick and easy but not very reliable, making it a poor choice for anyone serious about gardening or looking to get the most out of their crops.

Because dirt is dark in colour, it's easy for this material to obscure results, leading to difficulty figuring out the exact pH. In addition, test strips usually have a 0.5 unit resolution for pH, which means the result at the upper or lower end of acceptable could actually be further than you’d expect.

Pros:

  • Affordable
  • Simple to use
  • Might work for hobbyists or beginners

Cons:

  • Not accurate to the highest degree
  • Relies on your reading the result accurately
  • Easily obscured by dirt

pH chemical test kits

Chemical test kits are a step above your traditional pH test strips. A chemical test kit for soil includes everything you need to check a sample. Instead of placing dirt on paper, you mix it in a tube with distilled or DI water and included chemicals. These chemicals react to provide a visual identifier of the pH within the soil sample.

pH test kits are often limited to specific pH ranges and have a lower resolution of 1-0.5 pH points. If you don't know your starting pH, buying multiple kits to get the desired results is be a costly process. You'll also need to repeatedly rebuy tests and dispose of chemicals appropriately once you've established the pH of the soil.

For example, our HI-3896 test kit includes 25 tests per kit, so you’ll need to invest further in the right chemicals and materials to continue testing once they run out.

Pros:

  • Easy to use
  • Relatively affordable for limited use
  • Suited to hobby and education

Cons:

  • Multiple kits are required for different ranges
  • More difficult to read than a digital screen
  • Limited tests per kit are often more expensive than a single digital pH tester

Pocket pH testers for soil

Pocket testers are, as the name suggests, pocket-size. These easily accessible digital testers give you full access to soil pH testing technology without the need to do all the work of figuring out the results yourself. A pH electrode in a durable casing gives the tester greater accuracy than strips or more labour-intensive testing kits, allowing you to read pH with a better resolution with a more affordable cost, particularly when it comes to the repurchase of consumables.

As we've covered above, soil pH testers allow you to test in the field, either with direct soil or slurry testing. Soil pH testers like the HI-98118 are also often waterproof and may feature anti-clogging technology to ensure your readings are accurate and consistent. As electrodes are affected by heat, inbuilt compensation in many testers helps to keep results steady and precise.

A digital soil pH tester like the HI-981030 takes the guesswork out of testing in comparison to the average chemical test kit or test strip. To achieve consistent accuracy, you'll want to ensure you're taking care of our pocket tester to achieve the best results. You can achieve this goal by using the correct solutions for calibration, hydration and cleaning. We cover how to care for pH electrodes in more detail below.

Pros:

  • More cost-effective for day-to-day use
  • Accurate, consistent results without the guesswork of test kits or strips
  • Works with both methods for testing soil pH

Cons:

  • Has a more expensive initial cost (but a good return on investment)
  • You’ll need to maintain your pH tester to continue to get accurate results
TIP: Some pH meters can also be used to read other measurements in the soil that are integral to healthy growth, such as electrical conductivity. Our HI-98131 Groline AGRIKIT soil tester is an excellent example of that.

Portable pH meters for soil

Portable pH meters bring your testing up a level, delivering laboratory-grade results in a handy, compact package you can carry anywhere. This portable technology makes your job easy for more serious operations, such as commercial and agriculture-based businesses. They deliver pinpoint, accurate results with resolutions as low as 0.0001 units for pH.

Many portable pH meters do more than your average pocket tester. For example, the HI-9814 does pH, conductivity and TDS all in one, saving time and effort while delivering exceptional accuracy. CAL Check is also inbuilt into our pH meters, enabling the meter to check the condition of the electrode and pH buffers in calibration, plus tutorials built right into the meter to make your job easier. One of these soil pH meters might be the best choice if you need to report on pH and provide laboratory-grade data.

Much like a pocket tester, a portable pH meter for soil requires care and maintenance to operate at its best. We’ve covered all the fundamentals for keeping your electrode clean, clear and in perfect working order below.

Pros:

  • The ideal choice for commercial and agricultural operations
  • Pinpoint accurate for pH
  • Inbuilt features for ease of use and consistency

Cons:

  • The most costly of the portable options
  • A little more technical than a standard pH tester
  • Maintenance and care needed

Permanent multiparameter monitors

If you'd like all the convenience of a multiparameter meter without the need to set it up and carry it around with you, opting for a permanent monitor is a viable solution. While these monitors are at the upper end of the price bracket, they are well worth the investment if you need a pH, EC, TDS and temperature meter to consistently keep tabs on your plants.

A permanent meter is a good fit if you have valuable or delicate plants that need careful, consistent management to grow and thrive. These meters are popular for greenhouses, hydroponics, and aquaponics, making them highly versatile for various purposes. Once placed, a permanent monitor does the rest of the work for you, allowing you to adjust and adapt quickly to any changes.

