Humidity Level

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Ray

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In the "Ceiling Fans" thread:

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:

  1. Is ultra-high humidity an issue?
  2. Is there a practical upper limit?
  3. Does transpiration even play a role in nutrient uptake?
Or are we just stuck with plants that have slow uptakes, hence a lower demand for nutrition than others?

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 would guess it has to do a lot with the native climate of species -- some grow in very high humidity, and some are in quite dry conditions.
 
I looked up the weather for Borneo:
• Sandakan, Borneo's climate receives an average of 3040 mm (119.7 in) of rainfall per year, or 253 mm (10.0 in) per month.
• On average there are 178 days per year with more than 0.1 mm (0.004 in) of rainfall (precipitation) or 15 days with a quantity of rain, sleet, snow etc. per month.
• The driest weather is in April when an average of 101 mm (4.0 in) of rainfall (precipitation) occurrs across 11 days.
• The wettest weather is in December when an average of 465 mm (18.3 in) of rainfall (precipitation) occurrs across 20 days.
The average annual relative humidity is 71.7% and average monthly relative humidity ranges from 67% in September to 77% in January.
• Average sunlight hours in Sandakan, Borneo range between 5.1 hours per day in January and 8.8 hours per day in April.
• There are an average of 2448 hours of sunlight per year with an average of 6.7 hours of sunlight per day.
• There are an average of 0 days per year with frost in Sandakan, Borneo and in January there are an average of 0 days with frost.
 
In the "Ceiling Fans" thread:
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 day


Not sure how much of this is accurate Ray.

Leaves of many orchids have relatively large surface areas compared to true dry habitat plants, and I've read that stomata are light triggered to open when exposed to certain red or blue light frequencies (regardless of air humidity state). The leaves of even the tough leaved multifloral paphs are similar in "waxiness" to various lily or iris monocots that are also not xeric adapted.

Their durable structure may be more of an adaptation to withstand mechanical damage from pests/disease or repell excess water (as in off a ducks back) rather than for water retention.

Nature tends to be pretty conservative, so it doesn't make sense for plants to have a bunch of xeric adaptations to live in environments that maintain high relative humidity levels.

Bromiliads have even tougher, stiffer, waxier leaves than most orchids, and they are meant to retain water in their cups, and come from high humidty/rainfall areas with a diverse population of amphibians that are very sensitive to water loss.

Interestingly bromileads seem to be much faster growers than orchids too.
 
My target of 70% is also based on experience.

My first couple of years without humidity control had much slower growth and higher mortality than with humidity control. It was like throwing a light switch when I forced the humidity up.

So no telling???
 
In the "Ceiling Fans" thread:

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...


The amount of nutrients available to epiphytic plants is probably pretty low anyway, so no point in having a fast transpiration rate to take advantage of a nutrient impoverished environment.
 

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