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Happy New Year from tropical Norfolk (not!). Back in that wonderful,sultry,summer, i stuck a orange pip in a pot, & we now have a 5"tall plant growing quite happily on the computer desk. Does anyone have any tips as to the future growth, as it would be a shame to see it falter. P.S. we have a greenhouse (unheated), where i presume we would transfer it to in the warmer months. But what about soil-type, feeding,etc.? Any tips? (please)

I grew a clementine orange from a pip a few years back as I figured satsuma trees would be smaller than a proper orange tree.
I planted it in the border of my unheated greenhouse and it grew to the roof (about 8 feet) but it didn't seem to mind me severely pruning it.
It did make a nice shaped bush with a thick covering of leaves and branches all the way up from ground level. I seem to think it took about 8 years before it flowered and in the second fruiting year it was covered in oranges. The fruit takes about a year to ripen with the flowers mainly in the winter but also off & on all year. I can't say that the fruit was better than the bought ones as they were very sour, but made very nice marmalade out of them ... very satisfying.
After that I decided that it's space was more valuable than it's fruit and it had to go.

One other point, while waiting for it to fruit we used the leaves in the same way as a herb, 2 or 3 in a casserole gave a very nice citrus taste.
Another point I just thought of is mine was very spiny with thorns about 2 inches long, makes orange picking more interesting than picking gooseberries