Aha, finally a question I can answer! (I'm new here but I've read just about every post on potting mix I could find.)

Head on over to the "Container" forum and read the series of posts about this very topic from a very knowledgeable poster named Al/Tapla and the many many many other people who have had success with his potting mixes. There are also other folks who use different mixes, but there's definitely concensus about the idea of creating a fast draining but well aerated mix for containers to grow successfully long term.

The key thing I've learned about potted citrus is they don't like soggy roots. Basic potting mixes have too much organic material and that not only stays wet too long, but it breaks down and collapses quickly, accelerating root rot and the poor nutrient uptake.

When I got here a couple weeks ago, the idea of "home brewing" my own potting mix sounded so revolutionary and a bit crazy, and now, I'm a convert. I do a slight variation of the mix Al recommends, because I want to grow using a bit more organic material than he uses. You might also want to read his fertilizer posts... all very helpful.

Good luck with your citrus!

Here is a link that might be useful: Al's Container Potting Mix Post

He has what looks to be a good recommended soil in the several mixes at the bottom of that linked post. I would add one serious caveat. READ THE INSTRUCTIONS on whatever source of micronutrients you buy. His amount might be fine for fritted slow-release micros, or a diluted source, but that 1/2 cup for four or five cubic feet of soil looks like it easily be toxic for soluble concentrated micronutrient sources (brands). Micros have a narrow range between deficiency and toxicity.

Personally, I prefer the pine bark a little coarser than the finest available. I like the largest pieces to be about the size of my little finger fingernail, 3/8th inch maybe, and I use more perlite and less peat, both of these to improve drainage. I have to water a bit more often probably.

Chariko-- I'm up north of you in Saipan. I want to order some citrus, but couldn't find anyone to do it-- I can't believe you found someone!! I'm checking it out, and I've got my fingers crossed they'll let me order. I'd like to e-mail you-- my contact info is on my profile page.

I have no idea if you'll be able to find this stuff or not, but I use coconut husk chips and ground coconut coir with my trees. Excellent air flow while still keeping good water retention. Lasts longer than any other organic media that I've tried under Florida conditions as well. At present I'm using 3.5 parts medium chips (1/4-1/2 inch size) to one part coir. Once mixed I treat it with magnesium sulfate (Epsom salts) and calcium nitrate to leach out any residual salt. My oldest tree has been in coconut chips for right at three years now. I'll have to repot it come spring.

If you can't find those then I'd look at pine bark chips or nuggets in the 1/2 size or thereabouts mixed at 4 parts bark to one part spagnum peat. Good air flow, good water retention. In my experience under Florida conditions it doesn't last as long as the coconut chips, but it works well enough.

If even that can't be found then I'd look at an orchid mix with a bit of additional peat mixed in. Not the best, but it has some durability and ought to keep you from getting into trouble with water logging.

.....Alan.