First of all, what kind of plant is that? From the looks of the leaves, I will guess that it is some variety of Holly. If it is a Holly, then (depending on the species) you'd probably be fine to transplant it to it's eventual location in the ground. A lot of Hollies are very hardy. And most shrubs and trees are best planted in the fall, when they go into dormancy, so that they get established over the Winter and are ready to do lots of growing in the Spring.
If you don't plant it out now, then get a pot about twice as big and put it there until March.
Best of luck!
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Plantae/Magnoliophyta/Magnoliopsida/Fabales/Fabaceae/Mimosoideae/Acacia