Soil is the upper layer of earth in which plants grow; a black or dark brown material typically consisting of a mixture of organic remains, clay, and rock particles.
The University of Arizona further defines effective soil depth for plant growth as the “vertical distance into the soil from the surface to a layer that essentially stops the downward growth of plant roots.”
This depth tends to decrease in zones close to the poles and increase in zones near the equator.
To fully evaluate the soil conditions in your garden you need to get a shovel, and then select a safe site for digging a 2-3 foot hole. Look for particles (e.g. largest to smallest; coarse sand, medium sand, fine sand, silt, and clay), structure (vertical), consistency (resistance to breaking down depending on the moisture content), permeability (ability to move water through the soil), and chemistry (e.g. acidity and alkalinity; azaleas like acidic soil and chicory prefers alkaline soil).
You may wish to first identify your site on a soil classification map in order to get a general idea of what to expect. For instance, in the southern part of the county where I live there is everything from fine clay to coarse sand. But remember, micro conditions in your garden can be much different from the overall patterns.
Below is a step by step approach to evaluating the soils in your garden.
Rounding Up Supplies
You will need the following:
- Measuring tape
- Notebook for recording
- Ziplock bags (sample collection)
- 2 small bowls
- ½ cup of vinegar
- ½ cup of water
- ½ cup of baking soda
- watch with second hand
- 5-10 cups of water (for permeability test)
Soil Testing Procedure
Begin by creating 5 summary charts such as the following:
Then, before you dig, conduct appropriate surface tests (pH level and permeability) and record results for:
- Size of particles: classify them as coarse sand, medium sand, fine sand, silt, and clay.
- Consistency: classify the dirt as wet, moist or dry.
- Color: classify the dirt as brown, grey etc.
- pH level: alkaline or acidic (see below for instructions) Note: Only do this at the 2 foot level!
- Permeability: ability to move water through soil. Note: Test this last! To do this, pour 5-10 cups of water on the undisturbed ground directly beside the hole and record the amount of time it takes to filter out into the bottom of the hole, if at all.
Continue with the other levels.
Directions for Easy at-home Soil pH Test
To find out whether the soil is alkaline or acidic, do the following:
- Scoop some soil from the two-foot-depth into a container. Then, add a half-cup of vinegar. If the soil bubbles or fizzes, it’s alkaline.
- If there’s no reaction, scoop a fresh soil sample into a second container. Add a half-cup of water and mix. Then, add a half-cup of baking soda. If the soil bubbles or fizzes, the soil is highly acidic.
Completing the Soil Evaluation
You might want to take some pictures after all this effort; but remember to apply what you find to the selection and care of your plants. Happy gardening.