Soil Testing and Amending

Fall is a good time to test landscape and garden soils. It’s a great time to incorporate organic matter to improve soil structure; and if attempting to lower soil pH, fall is the time to incorporate sulfur as it takes time to have an effect.

Gardeners will tell me their plants are not doing well and they need a soil test to tell them what’s wrong. There are many reasons plants do not grow well and a soil test may or may not provide an answer. However, a soil test is good to base soil management on and this in turn can improve plant growth, making them less susceptible to injury when stressed by weather or pests. 

Basic soil tests are inexpensive, about $15 to $20, and sampling is easy. A basic soil test measures pH, organic matter content, cation exchange capacity (CEC) and levels of nutrients like nitrogen, phosphorus and potassium. There are a number of soil labs that conduct tests. For a list, contact your local Extension office or search online for soil labs in Nebraska.

Prior to sampling and mailing in, go to the lab’s website for sampling information, prices, and any information forms that need to be submitted. Once at the website, if a search is done for lawn or garden sampling, this should lead you to needed information. Most labs also have an 800 number to call.

For a sample, collect 10 to 15 six-inch deep cores throughout the area to mix together in a plastic, not metal, bucket. Remove any plant material or thatch from the cores before mixing. One sample from a yard may be sufficient. Separate samples from different use areas, such as a lawn or a garden, might be helpful. If there is a problem area, sampling from only that location may be needed. Most soil labs require a sample size of one to two cups. 

After results are received, feel free to call your local Extension office for information on understanding the results or incorporating recommended amendments. In Nebraska, that information can be found at .

One amendment frequently needed is organic matter. A content of 5 percent or higher is recommended and it is not unusual for soil tests to show only 1 to 2 percent. Organic matter breaks down over time and the addition of this amendment is needed on an annual or biennial basis.

Tilling in plant debris or manure at seasons end is one way to increase organic matter. One of the best amendments for this is compost which is fully decomposed organic matter. The benefits of compost for soil and plant growth are numerous no matter if soil texture is sand, silt or clay. 

When using compost, the rule of thumb is to spread about two to three inches for each six-inch depth of soil being amended; then spade or till it in to that depth. Compost can be purchased commercially or made at home using your own plant debris of grass clippings, tree leaves and more.

One amendment gardener’s ask about is the addition of sulfur to lower soil pH or make it more acid. This question arises when people have issues with iron chlorosis or leaf yellowing in plants, or because they want to grow blueberries.

While sulfur will lower soil pH, it requires pounds of sulfur tilled into soil and takes one year to have an effect. Then, because our clay soils have a high buffering capacity or the ability to revert to the original pH after amending with sulfur, this amendment will need to be repeated to maintain a lower pH.

It is often easier to select plants adapted to the pH of your soil. If you wish to attempt to amend pH, a soil test is a must to determine how many pounds of sulfur are needed. Continue to soil test annually or biennially, to determine when another sulfur application is required.

 By: Kelly Feehan, Extension Educator