Migrant13 and Papheteer
I think the reason the leaves are in pretty good shape is that the temps don't often drop below 60, I have pretty good air circulation, the green house is a little on the dry side (30 - 60% RH) and I try to water directly into the medium which helps the leaves stay dry. Consequently, I rarely get fungal or bacterial infections. I use orchiata only on the larger plants and water frequently with dilute 1:1:1 MSU/magnesium nitrate/calcium nitrate. They also get a lot of light, as much as 4K footcandles in the winter.
Most of these are grown from flask or small seedlings, so they are well adapted to my environment by the time they are mature. Also, my growing area is an extension of my home's living space and I try to keep things as clean as possible.
Mike