Too Much Humidity?

[Joseia]

I've been reading some orchid culture sheets and have a question about humidity. If a culture sheet says a certain cattleya species likes a relative humidity of 50-60%, but I am giving the same orchid 70-75% in my terrarium, is that a problem? My terrariums keep an average humidity of around 75%, temps range from 83 during the day down to 69 at night, and fans provide very good air movement - no mold or fungus spotted yet after 4 months. But if I have a plant in there that does not require so much humidity, will that slow it's growth? Accelerate growth, or have no effect? I am currently growing mostly cattleya alliance orchids, with some dendrobiums and a couple of vanda alliance plants as well.

I put these plants into terrariums because it is difficult to keep humidity above 35% in our home during the winter, even with humidifiers running. Are the orchids that need 50-60% RH better off in 35% RH on the shelf, or 75% in a terrarium?

[Fairorchids]

75%

[james mickelso]

But.....most commonly available orchids don't "require" high humidity. The leaves don't care. Just the roots. And if you have tailored your potting media to keep some humidity around the roots between waterings, they do just fine. Most commonly available orchids get along just fine at 35% humidity. Much of the Fall and Winter here averages around 20% to 50% humidity. Mine grow just fine. And flower very well. Here....

These all grow in dry to medium humidity and are watered at most once a week if that much. Yours will grow just fine too.

[euplusia]

Many Cattleyas and Dendrobiums grow well on a windowsill, if it it not directly above radiator heat.
I second james mickelso. The roots are in a (plastic) container, and the leaves can open and close their stomata to control evaporation. Air change rate is more important than constant humidity.

[Optimist]

Catts are more like outdoor plants. They love wind, rain, and bright shade.

[Ray]

I keep my greenhouse at about 85% RH. The plants love it.

The higher the humidity, the more likelihood of algae, molds and fungi. Plenty of decent air movement prevents that, and in a pinch, a periodic dousing with a disinfectant like Zero-Tol takes care of it.