Orchid bark is fir bark, and high grade fir bark at that, which is actually slightly to superior to pine bark and longer lasting. As Graydon says, the trick is to get the right size. Most bark for landscape or orchid use is too large, but not always. In most of the West and all of California you should be able to locate 'small', 'mini', 'micro', or 'seedling' orchid or fir bark. If the chunks are 1/4 to 1/2 inch, it is fine to use for bonsai. I go through dozens of 2 cu ft bags of it a year. "Greenhouse" is an excellent brand on the West Coast, but I am not sure you can find that far south. I use "Greenhouse Mini Mulch", and it is a superior product. They also make "seedling" orchid bark that costs about 3 times as much, but it is to die for. Hard to locate though.
Shipping is going to kill you on bark, try to find it locally. You are not very far from the mega wholesale nursery Monrovia, so there much be decent bark down there somewhere.
Brent
EvergreenGardenworks.com
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