Rodger wrote, >The lava rock that's widely sold as a garden top dressing is nothing >like real >pumice. Pumice is porous, solidified rock foam, and quite water retentive, >whereas the lava rock isn't water retentive to any great degree. > >This charming fact means that you can plan next summer's vacation >now: plan on >visiting Crater Lake in southern Oregon. The access road along Annie Creek to >the Rim Drive climbs to the caldera rim over enormous deposits of pumice, and >along US Highway 97 which runs up the east flank of the Cascades, NE >of Crater >Lake you go for miles through drift, banks, and hills of pumice thrown out by >Mt. Mazama when she lost her temper some 6000-7000 years ago. True: the mulch is what we call "scoria" and it's better as a top dressing than a soil component. However, you don't have to get your pumice from nature (if you're right near Crater Lake, it's a national park and it's illegal to take rock, anyway); you can just stop at Oregon Decorative Rock near I-5 in Portland and buy it in 60-pound sacks, nicely crushed. Jane McGary