Question
Hello again,

"High humidity simply limits the amount of water that evaporates or leaves through the leaves. Thus, in very dry air (the desert or indoor artificially heated homes), plants lose more water than usual through evaporation. Increasing the humidity will slow that evaporation.

However, even in high humidity, a plant continues to use water and most of that water enters the plant through its roots, not through its leaves."

Referring to what you said above and the additional factors listed in your response, does it follow that roots don't need to uptake as much water in high humidity because transpiration is reduced? If that is correct, what change are we taking about. I realize there will be variances between plant species based on anatomical and physiological differences, however, for my purposes a broad general range will suffice.
Thanks.
T.W.
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The text above is a follow-up to ...

-----Question-----
Hi Will,

I'm very impressed by your previous answers and hope you can provide me with general information about how much moisture plants take in from the air. I understand water requirements are less in winter when growth slows but wonder if plants take in significantly enough atmospheric moisture in high humidity to alter watering practices. It rains all winter where I live and humidity is usually very high. These plants will remain out on the balcony, sheltered from rain, for most of the winter except when frost threatens.

Thanks for your insights!

TW

-----Answer-----
Hi there,

Most plants are not really designed to absorb significant amounts of water through their leaves, although there are some odd exceptions.

High humidity simply limits the amount of water that evaporates or leaves through the leaves. Thus, in very dry air (the desert or indoor artificially heated homes), plants lose more water than usual through evaporation. Increasing the humidity will slow that evaporation.

However, even in high humidity, a plant continues to use water and most of that water enters the plant through its roots, not through its leaves.

How much water a plant uses depends on light or growth rate, temperature, and humidity. In winter, growth rate slows because the light is reduced, but if the plant is indoors in very dry air, then the plant may actually use more water than in summer. But on your deck in winter, you will have reduced light (growth), cool temps, and high humidity. All three factors will work to reduce water use in comparison to warmer summer days.

How often you should water does not lend itself to a formula as all of these conditions can vary from day to day. Thus, the best practice is to check the moisture level of the soil with your finger to determine when a plant is ready to be watered.

Please let me know if any of this is unclear or if you have any additional questions.

If this information has been helpful, please take the time to give me a rating and nomination.

   
Regards,
Will Creed, Interior Landscaper
Horticultural Help, NYC

You can E-mail me directly at: [email protected]

Visit my website at  www.HorticulturalHelp.com  

Answer
Yes, it is true that plants lose less moisture through their leaves (transpiration) in high humidity and that reduces the plants need for moisture around the roots. Just how much is hard to specify.

In general, during the shorter, cooler days of winter it is best to allow the soil to dry out a bit deeper into the pot than  you would in summer. In very damp, cool environments you may need to water very infrequently.

Will Creed