No thoughts, just let us know how that idea goes for you.

Granite, far from being mere filler, is a great element for a gritty mix*.

It contributes well to porosity if used properly with, for me, a mix of it, Turface, and some soil. 40/40/20, roughly.

Turface is easy to find in the States and in La Belle Canada. It might be a largish distance to get, but it's available in all 50 (subject to being wrong about that, but it's in most - just use the Turface locator on their webpage).

I've not used the Napa product, but with my mix I don't need to.

*with sieved soil and possibly decomposed manure sometimes'

I finally got my hands on some chicken grit (granite) today, shipped from Amazon.com so it was quite expensive but this bag should last me awhile since I don't have that much plants.. Turface is also obtainable for me now so I will definitely try the 40/40/20 mix of these three ingredients next time around.

None of the ingredients serve a nutritional purpose. If you wanted to you could just use 1/4" gravel but you would have to water very frequently and the bulk density would be very high. You could increase the water retention by adding DE or turface (calcined clay) which would also decrease bulk density. You could decrease bulk density drastically by adding bark. It is really about figuring out what you need. For instance I use a lot of gravel in some pots because I have a very windy site and the bulk density from the grvel keeps plants from tipping over. When bulk density is unwanted like in a hanging basket I omit gravel completely and use lighter more water retentive ingredients. Some of those ingredients you mention like kitty litter can work if the quality is right (some kitty liter will be fired too low and dissolve when soaked in water overnight). Vermiculite however will compact too quickly and not be worth the money. Understanding the principles about constructing a medium with good air space, water retention, and a useful bulk density are what's important.

"Vermiculite, perlite, and also potentially cat litter could all be used in place of napa oil dry/turface."

Vermiculite is too fine and spongy. It would just clog the pores paces you're working to create. Perlite would actually be a better replacement for granite, holding a bit more water than granite, but much less than Turface/Floor Dry. Cat litter can be a decent replacement for Turface/Floor Dry, but you need to be very careful when choosing one. Most will disintegrate when wet. Better to stick with a proven product if at all possible. "Granite is just used (presumably) for filler, as it serves no other purpose nutritionally."

It doesn't serve any nutritional purpose, but it is necessary to balance the water retention. By varying the ratio of granite to Turface/Floor Dry, you can increase or decrease the water retention to match your needs. It's very important in that respect. "Bark is optional, but couldn't mulch work as well?"

Some mulches are composed of bark, but any mulch including sapwood is not appropriate. The sapwood will break down much more quickly than bark, clogging pore spaces and tying up nitrogen in the process.

Now that I've nixed all those ideas :), there are substitutions that can be made.

Turface can be replaced with Napa Floor Dry, Oil Dri (hit or miss, must be tested for durability), or Schultz Aquatic plant soil or clay soil conditioner (both are rebranded Turface products sold at a higher price).

Granite can probably be replaced with appropriately sized perlite, pumice, or lava rock. I tested these products for water retention, and while they do hold significantly more water than granite, they should still be closer to granite than Turface. Some people claim that pumice holds far more water than perlite, but in my test they were quite similar. Perhaps there are different grades of pumice? You would have to increase the ratio of these products to Turface in order to compensate for their increased water retention, but they should work fine. I use a perlite, bark, Turface mix on some Hoyas with great results. Pumice and lava rock may be difficult to find in a small enough size, so that needs to be considered.

I don't have any substitutes for bark, but it can be obtained from several different sources. Most people look for bark based mulches from landscaping/big box stores. Other sources are orchid bark and Zoo Med's ReptiBark from pet stores, but these will usually be more expensive. Bark is not an essential ingredient, so you could just eliminate it as well.

I would not add peat, topsoil, compost, or any fine component to a gritty mix, because it is unnecessary, and it eliminates the pore spaces we are working to create.

I think that's about it for my suggestions. Hope it helps.

-Chris

Definitely skip adding any kind of soil or peat moss, which will simply clog up the pore spaces and render the gritty mix useless. Kitty litter typically has chemicals added for eliminating odors from cat pee, which is what it is for. As noted, it usually isn't calcined, or fired at high temps and will mush up when wet. I agree to stick with the time tested ingredients and commonly mentioned alternatives, and not try to reinvent the wheel.

Joe