If the medium is bad it is better to repot and risk setting the plant back a year or two than to lose it to rot. But if it is possible to wait for new root growth, that's certainly better. Blooming doesn't have anything to do with it... if new roots are starting, that's the time to do it, the flowers probably won't even notice. (Some orchids root and bloom at the same time) However, not repotting that Den. nobile hybrid was the right thing to do. It will start putting out new growth in the run-up to spring, and that will be the ideal time. (Can spring be far away??

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