Answer: The roots of your privets should adapt to the odd shape of the container. You don't want to stuff the rootmass into a small opening so I'd suggest unpotting the privets and then massaging the roots to elongate the root mass so it will fit nicely into the pot. You can do this gently without harming the roots, but don't take too much time as you don't want to expose the roots to the drying effects of air and sunshine. Once the roots are happily situated in the new pots and you've gently firmed the soil down, water well to help settle the soil.
Enjoy your new topiaries!
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