Most soilless potting media are designed to have a minimal amount of starter
fertilizer and to be irrigated with a dilute fertilizer solution. This can
be at every irrigation, so called fertigation, or at some other interval
such as once a week. There are also controlled release fertilizers (e.g.
Osmocote) that last for 3-4 months or other intervals.
Adding topsoil to soilless potting mixes is not necessary to provide
micronutrients as there are micronutrient fertilizers (e.g. MicroMax) that
can be added and many soluble fertilizers (e.g. Peter's) often contain
micronutrients.
For house plants, I often just use sphagnum peat moss to which I've added
some ground limestone (calcium carbonate) or dolomitic limestone (calcium
magnesium carbonate) to raise the pH to about 6. The small amount of perlite
some potting media contain has little effect on the physical properties of
the medium.
David Hershey
dh321 at mailexcite.com
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