Key Takeaways
- Before adding amendments to improve soil, first carry out a simple jar test to work out what kind of soil you’re working with.
- A jar test is a simple, cheap and effective way to analyse your soil without the need for any fancy equipment or prior knowledge.
- To get the best results a jar test will need 2-7 days to settle – the longer you leave it the better.
- The Soil Texture Triangle is a free and useful tool for interpreting your results that many people don’t know about.
When it comes to growing anything at all in your garden, the thing I always tell my clients is that finding out the soil type you have is the single most important thing you can do. Soil type refers to the proportions of the three different-sized particles and main components that make up the soil: sand, silt, and clay. The percentage of each component determines what soil you have, and this determines the suitability for growing certain plants, fruits and vegetables. It also helps you determine the amendments required to improve problem soils. A simple jar test is the simplest way to find out what kind of soil you have.
Materials Needed for the Test
- Clear glass jar with a tight-fitting lid
- Ruler
- Pen & paper
- Soil sample from your garden
- Few drops of dishwashing liquid (optional)
How to Conduct the Experiment
- Fill your jar about one-third full with the garden soil
- Fill the remainder of the jar with water, leaving 3-4cm at the top.
- Add a few drops of dish soap (optional; helps separate the soil particles).
- Screw the lid on tightly and shake vigorously for 1-2 minutes.
- Place on a surface where you won’t need to move the jar for at least 48 hours.
Interpreting The Results: Sand, Silt, and Clay Layers
After letting the soil settle for 24-48 hours, you’ll start to see distinct layers. A lot of instructions online will tell you this can be done in 24-48 hours but I prefer to wait a week until the water at the top is almost clear. Then you can really see what’s what. The layers will have settled in the following order:
- Bottom: Sand (settles fastest)
- Middle: Silt
- Top: Clay (settles slowest)
- There may be some organic matter floating on top – you can ignore this.
Measure the height of each layer and the total height of all three layers. To calculate the percentages of each component, use this calculation:
Percentage of each component = (Height of layer ÷ Total soil height) × 100
Using the Soil Texture Triangle
Once you have calculated your percentages (they must add up to 100%), use the clay and sand percentages to plot your point:
- On the left side of the triangle, find your clay % and mark it.
- Draw a horizontal line straight across from that point (clay lines are horizontal).
- On the bottom side, find your sand % and mark it.
- Draw a line upward and diagonally to the left (following the direction of the lines that run from bottom-right toward top-left).
- Where these two lines cross = your soil type.
‘Loam’ is the ideal blend and what makes good quality topsoil. Obviously, you don’t need to go to the trouble of using the soil texture triangle to get a pretty good idea of your soil type, especially if you leave it for up to a week. I’m just a stickler for detail.
Common Mistakes to Avoid in Soil Testing
You can’t really go wrong with this DIY test, but should you get confusing results or are not able to see the distinct layers, check to make sure you haven’t made one of these common errors:
- Not shaking the jar vigorously enough (ensure the soil has broken up and there are no lumps once you’ve finished shaking).
- Not allowing sufficient settling time (clay particles take the longest – a week is preferable).
- Using the Soil Texture Triangle incorrectly – be sure that you are following the lines in the correct order and only using the clay and sand percentages – the silt will be determined by default.
Next Steps
I never start planning any growing area until I’ve carried out this simple jar test and I recommend you do the same. Once you understand the type of soil you’re working with you’ll be best prepared to start planning what will grow in your garden. If the answer turns out to be more organic matter, topsoil versus compost explains which of the two the job actually needs. Click here if you wan to find out how to improve the different soil types – and happy shaking!
If you would rather talk your soil through with a person, ring Outdoor Aggregates on 0330 043 7585. The office is open 7am to 7pm, seven days a week.
Have you ever done the jar test on your own soil? What did the layers come out like, and did the result surprise you? Tell us in the comments.
