Question
Would it be okay to mist a greenhouse containing orchids, nepenthes, and other water sensitive plants with tap water? Just for the purpose of cooling the greenhouse? What if the mist was not directly over the plants?

Answer
Hi Caleb,

Misting works really well to cool a greenhouse.  However, misting generally works in areas with low humidity.  If you live in the south or where the humidity is generally high, misting might not cool the greenhouse sufficiently.  With high humidity, you'll also need to increase air flow out of the greenhouse to increase the evaporation.

You can use tap water if your mineral levels are low enough.  If it is too high (above 100 ppm), you'll quickly end up with mineral deposits all over the greenhouse.  Some of it will end up on the plants, even if you didn't direct it over them, because the fine mist will travel with the air current.  We sometimes use a misting fan when the temperature gets too warm, but we have it hooked up to our reservoir of RO water.

Another option is using a swamp cooler.  These devices uses water to cool the greenhouse, but it doesn't splatter it all over the place.  Just like misting, it works best if the humidity is relatively low.

Good growing!
Jacob Farin