Topsoil is a fantastic resource for gardening. It’s far more fertile than subsoil, making it an ideal growing media for most plants. But how can tell topsoil apart from other types of soil?
Here are 6 ways to determine whether your soil is topsoil:
- The soil has a dark color.
- The soil has a loose consistency.
- The soil is granular when dry.
- The soil is rich in organic matter.
- The soil has a neutral or alkaline pH reading.
- The soil rests at the highest level of the ground.
Topsoil is essential for a healthy garden or harvest, and you should ensure that your growing media contains this vital ingredient. If you’re unsure whether the soil you’re working with is topsoil, you can review the following properties of topsoil to make an educated guess.
1. The Soil Has a Dark Color
One of the most reliable indicators of topsoil is a dark coloration varying between dark brown and black. Topsoil consists of several organic components, many of which contain dark-colored carbon compounds.
But color isn’t always a reliable indicator, as topsoil color can vary from place to place.
Soil Color Varies Depending on Location
While most topsoil is dark, topsoil coloration varies depending on location.
For example, naturally sandy terrains often feature lighter-colored topsoils that vary in color between yellow and gray. Those living in coastal, low-lying environments will likely encounter sandy topsoil. However, states with deserts are also likely to have sandy topsoil.
If you live in any of the following states, you may notice that the topsoil in your area is lighter in color than store-bought loamy topsoil:
- Arizona
- California
- Colorado
- Florida
- Nebraska
- New Mexico
- Utah.
The sandy topsoil typical throughout these areas can pose challenges to gardeners, especially those looking to grow non-native vegetables, flowers, herbs, and shrubs. Fortunately, you can amend sandy topsoil to make it more fertile.
2. The Soil Has a Loose Consistency
Try scooping your hand into the soil and splaying your fingers. If the soil falls gently through the gaps in your fingers, there’s a good chance you’re working with topsoil.
Recently excavated topsoil tends to have a loose consistency, mainly when dry. That’s because topsoil is typically more porous than dense subsoil. It contains tiny pockets (or pores) that keep the soil aerated. These soil pores help make topsoil lighter and looser than other types of earth.
However, there are a few factors that affect topsoil consistency. For example, topsoil with a high percentage of clay is often far denser than topsoil with equal parts sand and silt and a minimal amount of clay (called loam soil). Tamping and rainfall can also affect topsoil consistency.
Tamping Soil Can Make It Denser
Putting pressure on topsoil, either by walking on it or tamping it down, can make it denser.
So if you’re testing soil that’s been sitting beneath heavy pots and furniture (or that you often walk across), it may be denser than bagged topsoil purchased from gardening centers.
Water can also make topsoil more dense and compact. For that reason, it’s crucial to consider moisture levels and recent rainfall when determining whether the soil is topsoil.
Rainfall Can Affect Soil Consistency
Because topsoil typically features large pores that trap air and water, rainfall can significantly change the density and consistency of topsoil. As a result, wet topsoil may not be as loose as dry topsoil. As such, it’s best to examine the soil in question when it’s dry to ensure the soil’s real consistency.
3. The Soil Is Granular When Dry
Another indicator to watch for is soil texture. Topsoil tends to have a granular texture when dry, easily separating into small clumps or grains.
Subsoil tends to clump together into sticky, dense masses. This characteristic is especially true of clay subsoil. However, some types of subsoil can also form small grains when dry.
For example, sandy subsoil drains quickly and is composed of grains. That said, sandy soil is often lighter than topsoil, making it easy to tell them apart.
Still, soil texture is changeable, as gardeners can add sand, clay, or organic matter to change a soil’s type. But without direct human intervention, soil texture remains consistent.
The same theory applies to the levels of decayed organic matter found in soil—if the ground is left undisturbed, measuring the amount of organic matter present in the soil can be a helpful indicator of its type.
4. The Soil Is Rich in Organic Matter
Topsoil is the result of organic materials that die and decay. For this reason, topsoil tends to be rich in organic matter (called soil humus). This decaying organic matter imparts essential nutrients, making topsoil a fertile substance capable of helping plants grow healthy and strong.
