I live in Florida and have very sandy soil. I need good drainage, especially in the summer rainy season. I fill the holes for all my plants in the ground with the gritty mix.

What is the formula for the mix?

Search: "Gritty Mix"

I use turface, bark and grit in a 1-1-1 mix. Sometimes I use granite grit and sometimes I use perlite. I have also been known to fill the hole with perlite and backfill with the sandy soil I dug out of the hole. I have a lot of pea gravel mixed in some areas, too. The pea gravel is used in place of mulch, so mixing it in has been incidental, not intentional.

I have mounded raised beds, so some areas need the mix tweaked more than others. Plants at the top of the mounds get the turface while plants at the bottom don't need anything to retain moisture (just the opposite, really).

I hope that doesn't confuse you further!