Updated: Jan 23, 2020
Meade County Extension Office
How much fertilizer do you really need to use on your lawn and garden? If you’re just making a guess, you could be using too much. But how can you know for sure? A simple and inexpensive soil test can tell you all you need to know to make your lawn and garden look great and to protect the environment from runoff of excess nutrients.
Soil fertility testing is a program designed to provide homeowners, landscape contractors, turfgrass managers, greenhouse managers as well as others with a soil management tool to determine fertilizer requirements of their lawn, garden, trees and shrubs. The University of Kentucky Agricultural Experiment Station and Cooperative Extension Service offers soil testing services to every Kentucky citizen. Soil testing is the most important thing you can do before applying fertilizer. Fall and spring are the best times to take samples and you should sample your lawn, landscape beds and vegetable gardens every 1 to 2 years, since your soil’s needs may change over time.
You can use the test results to determine the amount and kind of nutrients you add to your lawn and garden for best growth. A routine soil test from the University of Kentucky lab will provide you with information about the soil pH, plant available phosphorus, potassium, calcium, magnesium, zinc and cation exchange capacity of your soil. The results will include a recommendation about what amendments, if any, you may need to improve plant vigor and yield. Other special tests are available, however this routine test will address most home lawn, landscape and gardening needs.
Your Meade County extension agent can help answer your questions about taking the sample and turning it in. Generally, to obtain a useful sample, you’ll want to map out the area where you plan to grow plants or where plants already exist. It’s a good way to keep a record of your land use and results over time. Divide the area so that each soil sample represents one plant type or condition. Collect at least 10 samples for each area, mix them together and then take one composite sample that represents that area for soil testing. For example, if you have a landscape bed that contains shrubs in one area and roses in another, collect two composite samples: one composite sample from several sites under the shrubs and another composite sample from several sites under the roses.
For lawns, sample to a depth of about four inches. For gardens, ornamentals, mixed fruit trees and wildlife plots, sample to a depth of about six inches. Ideally, you should sample well in advance of any planting or spring green up to allow time for analysis, interpretation and then fertilizer and lime applications.<