Well thats kind of a loaded question. Quick and easy answer you will get from most here is

1.Al's gritty mix, very well draining long lasting, does not break down or compact. Root work and repots are a breeze.Turface and granite are re-useable, can be heavy and hard to find material some need to water daily if not twice daily.

2. Al's 5.1.1, mix of pine bark, peat and perilite, good drainage, easy to find materials, light weight. Better than almost all of the shelf mixes but does need re-potting sooner than the gritty.
3. straight miracle grow or the like. cheap easy to find/use just fine for an annual situation. drainage can be poor, compaction is almost guaranteed. can be improved with perlite, turface screened pine bark etc.

My go to now is
Fafard 52 and coarse perlite in a 5 to 1 ratio. for me it drains good but also holds enough water to get through our 105 degree summer days.

head on over to the container forum for some great info.

Mike

I've had great results w/ a product made by Nature's Way. It's specific purpose is for container citrus...

"CITRUS MIX (containers) - This mix was formulated to solve the root rot problems for citrus grown in containers. It contains a mix of composted mulches, compost, topsoil, expanded shale for extra aeration, greensand to meet the higher fertility needs of citrus, granite sand, coarse torpedo sand, MicrolifeTM organic fertilizer, and Ag-Lime for the extra calcium that citrus need."

We have a Meyer lemon and 2 RoTX orange trees in ~20 gallon terracottas. The Meyer is grafted onto flying dragon, a dwarf root stock, and I still need to trim the spiraling roots every 2 years to avoid cutting back too much at once. They like H2O twice a day in the summer. I set the timer to stop once water is visibly draining from underneath. Your soil will likely need trace minerals and epsom salt amendment within 2 years. Good luck w/ them!

This post was edited by sun-junkie on Wed, Mar 13, 13 at 18:48