For your potted plants to grow a healthy root system, you must use good potting soil. Don't cut corners on the soil.When you look at the root system of a Bonnie plant, you’ll find a “soil” mix that grows healthy roots. You may be surprised that it is not real soil from the earth—it is a potting mix (also called potting soil) made from composted bark, peat moss, and other ingredients that do not include earthen soil.
Why? Consider the artificial growing environment in a pot. Potted plants are watered daily and roots need to fill the pot. Garden soil would compact under those conditions, inhibiting root growth, and it would probably introduce insects and diseases, too.
A good potting mix is one that is fluffy, holds moisture, and gives plant roots the perfect balance of air, moisture, nutrition, and anchor. Roots need air, as well as water, to grow. If the potting mix is too dense or too wet, plant roots will be stunted or even die. To avoid problems, you must use a good potting mix.
The potting mix industry grew from the need of professional growers, like us, to grow healthy plants in containers for folks like you. The first commercial mixes were developed decades ago. Over time the products improved and became available to home gardeners so that now your favorite garden center probably sells several potting mixes or potting soils (the names are interchangeable). We suggest that you buy a high-quality potting mix for best results. Buying cheap potting soil is one of those times when a bargain may not be a bargain. Poor potting soils often contain muck or sedge peat, sand, and actual dirt, and may be heavy from lots of water.
How do you recognize quality? Read the label and look for quality ingredients such as sphagnum peat moss (not sedge peat), aged bark, perlite, vermiculite, lime, and a wetting agent (helps soil stay uniformly moist). Other ingredients might be gypsum, peat humus, and compost. Optional ingredients include moisture-holding polymer and fertilizer. A few even include pesticides; avoid those for vegetables and herbs. Products labeled "bagged topsoil" and "compost" are cheaper, but reserve them for working into the ground, not for pots. In a pot, where watering happens often and plant roots need to fill the container, you need a lighter medium.
One way to test a soil is to see how it drains. When soil is placed in a pot and watered, the water should start draining out within five to ten seconds. If the soil becomes soupy or water drips out slowly, you’ve chosen the wrong soil.
You can look for products certified by The Mulch and Soil Council, a voluntary program assuring certain standards. Several of the major brands of potting soils participate in this. For details about standards and a list of certified products, visit www.mulchandsoilcouncil.org.
Don’t discount your favorite soil just because it is not certified. This program is voluntary. However, it gives inexperienced gardeners or those with doubts about their soil some basis for judging.
Obviously, we want you to use the best soil possible because good soil and good plants are key ingredients of successful gardens.