I've been thinking of lava rock as being equivalent to granite grit. Upon further reflection, this isn't exactly true. Granite grit is relatively smooth compared to lava rock. A piece of bark, coming in contact with a piece of granite grit, could have have an extended contact surface that is relatively tight. The contact surface may have micro spaces about 1/100 to 1/10 of a millimeter, or about 10 to 100 times the size of a bacterium, or just at the size limit of human vision. Lava rock is rougher. An extended contact surface with a piece of bark could have mini spaces in a size range of 1/10 to 1 millimeter; ie., barely above (to fully within) the limit of human vision. Turface is about as smooth as granite; so micropores in an extended contact zone between bark would be about the same size as with granite. But since granite grit sometimes has angular ridges while turface is globular, any extended contact zones between bark and turface could be larger than extended contact zones between bark and granite. An extended contact zone could mean that the internal water reservoir of a turface granule (at the pseudo-dry but glossy stage) would flow into the bark (and vice versa). While I don't believe that lava rock has an internal water reservoir per se, an extended contact zone above a tide pool (a pit on the upper surface of a lava rock) would as a mini reservoir, while an extended contact zone below a pit (on the underside of a lava rock) could act as an oxygen reservoir. ------- disclaimer -------- I have observed none of this under a microscope, nor read any soil text relating to this. I am just using logic based on my memory of my naked eye observations of turface, lava rock, chicken grit and bark. ------ punch line ------- If my logic is correct, how does all of this effect drainage, the medium and long term storage of water and oxygen after drainage, and the wicking of water and oxygen reservoirs to roots in the medium to long time frames? I have no real idea, but it is fun to think about. I speculate that the mini (1/10 to 1 millimeter) water and oxygen reservoirs in the contact zone between bark and lava rock wins in the short to medium term (about 1 day after drainage). I speculate that the micro (1/100 to 1/10 millimeter) reservoirs in the contact zone between bark and turface wins in the long term (a few days after drainage). In the system bark and granite grit, grit is just a spacer that creates macro pores (about 1-2 mm) of oxygen, not having any real function as a water reservoir.

I'm personally not a big fan of lava rock in most situations - it kind of looks out of place. Other types of rock tend to look more natural. I'm not an expert, but based on my DIY knowledge mulch is no worse than rock against your foundation, as water actually seeps through rock faster than mulch. The problems arise when you have plants or grass that require watering too close to foundation. The most important thing to ensure is that the ground UNDER the rocks or mulch is compacted & sloped away from the house to keep water from pooling against foundation. Any homebuilder or civil engineer should be able to tell you recommended slope for your area/soils, but genrally +/- 1 foot of slope in first 10 feet away from house is sufficient.

My grandmother used lava rock to "mulch" her beds, and my mother used the extra on one front bed. None of us would ever use it again, for very different reasons. My grandmother hates moving it around every time she wants to take out a shrub, weed, plant annuals, etc. It literally hurts your hand to scrape against it--like a pumice stone. My mother hates the color now, and has worked on removing what she has (stealthily adding it to Gma's yard, where it won't be noticed among the rest). She's replacing it with something more natural looking. I won't use it for all of the above reasons, but also because it doesn't break down and add any nutrients to the soil. I want my mulch to do double-duty! As far as wood mulch recommendations go, I don't remember my pine nuggets fading very quickly, but I admit I haven't used wood mulch in a while. I normally just use groundcovers and compost in place of wood chips anymore... sorry. :( Hope that helps a bit...

Biker: it's good to hear you use pumice for it's ease of use. Chances are real high that I would sift it out of the bag prior to use As some areas tend to be a little dusty from time to time in the substrate storage area. I think I should consider rinsing Don't get me wrong though I trust your word biker habits formed from cultivating disciplines are the most difficult habits to break. As I see a head shaking as I type why sift something that doesn't need sifting. In the past you where using grow stones and had some problems with certain species in your collection. Asking. A while ago on one thread or another I mentioned you wont over water with pumice. I may have used words to the effect that it will be difficult for ( even you) to over water. In comparison to grow stones is watering just okay ? easier ? more testing for you to determine ?