What is a soil test?
A soil test will determine the fertility and pH of your soil. This is important as a lot of the things we grow only grow well when the soil is within a favorable pH range. For example, most garden vegetables grow best at a pH between 6.0–6.5. Most home lawns grow best around that same pH. Most of our soils are naturally acidic and need the addition of lime to increase the pH.
You may have seen the consequences of growing vegetables in a soil with low pH before. Blossom end rot on tomatoes, peppers and watermelon can be caused by soils with a low pH. Home lawns are another example. Often times, when grass is grown in soil with a more acidic pH, you will notice the grass thinning out. You may notice mosses starting to grow. Disease and insects are also more prevalent on weakened turf.
A soil test also checks the fertility of the soil. Many people use a balanced fertilizer such as 13–13–13. This type of fertilizer is not always neccessary. The three numbers represent nitrogen, phosphorus and potassium. A soil test will test the amount of phosphorus and potassium found in the soil and give a recommendation based on that amount, as well as the crop being grown.
How do I take a soil test?
First, make sure you have a shovel, a clean bucket, a trowel, a soil sample box and the information sheet that comes with the soil sample box.
Next, with the shovel, take a core sample of soil from as far down as possible. Try to get a sample from at least 6 or 8 inches deep, or as deep as vegetable roots usually grow. For lawns, a soil sample about 2-3 inches deep will do (the depth of lawn roots). Put the soil in the clean bucket. Move a few feet over and take another core sample. Every square foot of soil can differ, so it’s important to take a composite sample of 15 to 20 sections of your lawn or garden to get accurate soil test results. With your trowel, mix the core samples in the bucket. It is important that you mix the soil well and keep it moist but not wet. After you have mixed the soil, fill the soil sample box with about a pint. Be sure you print your name and address on the box and include the information sheet. You can mail this directly to the soil testing lab.
How often should I take a sample? How much does it cost?
A soil sample from the Auburn University Soil Testing Laboratory costs $7, which is not that expensive when you think about the cost of plants and fertilizer. It is recommended to do a soil test every two to three years. Nutrients will leach from the soil over time and another application of lime may be needed. It generally takes several months for lime to interact with the soil and bring the pH up. This makes fall an opportune time to take a soil test on lawns, which are going dormant, or vegetable gardens, which may not be planted again until the spring.
Soil testing boxes and the paperwork can be picked up at any county Extension office.
Dani Carroll is an extension agent for the Alabama Cooperative Extension System. For more information, contact your local county Extension office or visit www.aces.edu.