ever bought a bag of potting soil, you may have been astounded
to see it labeled “soilless.” Huh? If it’s not
soil, what is it?
Most potting soils are made up largely of
peat moss, bark, and perlite. (Perlite looks like tiny white
pellets; it’s actually heat-puffed volcanic glass, included
to keep the mixture from being too dense.) Often, potting soils
are sterilized by steam to kill potentially disease-causing microorganisms.
So potting soil isn’t really soil,
because it lacks both minerals and humus. Lifeless and devoid
of minerals, potting soils “do no harm” but generally
deliver few nutrients. You’ll want to fertilize early and
often if growing plants in potting soil.
Actually, “soilless” potting
soil helps make an interesting point: You don’t really
need soil to grow plants. Hydroponic gardeners
grow plants using only nutrient-rich water. In place of soil,
inert substrates such as perlite or rock wool may be used to
provide aeration and structural support for roots.