In article , "pelirojaroja"
wrote:

Some things to consider:

1. Heat trapping (lava rocks gets hotter than bark mulch or other
organic) -- might make roots too hot
2. No soil amending abilities

As for #2, we have been using shredded mulch on our beds, and now have
really nice black soil there. It has improved over the native clay
wonderfully over about 5 years. When you go with rocks, this composting
process doesn't happen.

On the plus side, I do think the rocks look nice, and you don't have to put
on new mulch every year, as we do. But, we opted to apply the shredded
mulch yearly for the benefits to the soil.

Hope this helps!

-- pelirojaroja

Some while ago I read the results of a study on soil ammendment from the
top-down without churning or plowing. Top coatings of composted manures or
mulching materials that break down in a single year, it turns out, don't
just enrich the surface, but the nutrients do seep down, & in concert with
root & worm action, soils are sustained at the highest quality to a good
depth, even though never churned or plowed. Even in areas where trees
naturally mulch the ground with autumn leaves, continuous improvement of
soils occurs. Nature is just so fabulous, it so very often takes care of
itself if we humans don't add some interfering ingredient. If gardeners
despose of fallen leaves or lawn clippings, or cover the ground with
barriers or undecaying mulches, we slowly destroy the soils in ways that
cannot be fixed up by tossing peletted fertilizer around the place.

-paghat the ratgirl

--
"Of what are you afraid, my child?" inquired the kindly teacher.
"Oh, sir! The flowers, they are wild," replied the timid creature.
-from Peter Newell's "Wild Flowers"
See the Garden of Paghat the Ratgirl: http://www.paghat.com/