Accurate Soil Test Sampling
Last updated: 8 March 2024
The purpose of a soil test is to get recommendations on the correct amount of fertilizer, lime, or other amendments to apply to your lawn or landscape beds. Proper sampling is the key to getting accurate soil test results. Improper sampling will return misleading results.
Fertilizer becomes a pollutant when it is misapplied or over-applied and nutrients run into the surface water or leach into the groundwater. Proper application rates and timing is important as well as basing fertilizing on a reliable soil test. Protect our water sources! Fertilize responsibly.
A soil test will help you:
- Apply the correct amount of fertilizer for the plants you are growing.
- Prevent surface and groundwater from being contaminated by excess fertilizers.
- Confirm the soil pH is appropriate for the type of plants you are growing.
The goal of sampling is to gather a composite sample that is representative of your lawn or landscape beds. For lawns, this is accomplished by taking at least 10 sub-samples from the test area and mixing them to form a composite sample. Take a minimum of five samples in landscape beds. The soil submitted to the lab is taken from composite samples.
Follow the specific instructions that come with your testing kit. The guidelines in this article will help ensure you’re getting accurate results and good recommendations.
Take a separate soil test for each distinct area of your yard. For example, a separate soil test should be taken for the front yard, back yard, and landscape beds. The reason for this is soil composition often varies from one spot to another. Additionally, nutrient recommendations are customized for vegetation type and landscape beds are fertilized differently than a vegetable garden or a lawn. Dividing your lot into testing areas is more important for large lots than for small ones. For small lots, it’s okay to take just one test for the lawn areas and one for the landscape beds.
A soil test is also a valuable diagnostic tool for lawns that are growing poorly. Trouble spots should be tested separately from the rest of the yard.
Soil Testing Tools
The tools needed include:
- Soil testing kit
- Clean plastic bucket or container
- Stainless steel soil sampling probe or hand trowel
- Gloves
A soil test kit generally costs $20 to $30 depending on the service that you use. I recommend the Soil Testing Kit from Yard Mastery or the MySoil Kits available on Amazon. These are professional DIY kits that combine accurate soil testing technologies with an easy-to-use process. Reports are available online within 6-8 days.
Order one testing kit for each unique area of your yard.
The MySoil and Yard Mastery soil testing kits contain everything you need to submit a soil sample.
- Instructions for registering your kit online and collecting a sample
- Scoop and jar containing DI water and nutrient adsorbing capsule
- Addressed and postage-paid envelope
Results are available online in 6-8 business days.
It’s very important to use clean, tools that are not rusted or galvanized to avoid contaminating your samples, stainless steel digging or probing tools are recommended.
Use a clean plastic bucket or container to collect and mix sub-samples into a composite sample. I like the quart-sized containers found at paint or home improvement stores.
Use a stainless steel probe, garden trowel, or spade to collect sub-samples. I prefer using a soil probe because this tool makes it easy to collect 1/2″ diameter samples to the proper soil depth (lawns – 4 inches excluding thatch; trees and shrubs – 8 inches).
I use an 8-inch MySoil probe that takes 1/2″ diameter samples. This tool works great for me because it allows me to quickly take 10-15 good-quality sub-samples at the proper depth.
Sampling Process
The composite sample needs to be representative of the soil in which plants are growing. Therefore, soils are sampled at different depths for lawns than for trees and shrubs. The sampling depth for lawns is 4 inches and the depth for trees and shrubs is 8 inches.
Take a minimum of 10 sub-samples for a lawn area and at least 5 for a landscape bed. Additional samples can be taken for larger areas.
Walk the lawn area in a zig-zag pattern taking random samples. Sample from the soil surface to a depth of 4 inches excluding thatch. For example, if there is one inch of thatch go five inches deep.
Sample locations for trees and shrubs should be from the trunk to the drip line. In a landscape bed, remove mulch/organic litter and sample 8 inches deep from the soil surface.
Avoid sampling areas that are different from the rest of the lawn, for example low, wet areas. Do not sample fence lines, borders, ditches, next to pavement, or pet urine spots. The soil in these areas will not be typical of the rest of the yard.
Place all the samples in the plastic container and mix thoroughly to make a composite sample. Remove all rocks, debris, and plant material.
Do not sample or mail wet soil. Soil conditions should be moist not wet when you sample. Composite samples should be air-dried overnight before packaging to mail to the lab.
Timing
In general, you should test your soil every three years to adjust your regular fertilizer program, as a tool to diagnose a problem, or prior to renovating or establishing a new lawn by seeding, sodding, or sprigging.
You can take a soil test any time of year. However, the best time is in early fall or early spring before lawn treatments are applied. Wait 6 to 8 weeks after fertilizing to sample your soil.
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Need help interpreting your soil test results?
If you would like help interpreting the soil test results and recommendations, please head over to the Ask a Question Page and fill out the form.
Some of the links in this article are affiliate links. This means if you click on the link and purchase the item, I will receive an affiliate commission at no extra cost to you. All opinions remain my own. PLEASE READ MY DISCLOSURE FOR MORE INFORMATION.
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