Composted Bark

Basically rotten bark

Put bark in a big pile and allow it to rot for 4 months (when it's 150 degrees in the middle on the pile, it's done) and you've got yourself some composted bark. Composted bark is actually much heavier than peat.

If composted correctly, bark can resist disease. On the other hand, new bark and fine particles can cause problems. In addition it helps to have properly sized chunks of bark which will help to aid in porosity.

Needless to say, it's a lot easier just to buy the stuff and know that you can trust what you buy.