Why do we mist?
 

I was wondering why do we mist our orchids?

From what I have read, it is transpiration that brings water and nutrients from the roots to the leaves. Transpiration, which is the cooling mechanism of plants similar to perspiration in humans. Well, if there is water on the plant already, how can it transpire?

I do understand that there is a requirement of these plants, that there be some humidity around them and that the humidity should be higher as the temperature gets higher. So it seems appropriate to mist orchids that are outside and/or subject to higher temperatures, as this aids the cooling of the plant which is unable to transpire enough to cool itself, because the plant evolved in a different environment. Also, orchids grown in drier climates would need to be misted to slow transpiration and prevent dehydration. Now, this is based on my understanding of how plants work, but I am not a botanist. I have been just reading as many books I can get my hands on to learn more about how plants, specifically orchids, work.

So is there really a need to mist orchids that are not subject to high temp or low humidity? Would doing so slow the uptake of water and nutrients and thus slow growth?

Dave

Hi Dave,

What you have said is true, but most orchids we grow come from tropical environments where the humidity is high, and are therefore accustomed to high moisture levels around the leaves (this varies though). As most of us live in areas where there is not as much moisture in the air, we have to provide the humidity artificially. Misting is one method, but I call it ineffective in the long term because the effect is short-lived. It is, however, beneficial in the short term, especially with epiphytic plants. Epiphytic plants, in addition, need humidity to survive as the aerial roots and leaves absorb the moisture that way when moisture is not available at the roots. If you have already created an optimum humidity level, misting is not necessary and may in fact be harmful for the reasons you stated; 100% humidity is generally not a desirable condition for long periods of time. I hope this answers your question.

I barely mist anymore, it is not very effective for raising humidity. The only time I mist is if there is long hours of direct sunlight to cool the leaves.
Some beginners mist so much that plants rot......

Hi Dave :)

There are some 'chids who could do without misting but...anything that has hanging roots or is mounted need their roots saturated.

Vandas especially need this extra attention as they do not have bulbs to store water so they only get what we give them ;)

First we have to understand that unlike perspiration, transpiration occurs both ways - in and out.

However, the out is not a cooling mechanism as much as a "breathing" one. If it was, we would see a plant tend to shrivel rather than burn.

Likewise, the in is more for "breathing" than for liquid absorption. The number of stomata on a leaf surface are usually relatively few in orchids (compared to other plants), which is an adaptation to prevent the loss of water, which goes right along with the need for high humidity. Interestingly, phalaenopsis, some of the more humidity-loving plants, have some of the fewest leaf stomata, they tend to be closed in the daytime, and have also developed something of a "waxy" coating on the leaves to further slow moisture loss.

Besides, when one mists plants, the goal is to increase the humidity, so we should be misting into the air, and not onto the plants. Wetting the plant surface actually slows the humidity enhancement, and the surface area of a gazillion tiny droplets is a LOT higher than that of a wet leaf.


You might want to read this:Evaporation

Thanks guys, now I have learned something.

The misting we do should be directed at the air around the plants, not on the plants. This is most effective in a closed (for the most part) environment where the humidity will be kept around the plants. It also makes sense that misting would cool the area around the plant.

Misting aerial roots is completely different as this is the only source of water and nutrients for such orchids.

What I found most interesting is that orchids have less stomata, as compared to other plants. Which partly explains why orchids grow so slow.

Dave