They are sterile and free from diseases, they have a fairly neutral ph (especially perlite which is neutral), and they are readily available, non-toxic, safe to use
Add vermiculite to soil for conditioning and lightening either alone or in conjunction with peat or compost. This will accelerate the growth and promote anchorage for tender young root systems.
Using vermiculite as growing medium will also enable the plant to more easily absorb the ammonium, potassium, calcium, and magnesium necessary for vigorous growth.