Despite the name, there is actually not much soil in potting soil. Instead, potting soil is a mixture of peat moss and other organic materials, water-retaining vermiculite crystals and fertilizer. Container gardeners prefer to use potting soil instead of dirt in containers because dirt contains fewer nutrients as well as microbes that can damage the roots of a potted plant. When choosing a potting soil, select one that is formulated specifically for your type of potted plant.
Look through a plant identification book and identify your plant. Many plant identification books list the nutritional needs of each plant, including the pH level of soil, the plant's water needs and the balance of nitrogen, phosphorous and potassium that plants need to survive.
Select a potting soil mix that is designed to retain the right amount of moisture for your plant. Desert plants require a sandy potting soil with fewer nutrients and better water drainage. Miracle-Gro makes a number of potting soils specifically for popular plants, such as orchid mix, and cactus palm and citrus soil.
Select a potting mix that is pH balanced for your plant's needs. Most potting mixes are pH 7.0, which is neutral. However, plants such as African violets need more acidic soil. Potting mixes formulated for African violets are pH balanced 6.0.
Pay attention to the numbers that indicate the ratio of nitrogen, phosphorous and potassium in a fertilizer (N-P-K). Foliage plants should use a potting soil higher in nitrogen such as (20-10-10) to promote healthy leaf growth. Flowering plants require phosphorous for healthy root structure and abundant blossoms (10-20-10). Potassium, such as is found in potting soils labeled (10-10-20), promotes the plants' health and disease resistance.
Consider the micronutrients that are present in various soil blends. Micronutrients include iron (Fe), magnesium (Mg), sulfur (S) and manganese (Mn). Iron helps to make plants greener, magnesium helps move nutrients through plants, sulfur helps stimulate plant growth, and manganese helps new seeds to germinate and mature.