A perfect gift for a gardening friend is a soil test. Commercial soil tests indicate various levels of basic nutrients in the soil. Mostly, they calibrate the fertility of the soil to guide the gardener’s use of fertilizers.
The tests, among other features, indicate the level of nitrogen, phosphorus and potassium. Some tests also indicate pH and micro-nutrients such as calcium or magnesium or boron. Gardeners often find that their soil actually has enough of the major nutrients and more bags of fertilizer do not have to be purchased.