Pruning Purpurea?

[cpkid]

I have a S. Purpurea in a bog garden on my front porch that is pretty much taking over. It's in direct contact with a Leucophylla, a Rubra, and a VFT, and it's only now starting to put out it's first leaves for this year. To me, that seems a little late in the year but everything seems to be getting a late start due to the rough winter we've had. It's looking like if this purpurea expands any more it will put the health of the other plants at risk, and I would like to trim it back, but I don't know it that would severely affect the health of the purpurea. Would it? Photos of the situation:

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[Aidan]

This is what happens when you mix plants in a single container and let's put it like this... It won't do the plant any good to 'trim it back'. The best option will be to pot it up separately.

[tanukimo]

I agree. If you cut off the new growth you will only be setting it back. You should repot it like Aidan said.