Hi Jeff, I can't really answer the root ball question, but if I had to guess it will probably be okay, I know its better than planting it below the soil line. You can maybe post it on the container forum and maybe Al and others might be able to tell you for sure.

I can answer your other question about the larger pine nuggets. I have my Glenn Mango potted in Al's mix also. The time I potted it, I also could NOT find the Fine Bark Fines(I have finally found it since then,few months ago)At the time, all I could find was the mini pine bark nuggets, they were quite a bit larger than the pictures that he posted. I picked out the smallest out of the bag. Most were larger than I wanted to use. Since that is all I could find and my pot was a 20" I went ahead and used it. The only thing for me that was an issue was I had to water it often. But what is great right now, its our rainy season here in FL and we get rain sometimes everyday or 3-4 days a week. Since the larger bark makes it drain so much faster, I don't have to worry about it being in too wet of a mix too long. The downside is when we don't get rain I have to water every other day or everyday if it is over 90 degrees.

Here is the pic of my mango tree, I planted it in Al's mix in Nov '06.
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It is wise to plant a citrus tree with the topmost roots visible above the soil line. This is how nearly all Florida commercial trees are planted. Doing so makes the tree less susceptible to phytophthora foot rot.