Don't worry about what you didn't read. Soilless Mix simply provides a
medium where nutrient delivery can happen, where roots can have purchase,
and therefore support growth. In the greenhouse environment, watering is
done with a soluble fertiliser that nets out to 20-20-20 NPK, kickstarting
the plant material to pleasing maturity early enough so you'll pay good
money to buy it. There is usually enough nutrient in the mix to carry
your purchased plants for much of the planting season, but you'll have to
supplement the soilless mix with additional NPK for best performance.

Gardening does test the wallet, by design.

Sue
Western Maine

Thanks, Sue. Much appreciated.