Answer: You will be able to prune both your plants so they're more uniform in size. I'd plant the new one now but wait until next spring to do any pruning on it. Your current one can be pruned back a few inches now and a few more inches next spring. Don't cut back too much at any one time or you'll end up with bare branches. By this time next year both arborvitaes should be the same size. Best wishes with your garden!
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