In the "Ceiling Fans" thread:
That brings up a question I've had for a while:
In terrestrial plants, transpiration is the driving force for liquid uptake, and along with liquids come the mineral ions. That means that excessive humidity, which reduces moisture loss, will actually slow nutrient uptake and reduce the plant's growth rate. That is well-established in the commercial greenhouse-growing industry.
As orchids have evolved to minimize transpirational moisture loss though waxy coatings on leaves, low leaf surface area, fewer leaf stomata, or keeping them closed in the daytime:
Todd Zimmerman once told me that epiphytic orchid "sap" is only about 25% of the concentration of that for most other plants. maybe that's just part of the evolution...
I like to keep mine at >70% with no real top end to worry about.
Some species/hybrids do fine with extended periods in the 50 to 60% range (mostly parvis during the shorter times of the year.
Below 50% and you'd be chasing your tail trying to keep up with watering, and its a stress for the bulk of orchids.
Unless your GH is very well sealed, and use gas instead of electricity to heat, you may be amazed has to how easily humidity can drop to very low levels in the winter. Or just about year round in the SW USA.
That brings up a question I've had for a while:
In terrestrial plants, transpiration is the driving force for liquid uptake, and along with liquids come the mineral ions. That means that excessive humidity, which reduces moisture loss, will actually slow nutrient uptake and reduce the plant's growth rate. That is well-established in the commercial greenhouse-growing industry.
As orchids have evolved to minimize transpirational moisture loss though waxy coatings on leaves, low leaf surface area, fewer leaf stomata, or keeping them closed in the daytime:
- Is ultra-high humidity an issue?
- Is there a practical upper limit?
- Does transpiration even play a role in nutrient uptake?
Todd Zimmerman once told me that epiphytic orchid "sap" is only about 25% of the concentration of that for most other plants. maybe that's just part of the evolution...