I apologize for this delayed reply to your gardening question and hope it is still helpful to you.
You can go ahead and prune the line trees now by cutting the branches off at the trunk to form a more "treelike" structure. You may want to prune a little now and a little more a month from now as you shape them into the desired form. Don't for an anymore after August because you don't want to encourage a lot of late-season growth since these plants are not that hardy.
Thanks for the question. Best wishes for a wonderful gardening season. Please stop in again soon!
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