Soil Sampling Instructions
Understanding your soil is the cornerstone of successful gardening, landscaping, and agriculture. Soil testing provides crucial insights into nutrients and mineral levels, pH balance, organic matter, and other chemical, physical, and biological soil characteristics for plant growth. However, the reliability of the soil test results depends upon the quality of the sample submitted. The soil test result is only as good as the sample collected. A sample must reflect the average soil properties across the area of interest (a field, garden, lawn, or flower bed).
Tools
- A stainless steel soil-sampling probe, an auger, or a shovel/trowel (Figure 1)
- Clean bucket
- Plastic bags or waterproof lined paper bags
- Permanent marker
Sample Collection
Use a systematic and/or random sampling pattern to collect samples (Figure 2). The number of samples you need to collect depends on the size and variability of the sampling area. In general, more samples are better as they provide a more accurate representation.
Collect a representative composite sample by combining 10 to 15 samples from the soil surface (0 inches) to a depth of 6
inches OR 8 inches (0-6” or 0-8”) for vegetable garden and flower beds; from the soil surface to 2 inches OR 3 inches. (0-
2” or 0-3”) for lawns; and from the soil surface to 8 inches (0-8”) for agricultural crops.
Submit a separate sample for areas with different crop growth, soil color, or fertilizer/amendment history. For example, a homeowner may submit one sample from a vegetable garden, one from a flower bed, and one from a front lawn. A farmer may submit a sample from each field, different crops, or from an area of low and/or high productivity.
When using a soil probe, Insert it into the soil to the proper depth (0-6” or 0-8”). Remove the soil core and place it into a clean bucket. Repeat this process at each of the predetermined subsampling points within your designated area.
If a tool such as a spade is used, dig a V-shaped hole to sample depth (6 inches OR 8 inches); then cut a thin (approximately 1 inch thick) slice of soil from one side of the hole. For the sample, save a 1-inchwide strip of soil from the center of the spade (Figure 3).
When using an auger for sampling, bore a hole to the desired sampling depth (6 inches OR 8 inches) and then withdraw it. Replace the auger tip with a core sampler, lower it down the borehole to the sampling depth. Withdraw the tube core sampler and collected the sample.
Once you have collected all the necessary subsamples from your defined area, it is time to combine them into one representative sample. This is referred to as a composite sample.
Thoroughly mix all the subsamples in a clean bucket. This ensures that any variations between sampling points are averaged, giving a more accurate representation of the soil conditions. Break up any large clumps of soil, remove and discard surface litter (crop residue, grass, wood chips, manure, roots, or rocks/gravel), and mix thoroughly until you have a homogeneous mixture.
Take one pound of the mixed soil from the bucket and place it in a clean plastic bag or waterproof lined paper bag. This is the representative composite sample to be submitted to the Lab.
Using a permanent marker, label the bag with your name, sample depth, and sample name such as FIELD1, GARDEN1, LAWN, BACK YARD, etc. Fill out the appropriate submittal form, found on this web page. For lawns, vegetable gardens, flower beds, trees, and orchards as well as reclamation sites, use the Horticulture Soil Submission Form. For agricultural crops, use the Crop Soil Submission Form. Make sure that the sample name on the bag matches the Sample ID on the submission form.
Selecting a Soil Test
The soil testing packages offered by the SWPTL are soil management tools for anyone interested in diagnosing and correcting soil fertility problems, determining the fertilizer requirements of their crops and improving soil health.
Our most popular soil test is S1. This comprehensive test is suitable for farmers and ranchers, agronomists, homeowners, landscape professionals, and environmental consultants. It provides information on all essential nutrients and minerals a crop/plant needs for optimum growth and development.
Soil Texture (S11) is also a key test to understand soil water and nutrients holding capacity and water drainage, and organic matter decomposition among other soil properties. This test determined the percentage of sand, silt and clay.
Submitting Samples
Colorado State University County Extension offices throughout the state provide sample bags, tools and technical assistance for collecting and shipping samples, and results interpretation.
Samples can be submitted in person or mailed. When mailing samples, place sample(s) and submittal form in a sturdy box or envelope. Seal the box with packing tape and mail it to the address on the submittal form. You will receive the soil testing report within 7 to 10 business days.
Dropping or Mailing Address:
Soil Water and Plant Testing Lab
Terra Building T 3-16
4780 National Western Drive
Denver, CO 80216
Payment
Payment is expected at the time of sample(s) submission. Purchase orders are accepted for city offices, landscape companies, crop and environmental consultants, schools and universities.
With the exception of existing accounts, all other sample submissions must be accompanied by a check or money order made payable to Colorado State University for the total amount due.
For information about purchase orders, invoicing or payment, contact the SWPTL at soiltestinglab@colostate.edu or by phone at (970)491-5061.