Well,
simply: Even if you're not in the place, were the winters permit all year outside grow of Citrus varieties... one can do the planting into free ground.
I know some guys in the netherlands and in Germany, who grow their trees into containers for water plants. Those boxes remember me to black plastic baskets, with two or four handles at top and sides, just to carry this basket around....
So here the plant comes in, usually they use a large basket.
In spring, after the last freeze periodes they dig out holes in their garden and set in the plant with their basket, fill with soil and cover with bark shreddered cover materials.
In fall, with a sharp spade they cut away all roots, which have get out of the openings of the basket into the free soil, and dig out the basket, and get the trees back in to conservatory for the winter time.
And, in my opinion, that's a very good way to do....
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Eerh, hmm, uuuh, oooh, just guessing