Know Your Soil, Soil Profile

Know Your Soil? Soil Profile, Soil Triangle, & Mason Jar Test

What’s a Soil Triangle you ask, and why is knowing this important? The cornerstone of healthy plants that thrive is understanding your soil type. First, let’s talk about the three sides of the Soil Triangle: Sand, Silt, and Clay. Too much of one of these three will make your job as a gardener a bit more difficult. Don’t despair, there are plants and watering techniques for each. Here is the description of each soil texture: sand, silt, and clay. Below the 3 soil textures is a Soil Triangle Diagram and information on soil texture classes.

Sand – Mineral particles of soil greater than .05 mm in diameter. Some can be as large as 2.0 mm. When moistened, sand feels rough when rubbed between the thumb and fingers. Most sand particles can be seen without a magnifying glass. When doing a soil test, sand will settle out first, usually with in the first minute.

Silt – Soil particles .002 to .05 mm in diameter. When wet, silt feels smooth, but not slick or sticky. When dry, silt is still smooth and if pressed between the thumb and finger will retain an imprint. Silt particles cannot usually be seen by the naked eye. When doing a soil test silt will settle out second, around 2 hours.

Clay – Soil particles less than .002 mm in diameter. When wet, clay becomes slick and sticky. When dry, clay is hard, and it will hold the form into which it is molded. Clay particles cannot be seen with the naked eye. When doing the soil test, clay will settle out last, after the water has cleared (around 24-hour mark).


Soil Texture Triangle

Soil Texture Classes

Soil textures are grouped into 12 classes (see diagram above) Each class indicates relative amounts of sand, silt, and clay.  This can be checked by a laboratory particle size analysis. A common home mason jar texture test can quickly tell what percentages of sand, silt, and clay are in your soil.

The ratio of particle sizes affects the amount of pore space — the space between the mineral particles — and therefore the amount of air and water a soil can hold. It also affects other characteristics. The smaller the soil particles, for example, the more they bind together when wet. Thus, clay soils can be sticky and difficult to work. They drain poorly and have less pore space for air, so roots may suffer from a lack of oxygen. However, clay soils are often rich in plant nutrients. In contrast, sandy soils can drain water too quickly for healthy plant growth and tend to be low in nutrients, but they are easier to work. Adding organic material can offset many of the problems associated with either extreme.

While there's no such thing as a perfect soil, different plants grow best in different types of soil. Most common garden plants prefer loam — soils with a balance of different-sized mineral particles (approximately 40% sand, 40% silt, and 20% clay) with ample organic matter and pore space. However, some plants grow better in sandy soils, while others are well-adapted to clay soils.

Mason Jar Soil Triangle Test

Mason Jar Test

It is best to collect small shovels of soil from around your garden and mix in a large bowl. This will give you an “average sample” for your garden. 

  1. Sift the soil to remove organic debris. 

  2. Using a mason jar, fill it to 1/4 it’s capacity with your sifted soil. 

  3. Add water to the mason jar so it is 3/4 full. 

  4. Add a few drops of dish soap (this will help keep the particles from sticking to each other. 

  5. With the lid tight, shake the jar thoroughly. Set the jar and do not disturb. 

  6. Soil particles will settle out by size:

  1. Sand mark level on the jar after 1 minute.

  2. Silt mark level on the jar around 2 hours.

  3. Clay mark level on the jar after water has cleared (around 24 hours).

  1. Ignore any floating organic debris.

  2. Measure the thickness of each layer individually and the overall thickness of the material in the jar (easiest by milometers).

  3. And measure the thickness of the material in the jar (easiest by milometers).

  4. Calculate the percentage of sand, silt, and clay.

  5. Individual layer thickness divided by the total thickness = percentage of each sand, silt, and clay.

  6. Where the three lines meet on the Soil Triangle diagram is the type of soil texture class that is in your garden.


By knowing your soil profile percentages, you can choose the plants that have adapted to your garden’s soil type. Pick plants that are right for your USDA Plant Hardiness Zone.


Other things to think about when picking plants for your garden areas: How much water does this plant require daily/weekly? Do I want to plant annuals (plants that have a one-season life cycle) or perennials (plants that live and overwinter for many seasons, typically as long as USDA Zoning guidelines are followed) Is my garden area in full sun, part sun, or shade? How big will the plant be at maturity? Is this plant deer or other critter resistant? What are the best plants to attract hummingbirds and pollinators? What are the bloom dates and duration for this plant? Do I need to deadhead spent blooms? Remember there are all types of plants for every level of gardener from those who prefer a low maintenance garden to the gung-ho full-time gardener. 


Those looking for more information related to horticulture, contact your county or state extension office. Here in Billings Montana the phone number for our extension office is 406-256-2828.