First, to keep the tree from getting larger, you need to learn how to slow it down through a combination of culture and pruning, pruning both above and below soil line. It's not at all uncommon in bonsai to take a tree, 15 ft or larger and reduce it to 6 inches & start a complete makeover of the tree, so once you get the tree repotted & growing with something close to its potential genetic vigor, many pruning possibilities will present themselves, especially after an o/a hard pruning, which will force new branching all over the tree.

A complete repot and root-pruning should be done this spring. The repot should include removing all the soil from roots and the removal of about 1/3 of the largest roots. Large roots serve no function in containers and only take up valuable space that might be occupied by more valuable, finer rootage. You cannot sustain a trees vigor indefinitely by potting up. I can explain what happens to rootage of "potted-up" plants over long term if you wish.

In containers, citrus likes a spare soil that drains well and is well aerated. An excellent soil, one I use a variation of for all my woody plants is: equal parts by volume of pine bark, Turface, and grower grit.

Good luck,

Al

Tapla,

Thank for the excellent advice. when you mention pine bark, do you crush, sift etc. the pine bark to get it to a smaller size?

Is there a substitute for Turface? All the nurseries that I have called around here look at me as if I am speaking Greek when I ask about Turface.

Also, what is "grower grit." Could I subsitute pool filter sand for that?

Many thanks for your patience.

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This is the soil I would grow Citrus in. You could substitute Haydite or pumice (lava rock) in appropriate sizes for the Turface. Grower grit is crushed granite. It is inexpensive and available at feed stores that sell chicken or turkey feeds. It is the white part of the soil, while the tan part is the Turface.{{gwi:4343}}
Here, you can see the components separately. Disregard the soil at the top. It is the soilless blend that is in my raised beds &, though it looks pretty, it would hold too much water for container growing.
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In this pic, you see partially composted pine fines (right from the bag) at the top, and uncomposted bark at left. The other two components are fir bark and perlite. You can use either type of pine bark & it will work well, but the uncomposted bark will require more frequent watering and the use of a little more N.

To find out about Turface, follow the link below. At the bottom of the page, you'll find the 800 # for customer service. Call & ask for distributors in your area. If, when you call distributors, they will not sell direct, ask them who buys from them (in your area). Turface is worth looking for if you're serious about learning to build your own soils.

Al

Here is a link that might be useful: C'mon! I'll show you some neat stuff.

Al has given good advice. My husband has a 35 year old minature orange tree he has grown since he was a kid. Someone brought him back one of these from Florida. It kept getting bigger as he repotted it into larger and larger containers. But now he does what was suggested -- by triming the roots and replacing some of the soil and keeping it in the same pot. It has stayed the same size for the last 12 years and is only about 2.5 feet tall. It produces nice white flowers and right now has several mini oranges on it. We have seen 4 and 5 foot versions of this plant at the New England Flower Show so I know he must be doing something right keeping it small.

Good luck!