I have several 8 year old citrus trees that do well in 50-gal plastic wine containers cut down 2/3 the way up. I worry about the long term health of the trees as they become more root-bound in maturity, and pruning citrus both often removes the next-season's fruiting canes and also stimulates just more growth. Still, I've had really good results with these potted citrus, particularly after taking Millet's advice with the low biuret urea spraying in early spring, etc. Last year, I might have averaged 50 fruit per tree (oranges, lemons, limes, mandarins).
This past weekend, I planted 13 one two old citrus trees (one year since shipping from the nursery) that were starting to get root-bound in their 5G pots. I am using air-pruning expandable root-builder containers for these trees, so it will be interesting to see how they perform compared to their older brethren in hardened, traditional containers of much greater volume. In my area, I make a point to plant these trees to get shade in the afternoon and pick-up the morning light. Full sun exposure or afternoon heat results in drying and stress in my experience. I have used the coco hulls more as a top layer mulch than as one of the main components of my planting mix. For the mix, I have a combination of path-fines bark, peet, decomposed granite or sand, forest humus, and perlite w/ some organics and micro-nutrients mixed in. The bark and peet make up over 50% of the mix with about even parts of the remaining constituents.
Here's a link to the not so pretty trees just transplanted:
http://tropicalfruitforum.com/index.php?topic=7511.msg346848#msg346848