Evapotranspiration question

[camille1585]

Originally Posted by estación seca

Many, many orchids open their stomata mainly at night, when it is cooler, and evapotranspiration is less. In this they are like most cacti and most succulents. They are able to take up water from their roots throughout the Sun's journey around the Earth, but it is more important for it to be available at night, when they are losing water.

For this reason most succulentists recommend watering in the evening. I would also suggest this for people growing orchids in low-humidity climates, though it contradicts most advice, which is to water in the morning. This advice, however, comes from people growing in wet greenhouses, which must be kept closed to retain heat. Plants in low-humidity environs are dry within an hour or two, even if the crowns are soaked.

I don't think it's that many. Thick leaved orchids, like Phals, Vandas, and Catt alliance, tend to be CAM photosynthesizers. But most of the thin leaved orchids are in large part C3. A handful of orchids are known to be C4 photosynthesizers, but I think that metabolic pathways of orchids are poorly understood. I do remember reading that some orchids are facultative CAM, and will switch to more efficient C3 when there is plenty of water available, and I think Phals fall into that category. Though I agree that in low humidity environments you can probably get away with watering in the evening as long as the plants are not wet.