Soaking in the night?

[Dorra]

I took up the courage to ask here about the cultivation procedure. For many species of orchids, it is important that the roots dry before the night. And get... many orchid lovers describe how they soak orchids all night.
The general physiology of plants shows that plants absorb water actively and passively. Active downloads require energy. In the dark, it comes from respiration, but at the same time, the need for water intake decreases. I understand that there are differences in the photosynthetic metabolism between C3, C4 and CAM... and the orchid includs in the latter type.


Hence my questions... what does the science say about this? And how much does the orchid absorb water at night when it is dark and photosynthesis is stopped?

[estación seca]

Don't fear! People are generally nice here. The moderators pay attention to that.

I don't think it's true that most orchids need to have dry roots by the evening. Many orchids prefer staying moist most or all of the time. However, when growing in cooler than ideal conditions, or with extremely high relative humidity, there may be less chance of fungus or bacteria attacking if they dry out occasionally. It is recommended that bare-root Vandas dry by nightfall in very humid environments. I think in a lower humidity environment like a home this isn't critical as long as they dry at some point between waterings. In habitat Vanda roots stay wet through entire wet seasons.

Different orchids use different amounts of water and have different watering requirements. Pay attention to your plants in your conditions and you will see this.

Most plants will absorb water whenever it is available. Many orchids open their pores at night to take in carbon dioxide. This is also a good time to water if conditions are otherwise appropriate. Most homes have a lower relative humidity than in orchid habitat. For this reason a long soak is better able to provide plenty of water. Another reason for an overnight soak is most people use the sink during the day, and an overnight soak happens when people are sleeping.

So rather than paying attention to the time of day, watch your plants for signs of underwatering. In Phals. this begins with fine linear wrinkles parallel to the midrib. In other orchids leave become leathery and limp.

[Dorra]

Hmmm... I treat my several dozen Vandas a bit differently... soak until the velamen turns green and saturated with water. Once the velamen is saturated, the orchid will no longer drink water. To drink more, the velamen must dry out. So sometimes it takes an hour and sometimes it takes 15 minutes.
But that wasn't my question. What I'm wondering is what is the water absorption and how much at night when it's dark compared to the day?

[Dimples]

The recommendation to water earlier in the day is also to help ensure that the leaves and other parts of the plant dry off before the indoor temperature (and air movement) drops at night in most homes. Yah, the roots will technically be dryer by nightfall if you water in the morning, but excluding things like vandas that NEED to dry out rapidly, the pot conditions aren’t going to change enough after 12-hours for the timing to matter much.

I water whenever I get around to it, and am a little more careful about avoiding foliage if I’m watering in the evening. If I could plan it out better, I’d be watering around 3pm so the foliage is all dry by the evening but the plants have all the water they want overnight. Afternoon watering helps cool things down when it’s hot-hot too.

[Leafmite]

As said, some orchids are more prone to fungus issues if water sits on their leaves, especially in cooler temperatures. In the summer, when my plants are outside, I water at night to give the roots time to absorb the water because, on a hot day, the medium dries quickly. In the winter, I water during the early part of the day as it is warmer and the leaves will dry quickly if I get water on them (I am careful not to get water on Zygopetalum, however, as they tend to be prone to fungus issues).

[Jmoney]

its been reported that vandas are CAM plants meaning they preferentially take up water after the sun goes down. The actual mechanism is more complicated than that. I tend to spray my vanda (roots, not leaves) in the evening but I cannot say if that translates into better growth than if they got watered daytime only. to my knowledge only some orchids are CAM

[rbarata]

In general, I really don't care about it. In fact, I do most of my watering at night.
But it all depends on the growing conditions and/or climate.

[estación seca]

It is true the velamen can only hold so much water, but it does not need to dry out for the roots to absorb more. Water can continue being absorbed as long as the roots are submerged in water. At one time I grew bare-root Vandas in vases. Submerging the roots in water overnight led to much greater water absorption than just getting the velamen very wet.

[SG in CR]

Originally Posted by Dorra

Hence my questions... what does the science say about this? And how much does the orchid absorb water at night when it is dark and photosynthesis is stopped?

I don't know any studies that address that issue specifically. But, from a purely pragmatic point of view I doubt it matters. It rains at night in the tropics. Orchids have evolved to not only deal with it but take advantage of it.

In my personal experience, when humidity levels aren't high, watering at night seems to be more effective than in the morning. Which makes sense to me as the lower temps mean the plant has more time to absorb the water before it dries out. Though my plants are outdoors and I water with a hose, so indoor cultivation may differ.

[Ray]

Originally Posted by Dorra

Once the velamen is saturated, the orchid will no longer drink water. To drink more, the velamen must dry out.

That does not seem correct to me.

The velamen is just a layer of dead cells that act as a sponge. There are multiple layers of cells under it that manage the transfer of water and nutrients from the velamen to the vascular bundle for transport throughout the plant. I imagine that transfer stays active as long as there is something in the velamen to transfer.