Getting the Dirt on Soil Testing

Jun 18, 2024

Soil testing is a helpful practice for gardeners aiming to achieve healthy plant growth and a bountiful harvest. Understanding the composition of your garden soil helps tailor gardening practices to meet the specific needs of your plants. This article provides an overview of laboratory soil testing, covering its importance, the key elements tested, how to collect a soil sample, and how to interpret the results.

Why Soil Testing is Important

Soil testing is valuable for several reasons:

  • Nutrient Management: It provides detailed information about the nutrient content of the soil, enabling gardeners to apply the correct type and amount of fertilizer.
  • pH Level Adjustment: Knowing the soil's pH level, which affects nutrient availability, allows gardeners to adjust it to the optimal range for their plants.
  • Detecting Contaminants: Tests can reveal the presence of harmful contaminants like lead or other heavy metals, ensuring the safety of your garden produce.
  • Cost Efficiency: By applying only the necessary fertilizers and amendments, gardeners can save money and prevent environmental pollution.
  • Tailored Gardening Practices: Understanding soil health helps in making informed decisions, leading to better plant growth and yield.
  • Troubleshoot Why Plants Aren't Thriving: If you've exhausted your attempts to amend soil with compost, a soil test can provide more detailed information to remedy the problem.

Key Elements Tested in Soil

A standard soil test can include analysis of the following elements:

  • pH Level: Indicates the acidity or alkalinity of the soil.
  • Macronutrients: Such as nitrogen (N), phosphorus (P), and potassium (K), which are crucial for plant growth.
  • Micronutrients: Including elements like iron (Fe), manganese (Mn), and zinc (Zn), which plants need in smaller amounts.
  • Organic Matter Content: Affects soil structure, nutrient availability, and water retention.
  • Cation Exchange Capacity (CEC): Reflects the soil's ability to hold onto essential nutrients.

Placing soil sample in test tube
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Collecting a Soil Sample

To obtain accurate soil test results, most labs will have specific instructions to follow. In general, These are the steps for collecting a soil sample:

  • Choose the Right Time: The best time for soil sampling is when the soil is moist but not wet, typically in the spring or fall.
  • Select the Area: If your garden has distinct areas with different crops, soil types, or problem spots, sample each area separately.
  • Collect the Sample: Use a clean tool to take small amounts of soil from several spots within the sampling area. Mix these samples in a clean container to create a composite sample.
  • Depth of Sampling: For lawns and gardens, a depth of 6-8 inches is appropriate. For trees and shrubs, sample at a depth of 6-12 inches.

Soil samples shown in a lab setting
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Interpreting Soil Test Results

Soil test results will provide detailed information about the elements mentioned above. Here's how to interpret some of the key findings:

  • pH Level: Most garden plants thrive in a pH range of 6.0 to 7.0. Values outside this range may require the application of lime (to raise pH) or sulfur (to lower pH).
  • Nutrient Levels: The report will indicate whether nutrient levels are low, medium, high, or excessive. Low or medium levels suggest the need for supplementation, while high or excessive levels mean you should cut back on those nutrients.
  • Recommendations: Most soil tests come with recommendations for amendments and fertilizers. Follow these guidelines to adjust nutrient levels and pH accordingly.

Soil testing is a powerful tool that empowers gardeners to make informed decisions about managing their garden soil. By understanding the specific needs of your soil, you can optimize plant health, improve yields, and contribute to the sustainability of your gardening practices. Whether you are a hobbyist or a professional gardener, soil testing is a practice that yields long-term benefits for your garden and the environment.

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Resources

Analytic Testing Laboratories for Home Gardeners

Soils, Water, Plants, Heavy Metals and More

  • Contact the labs to confirm offered services, pricing and preferred procedures for sample collection.
  • Testing labs vary in the types of available tests and recommendations they provide, if any. Be sure to ask for detailed information regarding tests, test fees and interpretation, and whether recommendations are included. Many of the websites provide supplemental information about tests and sampling.
  • Resources regarding soils and soil testing:

A & L Western Laboratories, Inc.

1311 Woodland Avenue, Suite 1

Modesto, CA 95351

(209)529-4080

http://www.al-labs-west.com/

Test descriptions and fees available online.

  • Soil 

  • Water

  • Plant tissue (nutrient testing only)

  • Fertilizer/Compost

  • Metal Analysis, including lead

California Laboratory Services

3249 Fitgerald Road

Rancho Cordova, CA 95742

(800) 638-7301

www.californialab.com

Test descriptions and fees available online.

  • Soil 

  • Water

  • Plant tissue (nutrient testing only)

  • Fertilizer/Compost

  • Metal Analysis, including lead

Control Laboratories, Inc.

42 Hangar Way

Watsonville, CA 95076

(831)724-5422

http://www.controllabs.com/

Test descriptions and fees available online under shipping info.

  • Soil 

  • Water

  • Plant tissue (nutrient testing only)

  • Compost

Dellavalle Laboratory, Inc.

1910 W McKinley Ave., Ste. 110

Fresno, CA 93728

(800)228-9896

http://www.dellavallelab.com/

Test descriptions and fees available online. Call / email for fees.

  • Soil 

  • Water

  • Plant tissue (nutrient testing only)

  • Plant Diagnostics

  • Fertilizer/Compost

Fruit Growers Laboratory Inc

2500 Stagecoach Rd

Stockton, CA 95215

(209) 942-0182

www.fglinc.com

Test descriptions and fees available online.

  • Soil 

  • Water

  • Plant tissue (nutrient testing only)

  • Fertilizer/Compost

  • Metal Analysis, including lead

Harmony Farm Supply & Nursery

3244 Gravenstein Highway North

Sebastapol, CA 95472

http://harmonyfarm.com

(707) 823-9125

Call for test availability, description and fees.

https://www.harmonyfarm.com/services/

  • Soil 

  • Water

  • Plant tissue (plant petiole – nutrient testing)

Peaceful Valley Farm & Garden Supply

125 Clydesdale Court

Grass Valley, CA 95945

(888)784-1722

https://www.groworganic.com/

Test descriptions and fees online.

  • Soil

Videos of explanation of professional soil testing & results:

https://www.groworganic.com/organic-gardening/videos/

Professional soil testing:

https://www.groworganic.com/soil-health/soil-testing.html

Perry Laboratory

424 Airport Blvd 

Watsonville, CA 95076 

(831)722-7606

www.perrylaboratory.com/   

Test descriptions and fees available online.

  • Soil 

  • Water

  • Plant tissue (nutrient testing)

Wallace Laboratories

365 Coral Circle 

El Segundo, CA 90245 

(310)615-0116 

http://us.wlabs.com/    

In-depth explanations of test descriptions and fees available online: http://us.wlabs.com/services/

  • Soil 

  • Water

  • Plant tissue (nutrient testing)

  • Heavy metals including lead

Waypoint Analytical, Inc.

(formerly Soil and Plant Lab)

4741 E Hunter Ave Ste A

Anaheim, CA 92807

(714) 282-8777

www.waypointanalytical.com

Test descriptions and fees available online:

Some videos: http://www.waypointanalytical.com/Videos

  • Soil 

  • Water

  • Plant tissue (nutrient testing)

  • Plant pathology (disease)

  • Nematology 

  • Fertilizer/Compost/Herbicide residuals

 

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