| Lots of questions here, first off about dividing: You do not need to divide for the health of the plant. Cattleyas can just get bigger and bigger and bigger. I've seen them at shows in pots 2-3 feet in diameter. So The question then becomes: do you want one big plant with lots of flowers or do you want 2 or 3 small plants each with only a couple of flowers? That's an easy choice for me. I always want a big plant with lots of flowers. There seems to be a point, a certain size, which I call "critical mass," and once the orchid reaches this size it seems a lot more vigorous and it blooms better. I like to allow an orchid to reach that critical mass.
I used to think that Cattleyas could go a few years without repotting but I dont' believe that any more. I agree with exapseratus about cattleya roots being some what susceptable to rot when left in mix that is breaking down. When using bark based mixes, I repotted every other year. I chose pots that allowed for about 2 years worth of growth. In other words don't over pot them. Before I moved to Australia and got really busy, I considered repotting my cattleyas every year.
When repotting I'd give it a good heavy watering and a bit of a soak which will loosen the mix and make the roots more pliable and less likely to snap off during the repot.
I am currently running a bit of an experiment with 2 of my cattleyas, they're both minicats. They're potted in pea gravel which of course doesn't rot like bark. So far they are both almost 2 years without repotting, both growing and blooming well.
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