I use pumice, 0.1 to 0.25 inches. Which is pretty much the way it comes in the bag. Various other things should work fine if pumice is not available to you locally, like perlite or lava rock or grit. When in doubt (if product is not horticultural grade) wash it with a generous amount of water. If your product has a lot of fine particles in it, you can use window screen to remove the small stuff.
Stick around and you will be seeing more of the polygona hybrids, they've been installed in a row and have already proven their merit in a squirrel-rich environment. The squirrels take one bite and decide it's not for them.
