There are really only 5 important substrate properties.

  1. total pore space,
  2. water holding capacity,
  3. air space,
  4. bulk density and
  5. particle size distribution

Without these proper physical properties nutrients in the compost will not be effective.

We all know a good substrate must drain well but not get too dry nor retain too much water. It should be always moist yet not hold too much water. The ideal potting mix should be able to be watered every day so as to bring water, nutrients and air to the plant roots. The water applied every day from the top of the pot drives old air containing carbon dioxide out from the bottom and suck fresh air in from the top. It can do all this via the above stated physical properties.

I grew up in Florida. These were my formative years. Somehow I grew an affinity for plants, flowers in particular during this time. So when I came across this very well put together .pdf file from the University of Florida, it caught my eye. Check it out. It is all about substrate particle size properties.