Originally Posted by rockm

"Keep the bark percentage low, because it can take nitrogen away from the roots when it starts to decompose."

A myth. The decomposition of the bark isn't enough to starve roots of nitrogen, especially if you're using water-based fertlizers regularly. I think Brent pointed that out a while ago if memory serves. The problem is more to do with the structure of bark. It will break down within four or five years as it decomposes. If you use too much in your mix, the soil breaks down and loses drainage over time, where a completely "soil less" mix retains its structure far longer.