Soil Testing and Care 

Plant Nutrients
Before discussing soil testing, a little information about plant nutrients is needed. Plants need 16 elements for normal growth. Carbon, hydrogen, oxygen (which comes from both air and water) and nitrogen (in the soil) make up 95% of plant solids. The other 12 essential elements are phosphorus, potassium, calcium, magnesium, sulphur, iron, copper, manganese, zinc, boron, chlorine, and molybdenum. With the exception of phosphorus, potassium, calcium, and magnesium, there is usually a large enough amount of these elements in the soil for plant growth. Whether they are available for plants to use depends upon a properly adjusted soil pH. 
Why should I test my soil?
Testing your soil will answer the questions “Do I need fertilizer, what kind do I need, and how much?”  A soil test will also measure the pH of your soil, and provide recommendations for fertilizers and adjusting the pH, if necessary. When gardeners apply only as much lime and fertilizer as is necessary and at the appropriate time, nutrient runoff into surface or ground water is minimized, money is saved and plant health is optimized. Soil testing can also be used to diagnose common nutrient deficiencies or toxicities for plants that are growing poorly.
Where to get a soil test kit?
Soil test kits are available at the Virginia Cooperative Extension Offices in all of our counties. Both instructions and a soil collecting box are included in the kit. Samples can be taken using an ordinary shovel, spade, or even a garden trowel, but the easiest way to take a sample is by using a soil probe. Some soil probes even have a small foot pad to step on when taking the sample. These ‘step in’ soil probes are the easiest of all to use, and may be available for loan at your extension office. Your Extension agent or Master Gardener Help Desk can assist you with interpreting the test results.