The HI-981420 is one example of a pH monitor that does it all for you. With results refreshing every 15 minutes, it’s possible to be notified as swiftly as possible of any changes in temperature, pH or conductivity that could affect the growth or health of your plants.

Pros:

  • Highly reliable and consistent for accurate readings
  • pH, conductivity, TDS and temperature in one
  • Alarms with LED indicator for fast response to changes

Cons:

  • Higher cost than a portable meter
  • Restricted to one area rather than moving between different locations
  • Requires more setup than a pocket or portable tester

How to care for your soil pH electrode

Taking care of your pH electrode is vital to ensure it lasts for as long as possible. A good routine is an excellent starting point for keeping your equipment in the best condition. Cleaning, calibrating and conditioning are the 'three Cs' you’ll want to remember for pH electrode maintenance.

1. Clean often

Thoroughly cleaning your pH electrode before and after you use it ensures it functions at 100% accuracy. When measuring soil, it's easy for residue and clumps to be left behind. If this happens, rinsing with distilled water is the best move.

Using an appropriate cleaning solution is the ideal choice for really stuck-on dirt. HI-700663P Cleaning Solution is designed specifically to work with soil, helping to remove all residue often found in agricultural samples. The cleaner your electrode is, the more accurate your results are. After cleaning, you should place your electrode in a storage solution for one hour before conducting other tests.

How to clean a pH electrode step-by-step

The steps for how to clean a pH electrode include:

  1. Fill a spray or squeeze bottle with distilled or deionised water
  2. Rinse the electrode gently using the water
  3. Gently shake the electrode, removing any residual droplets
  4. Use or store your electrode

To deep clean your electrode, follow these steps:

  1. Rinse with deionised or distilled water
  2. Allow the electrode to soak in a suitable cleaning solution
  3. Remove the electrode from the solution
  4. Re-rinse with distilled or deionised water
  5. Place electrode in storage solution for an hour before re-use

2. Calibrate for accuracy

Calibration helps you achieve the highest accuracy when testing for pH. By calibrating your electrode, you prevent changes in response over time, whether due to ageing or external factors. Calibrating to two pH points bracketing your expected pH value is highly recommended; one point above and below the expected ranges. For example, if you expect a reading of pH 8.5, you would use pH 7 and pH 10 buffers.

TIP: Daily calibration is highly recommended for accurate pH, but you can calibrate more infrequently if you don't need exceptional accuracy.

How to calibrate a pH electrode step-by-step

If you are using a single-use packet of pH buffer, follow these steps to calibrate your pH electrode:

  1. Rinse the electrode with deionised or distilled water
  2. Enter calibration mode on your pH soil meter
  3. Insert the electrode into the opened packet so the bulb and junction are covered
  4. Allow the reading to stabilise and accept the buffer solution
  5. Remove and rinse the electrode
  6. Repeat with any other pH buffers
  7. Exit calibration mode on completion

If you are using a bottle of pH buffer, follow these steps for pH electrode calibration:

  1. Pour the buffer into a clean beaker and place a magnetic stir bar in the solution
  2. Use a stir plate to ensure the buffer is continually stirring
  3. Enter calibration mode on your soil pH meter
  4. Insert the electrode into the beaker so the bulb and junction are covered
  5. Allow the reading to stabilise and accept the buffer solution
  6. Remove and rinse the electrode
  7. Repeat with any other pH buffers
  8. Exit calibration mode on completion
TIP: Using fresh pH buffers every time gives you the best possible results, with a much lower chance of contamination or ineffective electrode calibration.

3. Condition the electrode

The sensing bulb at the bottom of the electrode is one of the most essential components of your pH tester. This bulb is made from glass and is sensitive to hydrogen ions, maintaining equilibrium within the electrode to ensure stable readings by maintaining hydration.

Hydration is achieved by storing your electrode in a storage solution, like HI-70300L, when it's not in use. Keeping your electrode in other solutions, such as deionised or distilled water, can harm the bulb and lead to slow or inaccurate readings.

How to condition a pH electrode step-by-step

Follow these steps to condition your pH electrode:

  1. Rinse the electrode in deionised or distilled water
  2. Open the single-used sachet or prepare your beaker of storage solution
  3. Place the electrode in the conditioning solution, ensuring the junction and bulb are covered
  4. Leave the electrode in the conditioning solution for one hour or overnight to rehydrate
TIP: Improper storage leads to damage, but recovering a refillable electrode is possible. You'll need to fill it with fresh electrolytes and rehydrate it using a storage solution. While this doesn't work every time, it may be a handy tip to know.

Buy pH soil testers from Hanna Instruments UK

Hanna Instruments is the specialist for soil pH meters. Browse our full Groline range online today to discover pocket pH testers, permanent pH monitors and everything in between. Whether you're a gardening hobbyist or a skilled expert in agriculture, our technology is designed to help your plants to thrive.

Need advice before you buy a pH tester for soil? Contact our team directly; we'll help you find the best product for your goals.

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