Hi North!

I am going to say:

Not a good substitute since you want your ingredients to be as uniform as you can get it.
Unless crushed volcano particle size is fairly uniform and/or larger than about BB size, it will not serve it's purpose in the gritty mix. 1/16 is about as low as I go on any ingredient for the gritty mix

It would be way to fine for the gritty since the bark sizes will be what you could use in the 5.1.1 mix as a substitute for peat:-)

Are you sure no one within miles from you sells anything comprable to it?

Mike

i researched the volcanic stuff yu're talking about, and it seems to be used as a potassium source. does not seem to be something you would necessarily want in your gritty mix. what ingredients are you looking for? if you can tell us what you have we can help you find what you need. personally, i made some makeshift gritty mix from mostly materials i found in my environment (like, on the ground). not ideal, but it served the purpose.

apologies from my complete lack of capitalization and poor grammar. i'm posting from my phone, and it's a complete pita. my work has a weird firewall that prevents me from logging in

Often, searching for the right ingredients in the right sizes with which to build a decent gritty medium can be difficult, but if you think of it more in terms of a treasure hunt, you can actually have a little fun with it!

You'd be surprised at the different places our ingredients can hide... I located the fir bark I needed at PetsMart, as a reptile bedding product. It's called ReptiBark, packaged by ZooMed. Other places to locate pine/fir bark fines can include orchid growers, mulch companies, garden centers, home improvement stores... and you might find other ingredients, such as granite chips, at farm oriented stores, or gravel companies.

Some ingredients can be located at hydroponic stores, stores catering to bonsai growers, or online suppliers of various materials.

Or... perhaps someone over at the Container Gardening Forum can help you locate the items you need. I've included a link to a thread that might contain pertinent information for you... I'm not entirely sure, but it's worth looking at... link below.

Here's another link to a website on bonsai which might help... copy/paste the web address into your browser...

http://www.bonsai4me.com/Basics/Basicscatlitter.htm

Good luck... and if we can help further, we'll certainly try! :-)

Here is a link that might be useful: Ingredients by State/Region...