This article covers the basic principles and methods of soil testing along with an overview of the various testing kits and their benefits and drawbacks.
Surprisingly, many home growers don’t undertake any soil testing, which is a shame as it can reveal problems and help them how to grow better plants with greater pest and disease resistance along with better crop yields.
Soil Testing
Article in brief and what I use
This is quite a long piece, so I’ll start with my basic recommendations and you can read through the article for my reasoning, detailed suggestions and some alternatives, if you have time.
When taking on a new plot, test the soil for nutrients (NPK) and pH (acidity). A month or two after initially adding fertiliser or lime, recheck. Thereafter, just check the pH annually.
It’s most cost-effective to use a good chemical test kit for NPK levels and a decent electronic meter to check pH levels. I use this Lustre Leaf kit for chemical testing and this Mcbazel meter for pH testing. (Links to Amazon)
Soil testing enables the grower to precisely provide the nutrients plants need without wasting fertiliser and spot deficiencies. It also enables the grower to provide the optimum pH level, which improves the availability of those nutrients.
Soil testing used to be an expensive process undertaken in laboratories but nowadays inexpensive, easy to use tests allow the home grower to measure the pH and the major nutrients – nitrogen, phosphorus and potassium – without sending soil samples away.
The micro-nutrients, basically the soil vitamins, are vital but unlikely to be critically short in soil which composts and manures are regularly added. Testing for these micro-nutrients is still the province of the professional laboratories.
What you must test for
Lime is the one thing you absolutely must test for. If the soil pH is too low, acid, or too high, it reduces the nutrient availability to the plants. Even if those major nutrients are abundant in the soil, with an out of range pH, they’ll be of little or no benefit to the plants.
Remember some plants, like leafy brassicas, want a high pH to really thrive, and the high pH helps to suppress club root. Others, like cranberries, have evolved to take advantage of acid conditions and prefer a low pH. The ericaceous, acid loving, plants will not do well in high pH soils.
Testing for the major nutrients, NPK, is useful. For example, crops like leafy brassicas or lettuce need large amounts of nitrogen to produce those leaves. Legumes, however, like an environment rich in potash to produce their best.
Having said that, assuming the pH is correct and the soil is in good heart, having been given manure or compost and, or, general fertiliser, then it should provide the needed nutrients.
It’s rare that a plot will be short of a micro-nutrient, but if you suspect a specific shortage, then it may be worth sending soil samples away to be tested. Having said that, it will be more cost-effective to just apply a general micro-nutrient boost with a specialist fertiliser like organically approved S-Chelate Cultiv-8
See Trace Elements for a list of micro-nutrients and symptoms of deficiencies. Worthy of special mention because it is a common problem when growing tomatoes is Magnesium See also: Tomatoes Magnesium Deficiency
When to Test
When starting a new plot or garden, testing for both pH and NPK nutrient levels makes sense. Usually a gardener will know the soil type in a general sense, but soils can vary widely over a short distance. For example, I have seen allotments that straddled the boundary of clay and sandy soils.
If a plot looks fertile with luscious green growth, it would seem reasonable to assume the nutrient level to be good. Despite that, it may be it is rich in nitrogen but low in potassium. A full test will reveal that and enable the required amendment to be made.
Following an amendment, be it fertiliser or liming to correct a low pH, allow a month or two and test again. This will show if, for example, enough lime was added to bring the pH into the desired range.
With pH levels, test the new plot again after a year. This will give a guide as to how quickly a soil is acidifying or moving towards alkaline. Generally, with liming, once every three or four years is sufficient. Testing shows if that is the case with your area.
With an established plot, testing every five or six years is worthwhile. Perhaps not so much for nutrient levels but certainly for acidity.
How to test
Soil can vary across a plot or garden, levels of nutrients and pH can vary over short distances. Perhaps the soil was fertilised and a handful was dropped in one place. Testing there alone will show a very nutrient rich plot although the rest of the plot may be deficient.
To allow for that, take multiple samples and test them. For a bed, take four samples from near the corners of the rectangle and one or two from the centre. Tabulate the results and discard any outliers.
Example test results table (pH)
- Sample 1 – 6.00
- Sample 2 – 5.50
- Sample 3 – 5.70
- Sample 4 – 6.20
- Sample 5 – 4.30
- Sample 6 – 6.20
In that example, Sample 5 is very low. You could confirm the test with a fresh sample from near the same point or just exclude the result. Add the remaining results together and take the average to give a fair estimate of the average pH. In this case the pH is about 5.9 generally.
When taking a sample, try to take it from about 5 cm down or lower. If sampling a lawn, lift the turf and then take the sample. That will be more accurate than the surface layer.
Results Range
It’s frustrating, we all want a definite, absolute result, but nature isn’t digital or absolute. In a way, electronic testers are too accurate. The results may appear definite – pH 6.2 – but a chemical test with a colour chart forces us to accept the results are a little fuzzy!
