The soil under your lawn feeds your grass, shrubs and trees, and over time, important nutrients become depleted, affecting the health of your grass and other plants.
In addition, your soil’s pH level may become too acidic or too alkaline to support healthy growth. Testing your soil gives you detailed information, so you can feed your grass, shrubs and trees the balanced diet they need for optimum health.
Soil Test Basics
Always test your soil before laying new sod and before planting new trees or shrubs. For established lawns and landscapes, the rule of thumb is to test every two to three years before fertilizing in the spring.
Home testing kits are available at home and garden centers, but for a small fee, you can send soil samples through your local extension service for thorough testing and expert recommendations.
The extension service will respond with a report listing the amounts of nutrients, such as nitrogen (N), phosphorous (P), potassium (K), calcium (Ca), magnesium (Mg), zinc (Zn) and manganese (Mn), as well as pH levels for your samples.
The report will also include suggestions for amendments, so you can add specific formulations of fertilizer and lime or peat to enrich your soil.
Where to Sample
Separate the samples for distinct zones of your yard. For example, your yard might get mainly full to partial sun but have a wooded area in one corner and a low-lying section that tends to stay damp in another.
Each of these zones has distinct conditions that may require different amendments, so use a separate mixing container and a separate sample bag for each zone.
For a quarter to half acre lawn, you’ll want to collect two or three samples from each side of the house—for example, three from each side yard, three from the front and three from the back, for a total of nine. It’s important to zigzag around the yard so that some samples originate closer to the house, some from farther out and others in between.
How to sample your soil
- Request soil sample bags from your local extension service, one for each zone you’ve designated. If your lawn has similar conditions throughout, you’ll only need one sample bag.
- Dirty tools and containers can contaminate your samples. Even trace amounts of fertilizer or lime can skew your results, so start by thoroughly cleaning your trowel or shovel and use only fresh plastic containers, never metal.
- Using a shovel or trowel, clear all grass, thatch and mulch from the soil surface where you plan to dig.
- When testing soil for new or existing sod, dig a hole 4″ deep.
For shrubs and trees, dig a 6″ hole.
- Cut a slice of dirt along the side of the hole, approximately 1/4″ thick, 2″ wide and 4″ or 6″ deep. Place the soil in a clean plastic container.
- Once all the samples have been collected from a particular zone, mix the soil together thoroughly.
- Spread out approximately three cups of the mixed soil on a flat surface lined with clean white paper. (You’ll only need two cups, but it will shrink as it dries.) Allow the soil to air dry overnight.
- Pour two cups of the dried soil into the sample bag provided by the extension office, and mark the bag to identify the zone.
- Repeat steps 3 through 8 for each zone of your yard, using a separate container for each or thoroughly cleaning the container between zones.
- Take the soil sample(s) to your extension office and wait for the results.
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