Cattleyas - How Dry is Dry?

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I think the "dry between watering" idea originated with people growing with high risk of fungal attack: high humidity/poor air circulation, either from ambient weather or growing in a greenhouse, or growing in relatively cool homes.

There's usually plenty of air circulation on a windowsill without a fan. Extra can help prevent sunburn.

I would try to give Catts a temperature drop at night. The ones you mentioned are among those that tolerate higher night temperatures pretty well. Mine are happier spring and fall, with lower night temperatures, than in summer, when my growing area is around 85 degrees F / 29C most of the time.