Is it safe to plant two smoke bushes four feet apart from each other.

answer to question

Left unpruned, these can get up to 15 feet across. So the simple answer is yes, they are too close

Yes, I agree with Andrew. They are wonderful shrubs, giving interest from the moment the leaves come out in the spring in beautiful shades from crimson to lemon yellow depending on which one you have, then you get the 'smoke' and then the fabulous autumn colours - they are really great! Mine is at least 15ft across. However, I bought a new one last autumn and, speaking to the lady who sold it to me, I mentioned that I didn't have much space for a new one and she told me they respond well to being pruned and can easily be contained in a small space. In short, I'd lift one of yours and move it, but if space is a problem, then an annual prune might help.

got to agree with what has already been said, and yes they do respond well to pruning/shaping..