Good question. I'm about to go to a reptile convention, where they often sell it. I've always wondered. Following!

Better drainage water retention. Check out the container garden forum, and look for water movement in container soils by al [tapla]. He describes both a gritty mix (which I use with minor modification - chicken grit, turface or floor dry, and the pine bark (or reptibark)) and a 511 mix. I like the 511 for tomatoes and peppers in 5 gallon buckets.

When you use a gritty mix, it drains really fast. The reptibark is the only organic in the mix and provides some nutrients as it degrades. Otherwise, fertilize with half strength soluble fertilizer (foliage pro or the like) every watering during the growing season to provide your plants the nutes they need.

find a meal of information in these threads

Ann Le - I have found that I have to leave out the bark from my substrates. In our heat and humidity - especially during the rainy summers - it breaks down in about 18 months and I have a compost and grit retaining water. Then I have the very real danger of rot.

I have decided to forego the bark and make a mix of Turface, granite grit and perlite. I usually make it 1-1-1, but some of my mixes for more sensitive plants have less Turface making the mix for like 1-2-2.

This is my experience with my growing conditions. I think everyone needs to tweak the basic recipe for gritty mix to fit their own conditions. NOLA is hot and humid, too, yes?