But this nutrient-rich organic matter is often invisible to the naked eye. As organic components break down to form topsoil, they become a homogenous mixture.
This process also helps homemade compost transform from identifiable materials (rotten leaves, grass clippings, coffee grounds, etc.) into a single substance (fertile compost). Still, you may be able to spot organic matter in the process of decaying in areas where topsoil is present.
Types of Decayed Organic Matter Found in Topsoil
Several types of organic matter add nutrients to the topsoil. Some of the most common sources of soil humus include:
- Fallen leaves from trees and bushes
- Rotten twigs and branches
- Dead insects
- Fecal matter from animals and insects
- Decaying plants and fruits.
You can use a soil test kit to determine whether your soil sample is rich in nutrients. Most of these test kits also measure soil pH level, another indicator that you can use to determine whether a soil qualifies as topsoil.
5. The Soil Has a Neutral or Alkaline pH Reading
Loamy topsoil tends to have a neutral or basic pH level, meaning that it’s rarely acidic. If you’re attempting to determine whether a soil is topsoil or not, testing its pH level may help.
Testing Soil pH Level
Soil pH test kits are readily available from most plant nurseries and home improvement stores. These test kits typically contain multiple testing vials and chemicals to test for nitrogen, phosphorus, and potassium levels in the soil. These are the three most crucial nutrients that make the soil fertile.
Because topsoil is rich in decayed organic matter, it typically contains an adequate level of nutrients (40 ppm or more). It also tends to have a neutral pH reading (falling between 6 and 7).
Why pH Level Is Crucial to Growing Healthy Plants
Soil pH level significantly impacts soil fertility. Highly acidic soils may inhibit root growth, slow plant growth, or cause premature plant death.
Alternatively, highly alkaline soil can struggle to retain nutrients, leading to nutrition-related growth problems in plants. The most fertile topsoil tends to have a balanced pH level between 6 and 8.
Pesticides Can Change Topsoil pH
Pesticides can help gardeners keep unwanted pests and fungi away from their plants. However, pesticides can also alter topsoil pH, making pH one of the least reliable indicators of whether a soil sample is topsoil or subsoil.
Chemical pesticides can take years to degrade. In addition, those who’ve used pesticides in their garden may find that the pH of their topsoil is acidic, as many pesticides lower soil pH levels.
Natural pesticides (like vinegar) can also lead to a lower-than-average topsoil pH. Alternatively, other natural pesticides (like baking soda spray) can increase topsoil pH, making it more alkaline.
If you’ve used pesticides on or near the soil you’d like to test, it may be better to rely on other indicators to determine whether the soil in question is topsoil.
6. The Soil Rests at the Highest Level of the Ground
Topsoil gets its name because it sits at the highest level of the ground. So, for example, the soil beneath your lawn is topsoil.
If you’re not using store-bought topsoil, the uppermost five to ten inches (12.7 to 25.4 centimeters) of earth on your property is likely topsoil. But those living in mountainous areas or places with recent volcanic activity may find that topsoil only extends a few inches beneath the soil surface.
Areas with a prevalence of volcanic activity (like the Hawaiian Islands) may have vast regions that lack topsoil entirely, as one inch of topsoil takes approximately 500 years to form naturally.
Key Takeaways
Topsoil is typically rich in nutrients, making it a fantastic resource for gardeners. But telling the difference between topsoil and subsoil can be challenging if you’re unfamiliar with the qualities of topsoil.
Fortunately, there are several qualities you can look for that can help you determine whether the soil you’re working with is topsoil. Some of the most significant indicators include:
- Dark coloration
- Loose consistency
- A granular texture when dry
- Prevalence of decayed organic matter
- Neutral or basic pH level
- Sitting at the highest level of the ground.
If you want to learn more about improving soil quality, you can read my other article here: How to Improve Soil Quality (The Ultimate Guide)
