I know this post is old, but was looking up what all the white/bluish powderey stuff is in my bark. I bought a home couple years back and the previous owner put wood chips in the entire front yard; and she had it layed way too thick.
Bark should never be layered more than a few inches. There were areas that were 12+ inches deep. I don't even like any bark because it attracts wood roaches over here. At a previous home that I owned, I had added some bark to a planter boarder, and one evening whilel sitting outside, I saw dozens of wood roaches running out of the bark; creeped me out. I looked up wood roaches and sure enough they love nesting in bark! I got rid of the bark that weekend and it got rid of the roach issue; they stayed back to wherever they came from prior to adding the bark. When I moved into my current house few years back I started replanting the front yard almost the first week I moved in! I removed most of the bark that was within 15 feet of the house; the front yard is deep. The stuff that's left is towards the street, and it's very thick in some areas; the previous owner piled it on so high that not much will grow well in it. Most plants need dirt unless you are planting bulbs! I've gotten rid of buckets of it. I put it in the "green" recycle can. There are a few areas that are still so deep in bark, and it's decaying and it has a lot of bluish-white power. So I'm not a fan of bark at all anymore! Instead of adding piles of mulch to keep plants cool, I plant very drought tolerant plants that thrive in heat. I live in Sacramento, CA. It gets pretty hot Central Valley, CA. There's a lot of nice looking evergreen perrenials that thrive in heat; need little water and flower from spring thru late fall.
