Getting your best crop, whether vegetable, fruit, ornamental or lawn, often requires adding lime or fertilizer to your soil. But you need to know how much. If you are starting a new garden, it’s a good idea to have the soil tested. If your plants don’t seem to be doing as well as you think they should, do a soil test. Experts recommend testing your garden soil every 5 or 10 years just to be sure the soil pH and nutrients are still in proper balance.
You can buy a commercial soil test kit, but the one you get from your local Extension Service (every state has one) is more comprehensive, more accurate and usually less expensive
For $5-$10 you get a kit that includes a bag for your soil sample, a mailing label and box to mail the sample to the lab, and instructions.
First, select several areas for sampling within the plot to be soil tested. The samples should be representative of the entire plot. If some parts seem to be very different from others, do separate soil tests. Use a spade or shovel to dig a hole 6 inches deep for vegetable, fruit and ornamental garden beds, or just 3 inches deep for lawns.
Scoop a couple tablespoons of soil from the bottom of each test pit and combine all the samples. If the soil is wet, allow it to dry, then mix it up thoroughly before putting the required amount in the sample bag.
Label the sample bag, fill out the paperwork that came with the test kit, and send it off to the lab in the mailing box provided. You will be asked what the intended crop is (vegetables, fruit trees, blueberries/camellias, or lawn).
When the results of your test come back take a few minutes to understand the data and recommendations
The first thing you will notice is the result of the soil pH. For most crops, the target soil pH is in the range of 6.0 to 7.0. If the pH of your soil is significantly lower than the target (i.e., acidic), the lab will recommend adding lime, and will suggest an application rate in pounds per 100 square feet (lbs/100 ft2) or pounds per acre (lbs/acre).
If the pH is much higher than the target (i.e., alkaline), the lab may suggest adding calcium sulfate (gypsum), aluminum sulfate, or powdered sulfur (flowers of sulfur). Adding compost or well rotted manure also lowers the pH. Many plants, especially garden vegetables, have difficulty absorbing micronutrients when the soil pH is above 7.0. In addition to (or instead of) trying to lower the soil pH with sulfur compounds (which can take months), you should use a fertilizer that includes the micronutrients, or apply a commercial micronutrient mixture.
The test results will indicate the amounts of phosphorus (P) and potassium (K), and in some cases, the amounts of Magnesium (Mg) and calcium (C) in your soil sample
Results will indicate if measured values are low, medium, high or excessive, and the report will recommend fertilizer requirements for optimum production of your particular crop.
Your soil test report will recommend how many lbs/100 ft2 (or lbs/acre) of specific fertilizer materials (such as ordinary phosphate, superphosphate or muriate of potash) you should apply to your plot. It is, of course, more convenient to use a complete fertilizer (such as a 6-8-8 or 10-10-10, etc.), and the report will recommend how much to use.
If phosphorus or potassium is excessively high, the report may recommend using a fertilizer with lower portions of that nutrient, such as a 12-0-8 or a 12-6-0.
Most soil testing labs do not test for nitrogen (N), since they expect that (N) will be part of a regular fertilizing program at around 0.2 lbs/100 ft2.