Typically, soilless mixes are composed of peat moss mixed with perlite and/or vermiculite. They tend to be very lightweight and often need to be watered more frequently. After soilless mixes dry, they can be difficult to re-moisten. You can purchase premixed bags of soilless mixes at most garden centers or nurseries, or you can mix your own. Soilless mixes contain many of the same ingredients as potting soil, but they are two to three times lighter because they don’t contain heavy soil.
Common ingredients include: peat moss and/or ground bark to hold water and nutrients; vermiculite for water retention; and perlite to loosen the mix and allow for air movement. You can add up to 10 percent of the volume as clean, coarse sand to add weight for top-heavy plants. For more information on container gardening and soilless mixes, please see the Colorado State University Cooperative Extension Fact Sheet #7.238 "Container Gardening" at http://www.ext.colostate.edu/pubs/garden/07238.html.
