Correct, Harry, pine and fir bark (and certain other conifer barks) is considerably more stable than wood-chips and sawdust. It is high in lignin and suberin, which resist breakdown. In a container environment, one can easily add enough Nitrogen to off-set any minor effect of Nitrogen immobilization.

Josh

Would any bark fines work for a 5:1:1 mix or does it need to be pine bark fines? Would bark mulch (as opposed to "fines") be suitable for a container mix? Do the bark fines need to be composted fines?

thanks,

Harry

As I mentioned, it is the exterior *bark* of specific conifers that is to be used, due to its high lignin and suberin content. Pine, fir, spruce, and hemlock are the best.

Mulch will have much more sapwood included, and that will certainly break down faster and lead to potential issues with compaction, heat spikes, and Nitrogen immobilization.

The bark fines do not need to be composted.

Josh