You want to stay away from sap wood. Conifer bark has the right physical and chemical properties for a container mix whereas heart wood and sap wood do not. I believe you'll find a more detailed explanation of the "why" on the "Container Soils - Water Movement & Retention" threads.

That said, most bags promoted as bark will contain some proportion of heart/sap wood. The "15%" may simply be their manufacturing spec--meaning "this product may contain up to 15% sap wood" You just can't tell without inspecting the product. The sap wood should be immediately evident because it looks like wood--not bark. It could be that there's actually very little sapwood and you can hand-pick it from the mix. If it's truly 15%, you'll have to decide if it's worth the effort.

Good luck!

There are 3 negatives associated with hardwood bark and products that contain significant amounts of sapwood. There is often a rather high pH spike that occurs at some point during the composting process; there is a good deal of (exothermic) heat produced by the composting process because of the speed at which sapwood/heartwood/sawdust breaks down; there is a measure of N immobilization associated with wood products that break down quickly that can be difficult for growers to deal with w/o over-fertilizing unless they are specifically aware of what's going on and reacting appropriately.

Al

Al thanks for your response. You are a wealth of knowledge. If I'm making a mix that is 3-2-1 and 15% if the bark would be sap wood would that have a negative affect on a 25 gall pot. If it will, I will continue to try and find bark fines in the heart land.
Thanks in advance
Bruce

You know, it's hard to say .... I usually look at the bark I buy & just mentally try to determine )I guess) whether or not it's more than 10% sapwood. If it is, I usually pass ..... but there's a big 'BUT' that goes along with that as a qualifier. ..... but if I didn't have several sources of bark to choose from at any given time, I wouldn't be quite as picky about the 10% guideline. If that's all you can find, go ahead and use it. It's hard to imagine that the extra 5% of sapwood is going to be your downfall. You know it's not ideal, so just keep your eyes peeled for something that might be a little better - if you don't find something, then do the best with what you have. I'd take a well aerated mix with minor imperfections over a heavier soil any day.

BTW - good luck to you ..... and thanks for the kind comment.

Al