Testing Kits and Meters
Putting the search term ‘soil testing kits’ in on Amazon will result in 24 pages of kits, near 700! The price ranges from £2.06 to £1892.38, confusing to put it mildly. The top priced kit is designed for professional agronomists and the cheapest is basically some litmus papers.
There are basically two types of soil testing kit, chemical and electronic. Some years ago, I tried an electronic tester but it was very inaccurate. Happily, technology has moved on and the better meters are as accurate as the chemical test kits.
Let’s start by looking at the chemical kits. All the kits mentioned are to be found on Amazon. Prices are correct at time of writing (November 2025) but do not include any delivery costs.
Chemical Testing
Chemical tests all require soil samples to be taken and processed. The processes do vary but they all take some time to react and give a result.
Xlux pH Testing Kit
Xlux Soil pH Test Kit
I looked at this testing kit, which only tests the pH level. The soil sample is collected, added to a test tube and mixed with distilled water. This is left to stand for 30 to 60 minutes and a drops of the liquid placed on the pads of the test strips. This is left for a few minutes to develop, and then the colour of the pads are compared to a colour chart.
This provides a fairly accurate measure of the acidity level, but it takes around an hour per sample for a result. The kit comes with 200 test papers, 3 mixing tubes and 6 droppers. It does require distilled water for mixing as tap water would affect the results.
The kit costs £12.99. Add in 1.5 litres of distilled water per 50 tests at £5.49. You can save on the distilled water by buying larger amounts but 50 tests is quite a lot in one season! Cost per test: 37p
Luster Leaf Soil Testing Kit
Luster Leaf Products 1663 80 Professional Soil Test Kit
This is actually the test kit I have. It tests for the major nutrients, NPK and for pH. The kit contains enough reagents to undertake 20 tests per nutrient or for pH. Lustre Leaf have a good reputation, they also market the Rapitest kits which have been in garden centres for years. However, their electronic meters get some poor reviews for accuracy.
The tests differ between what is being tested for, but they’re all fairly quick to undertake and the results – as best as I can judge – fairly accurate.
One drawback, once a reagent is opened it should be used within 12 months. Basically this kit will allow you one season’s testing. Replacement reagents may be available, my supplier went out of business and Amazon don’t appear to offer them. However, for £34.66 seems a reasonable price for a good initial picture of the soil nutrients and pH level on the plot. Cost per test: 43p
Luster Leaf Products 1663 80 Professional Soil Test Kit
Electronic Testing
Over the years I’ve purchased a couple of electronic pH testing meters. Both were the analog type with a swinging needle indicator. Neither were accurate and the indicator had to be looked at whilst in position. Removing the meter from the soil to look at the meter wasn’t an option. A hands and knees job!
Soil test meter circuits
Apparently, the reason the cheaper analog meters often don’t give accurate pH readings is they may not use a true pH electrode — they often use a simplified galvanic cell that reacts to hydrogen ion activity, giving approximate results. And no, I don’t know what that means, either!
My Old Analog pH Meter
My old analog meter, in the photo, also indicates moisture and light levels. Moisture levels might be useful with pot plants but I’ve never found it necessary with garden soil. Even in a heatwave, my Mark 1 finger does the job. Light levels isn’t much value outdoors either, although helpful if growing indoors or with grow lights.
I think they add these things because it’s easy and makes the product look more versatile, rather than thinking people will need these additional functions.
Mcbazel 5-in-1 Soil Tester with Backlit LCD, Dual Probe
Soil Test Meter
This is the tester I purchased. It gives a fast result, within 10 seconds and is great for taking multiple readings. It appears pretty accurate as far as I can tell. Results from the large pots with ericaceous soil were 5.0 to 5.3 and a recently limed bed showed pH readings between 6.8 and 7.2, except for one outlier at 4.0. I cleaned the probes and that jumped to 7.0
It has a backlit display which helps with reading but the screen is vertical so even trickier to read in the soil than the old meter where the display was angled. However, once it has taken the reading, the meter can be removed from the soil and lifted to read. You have to be quick, though. The automatic switch off is a bit keen!
As well as pH, it also measures moisture and light levels along with temperature and soil fertility. Temperature can be useful in the spring when sowing or planting.
The soil fertility reading is very approximate, it’s not a direct measure of NPK (nitrogen, phosphorus, potassium). It’s just based on the electrical conductivity (EC) of the soil as compared with a factory preset baseline. That baseline varies depending on the type of soil, clay, sand, loam have very different EC baselines.
High EC can also result from salts (like sodium chloride), not nutrients. Temperature and moisture will also affect readings. So, the “fertility” reading is more of a general indicator of ionic activity than a precise nutrient analysis. In the absence of a proper NPK test, a good guide.
The testing meter costs £18.99 plus 3 AAA batteries. You can do as many tests as you like, the only running cost being batteries.
Mcbazel 5-in-1 Soil Tester with Backlit LCD, Dual Probe
NPK + pH Testing Meters
I looked at a number of electronic meters that test NPK as well as pH etc. These cost in the region of £140.00 and upwards. How accurate or reliable they are, I don’t know. Unknown brands whose name is a random collection of letters, do not instil confidence!
