First, you must determine the composition of your soil before you amend it. The best way to determine what to add to your soil is to have it analyzed by an expert. Pennsylvania State University has an Agricultural Research and Extension Center in most counties. They can recommend amendments based on the results of the test.

Slightly acidic soil around 6.5 pH, is best for most plants, though there are exceptions. Adding decaying organic matter raises the acidity of your soil, and because of this most garden soil is slightly acidic already. To raise the alkalinity (raise the pH) use finely ground limestone. To raise the acidity of an alkaline (basic) soil add flowers of sulfur. Both of these products are commonly available at large hardware stores and garden centers. The amount and rate of application of these materials depend on the texture of the soil. Be careful to only add as much corrective material recommended by a reliable soil test.

The general rule of thumb for adding material to your soil is that you can always add more but you can take it away. It is very important to raise or lower your soil’s pH level slowly, preferably over a couple of years. Try to change it too much, too quickly and the soil can swing dangerously in the opposite direction.

There are 16 elements known to be required for healthy plant growth. The main three, Carbon, Hydrogen, and Oxygen, come from the air and water. All of the rest comes from the soil. Most of the remaining 13 elements are needed in such minute quantities that they are rarely depleted from the soil.

Nitrogen (N), Phosphorus (P), and Potassium (K) are the exceptions to the rule. Plants use these elements the most and because of this, they are depleted from the soil on a regular basis. Plants use Nitrogen to make protein, control their form, and help them use carbohydrates.

Plants that are experiencing a Nitrogen deficiency are common, thin, spindly, and the older leaves tend to be yellowish-green. Phosphorous helps plants set buds and flower. Phosphorous facilitates energy storage, efficient water use, and root growth. Phosphorous deficiency in plants is characterized by bluish-green leaf colorization and stunted growth. Plants use Potassium to provide disease resistance, make carbohydrates, and regulate metabolic activity.

Generally, plants take up five to ten times more Potassium compared to Phosphorous and Nitrogen. Lacking Potassium plants generally have roots that are not well-formed and possess leaves that appear burned. All fertilizers have an “NPK” rating representing the availability of Nitrogen, Phosphorous, and Potassium (by weight) making up the bag. For example, a 100-pound bag of 10-10-10 fertilizer contains 10 lbs of N, 10 lbs of P, 10 lbs of K, with the remaining 70 lbs being filler material. Three other important nutrients of Calcium (used in cell membranes), Magnesium (a metallic component of chlorophyll), and Sulfur (helps the plant create proteins). These are usually needed in minute quantities and are plentiful in rich, loamy garden soil.