It’s good to know what you’re working with in terms of soil texture and structure. There’s a simple home test you can do to determine what type of soil you have in your garden, called the soil sedimentation test. It will tell you the percentages of sand, silt, and clay that you have in your soil. These percentages can then be used to find the overall soil type via the soil texture triangle chart at the end of this post.
Why is this important? Well, the soil texture can tell you a few things about your soil. For example, clay is able to hold helpful nutrients in the soil, and exchange them with plants. Sand and silt do not have this capability. So even though many gardeners tend to groan at the thought of clay in the soil, it’s actually a very useful component of soil and can help you grow nutritious food if it’s treated right. Because of its high nutrient-holding capacity, you can add more amendments than if you had a sandy soil (as long as you add the right ones!). Sandy soil doesn’t hold nutrients nearly as well, so it would be a waste to spend money on amendments that will just be washed away in the next rainfall.
To find out your soil’s texture:
Fill a 1L mason jar 1/3 full with soil.
Add cold water until the jar is 3/4 full.
Add 5 tablespoons of liquid dish soap.
Screw the lid on tight and shake vigorously for 10-15 minutes.
Set the jar down and wait at least an hour, but preferably overnight.
You will see banding in the jar as the layers of sand, silt, and clay separate. Measure the height of the sediment in the bottom of the jar, then measure the height of each different section to determine the percentages of each. This will tell you what type of soil you have when you chart it. In this case, I had 4.5 cm of sediment at the bottom of the jar. Find each percentage on the chart below, and draw a line straight through the triangle at each of the percentages. Where they intersect in the triangle will tell you what type of soil you have. For example, if you have 60% sand, 30% silt, and 40% clay, the area where they intersect is labelled ‘sandy loam’. That’s the description of your soil type.
Analyzing Your Soil
Once you know the type of soil you have, you will know more about the water holding capacity, air supply, and nutrient holding capacity of your soil.
Water is held in the soil by nature of the distance between the soil particles as well as the total surface area of the particles. The greater the surface area, the more water can adhere to the particles. Water’s two important properties, adhesion (to minerals and other particles) and cohesion (to itself), cause it to be held in the soil. Silt has a smaller particle size than sand, so it will hold more water due to the smaller particles having a greater surface area if compared to the same quantity of sand. It’s a larger particle size than clay, so it will give up water more readily. To recap: Clay = excellent water holding capacity, sometimes too good because it won’t give it up to plants. Silt = great water holding capacity, AND it will share more readily with plants because it doesn’t hold the water as tightly as clay. Sand = poor water holding capacity. Water tends to run right through sand, and if your soil has a high sand content, it will behave very similarly.
Pore space is the space between particles of soil. It tells us about the air supply to plant roots. The larger the pore space, the more air can reach the plant roots. Silt has a moderate level of air content. The pore space between particles is larger than with clay soils, but smaller than with sand. The water will drain out of pores when the force of gravity is greater than the force of cohesion (see above), leaving air behind. The large particles of sand create large pores that allow for good air flow, and the small particles of silt create small pores for air flow through the soil. Clay has much smaller particles, which doesn’t leave as much room for air to flow to plant roots. This also relates to compaction – if a soil is highly compacted, it will have very poor air supply due to the compression of the particles.
As already mentioned, clay is a superstar when it comes to holding nutrients in the soil, particularly positively charged nutrients like calcium and magnesium and potassium. That’s because clay has a negative electrical charge. Sand and silt do not have this capability. So the higher the clay content of your soil, the more nutrients it can hold. The sedimentation test will not tell you what kind of nutrients you have in your soil, or if indeed you have any. The negative charges in your clay might be filled with hydrogen, in which case you will have a very acidic soil. The only way to know for sure what’s in your soil is to get it tested at a lab. But, you at least know that you have the capability of holding good nutrition if you know you have a high clay content.
If you’re interested in testing your soil for nutrients (sending a sample away to a lab) and receiving a full analysis, I’m happy to offer my services.
– organic recommendations by me – Sarah Hemingway
– tested by SGS Laboratories
– find out exactly what your soil needs for balanced nutrition
– only add what’s missing
– full nutrition in the soil = full nutrition in the food you grow and eat
Please contact me (LINK) for more information.