Soil Sampling Essentials

by Andrea Laine, EMGV

Our master gardener office has fielded a lot of calls lately about soil sampling. And, we are a little more than six weeks away from the end of soil sample “free” season, so a refresher on how and why to prepare a soil sample seems appropriate.

Let’s begin with the end: November 28 is the last day soil samples will be accepted in the Durham  County Extension Master Gardeners office at 721 Foster Street, Durham. The Extension office is open Monday through Friday, 8:30 a.m. to 5 p.m.

Why bother with testing soil? It is the best way to set your garden up for success. The test results will tell you exactly what nutrients need to be added to the soil to grow what it is you desire in that spot.

Who tests the soil? The folks who analyze soil samples work for the N.C. Department of Agriculture & Consumer Services (NCDACS) in Raleigh. They are agronomists – soil scientists — and can also help you understand your soil sample report; Do not hesitate to call the telephone number on the report.

Master gardeners figure prominently during “free season” because one of us transports your collected samples to the right place in Raleigh for you. If you ask me, that’s even better than being free! Homeowners who sample soil between December 1 and March 31 must deliver the sample to the NCDACS themselves and the cost per sample is $4.

What will you need for this task and where can you get it? In addition to basic gardening equipment, you will need:

  • soil box
    soil sample box

    One soil sample box for each area of your yard that you wish to test. (See photo to left.) Do not assume that all the soil in your yard is the same. And know that it is perfectly acceptable to sample the soil in a raised bed.

  • A Soil Sample Information Form. One form has room for up to six areas.

So, that’s one form and multiple boxes. Soil boxes and forms are available from the Master Gardener office  and local garden centers (usually at the cash register). The boxes and forms are free.

How to obtain a good soil sample? Follow these five steps:

  1. Choose a day when the soil is relatively dry. Digging in wet soil is rarely a good idea.
  2. Prepare by cleaning and clearing; You want to begin with a clean stainless-steel shovel and a clean plastic bucket. Then clear away grass, twigs and leaves from the soil’s surface.
  3. Dig a V-shaped hole (strive for eight inches deep for a garden, four inches deep for a lawn).  Take a one-inch slice from one side of the hole and place it in the bucket. Do this at least six to eight times. To obtain one sample, you must dig several (or more) shovelfuls of soil from different spots within each area being sampled. This will ensure accurate results.
  4. Using a clean tool, mix the soil. Remove rocks and other large pieces of organic material. From this mixture, fill the soil sample box to the red line. Close the box. (If you have difficulty closing the box, don’t despair, try again. It will close eventually. Please do not tape the box.)
  5. Complete the Soil Sample Form. Two important points here: First, for each sample, you must choose a 5-character ID and place it on the sample box and on the sample form. That’s how you will know which results belong to what samples. I generally choose geographic descriptions like “fence,” “front,” or “woods” to distinguish the location from which I took the sample. But use whatever is meaningful to you. And it never hurts to write it down in your garden journal for future reference. Secondly, choose a “planting code” for each sample. This is a multiple choice question; choices are listed on the back of the form.

    soil codes
    One of these “planting codes” must accompany every soil sample.

Bring the sample(s) to the Master Gardener office within the Durham Cooperative Extension building at 721 Foster Street in downtown Durham before Nov 28. You will receive an email when the results are ready. The email will contain an online link to your report.

If you have questions at any stage of the process, feel free to contact the master gardener office by phone (919-560-0528), or by email (

NDDA&Cs Agronomic Division, Soil Testing Section

NC Cooperative Extension Services, Durham County Master Gardener Volunteer Program, Urban Horticulture Note No. 5: Submitting Samples for Soil Testing, October 23, 2007

Further Reading
A Gardeners’ Guide to Soil Testing

Photo credits: Andrea Laine