How to Read and Interpret a Soil Test

Testing your soil can help you determine if there are any nutrient excesses or deficiencies. Too many nutrients, or not enough, can have a negative impact on the health and quality of your garden veggies. Doing a test can help guide you in the right direction as you make decisions about soil amendments that will help your plants grow better. 

You can also do a soil test for pH, which can help you amend the soil for specific plants. For example, azaleas and rhododendrons like acidic soil, but most other plants prefer a neutral pH balance. 

soil test interpretation guide mother nature

While the interpretation of a soil test might seem daunting, it is not as difficult as it might seem. The kits you can buy at the garden centre contain test tubes and capsules of chemical powder for each different nutrient of the common three, nitrogen, phosphorus, and potassium. To use these kits, you’ll need distilled water and soil samples from your garden

When the soil, water, and capsule powder are mixed up, they will change colour. The soil test kit will include a colour guide. Compare the tube to the guide to determine what level your soil nutrients are at. 

soil test interpretation guide mother nature

Collecting Soil Samples

If you’re testing the soil in a small area, like around your azalea bush, the test will usually suggest that you put a small portion of soil straight into the test tube. If you’re doing a general sample from your entire garden, you’ll need to collect samples from several parts of your garden and mix them together. 

For spot tests, collect a small sample of soil for the test tube from a depth of 3-4 inches. If possible, avoid touching the soil with your hands to avoid contaminating the sample. 

For an overall test, collect equal amounts of soil (1-2 tablespoons is plenty) from a depth of 3-4 inches from several locations around your garden. If your test kit wants you to use dry soil, then do your best to mix all of it up together, breaking down chunks with a clean utensil.

soil test interpretation guide mother nature

If your kit requires you to mix the whole batch of soil with distilled water first, make sure you shake it up really well to mix everything and let it settle until the water is as clear as possible. Sometimes this may mean leaving it overnight or even longer. This will also show you the different particles in your soil as it settles in layers. 

If you’re going to take samples from several places, like for your azaleas and rhododendrons, as well as your garden patch, label each sample, so you don’t mix them up. Painters tape is a quick and easy way to do this. 

Follow the instructions from your soil sampling kit. The instructions will tell you how much soil and distilled water to add to your test tubes and then the capsule. Once all the ingredients are in the tube, cap it and shake it really well. The liquid in the tube may start to change colour immediately, let the colour develop for several minutes, and then compare it to the colour guide included in your kit. 

soil test interpretation guide mother nature

How to Interpret a Soil Test

The colour chart in your soil test kit will help you interpret the results of your tests. There will be separate colour charts for pH, nitrogen, phosphorus, and potassium. A pH test will have a spectrum, usually dark green for alkaline and bright red for acidic, with yellow as neutral in the middle. 

The colour charts for nitrogen, phosphorus, and potassium will usually be more of a gradient. Very pale colours mean that there are very low levels of the nutrient in your soil, and very dark colours will mean there may be an excess of those nutrients in your soil.

The secret is almost always in the soil, so before you start adding to your garden this year, stop by for a quick visit at Mother Nature and grab yourself a soil test. Once you know what’s going on in there, you’ll have a much better understanding of your garden overall – whether it was thriving or struggling the year before. And, if you’re still feeling a little unsure about interpreting your first soil test, we’d be happy to give you a hand!