If you want to know what I think did your Phal in, I can say with confidence, it is not because your house got too cold because of the snow. This does not cause root rot.
Root rot is the result of
overwatering. Overwatering is the actual cause. How? LECA looks dry, but it still retains a lot of water because it is a porous material. You cannot pay attention to how wet or dry LECA looks. You have to pay attention to how long the roots are drying out or staying wet.
This is semi-good news. What this means is that it is within your control to determine how much water a plant can receive to prevent root rot.
The cooler temperatures does contribute to allowing the plant to retain more water than if it is warm. Why?
Capillary action and the rate of
transpiration. There are pores on the leaves called
stomata. For the most part the plant is able to regulate the opening and closing of the stomata. (Click this link to find out the basics on how the plant regulates the opening and closing of stomata:
https://www.sciencemag.org/site/feat...nspiration.pdf.) When the plant keeps the stomata open, it allows water to evaporate out of pores. The warmer the temperature, the more water evaporates out of the pores. Water that evaporates is replaced by water that is pushed up through the plant's vascular system as a result of water's
molecular cohesion. Think of molecular cohesion like a series of water molecules linked up like a train. The top molecules pull the bottom molecules up. (Keep in mind I'm kinda keeping this simple, there's another aspect of capillary action that I did not talk about regarding a chemical property of a water molecule called
adhesion.)
Here's a quote from the following link describing how temperature affects the plant's water control:
"
Temperature – Temperature greatly influences the magnitude of the driving force for water movement out of a plant. As temperature increases, the water holding capacity of that air increases sharply. The amount of water does not change, just the ability of that air to hold water. Because warmer air can hold more water, its relative humidity is less than the same air sample at a lower temperature, or it is ‘drier air’. Because cooler air holds less water, its relative humidity increases or it is ‘moister air’. Therefore, warmer air will increase the driving force for transpiration and cooler air will decrease the driving force for transpiration."
(
https://www.sciencemag.org/site/feat...nspiration.pdf)
If it is cooler, the rate by which the evaporation of water going out through the stomata decreases, which allows more water to stay inside the plant longer. Cooler temperatures also affect water transport because it can decrease the plant's metabolism. This in turn means, the orchid doesn't really need to be watered much if there is sufficient water pressure to maintain the plant's turgor.
Other factors that contribute to water transpiring out of a plant or the plant retaining water is
relative humidity. Here is a quote from the same article that describes this in digestible terms:
"
Relative humidity – Relative humidity (RH) is the amount of water vapor in the air compared to the amount of water vapor that air could hold at a given temperature. A hydrated leaf would have a RH near 100%, just as the atmosphere on a rainy day would have. Any reduction in water in the atmosphere creates a gradient for water to move from the leaf to the atmosphere. The lower the RH, the less moist the atmosphere and thus, the greater the driving force for transpiration. When RH is high, the atmosphere contains more moisture, reducing the driving force for transpiration."
(
https://www.sciencemag.org/site/feat...nspiration.pdf)
Too much water starts affecting the oxygen the plant's cells are receiving. This results in cellular death if this over-hydrated state is prolonged.
In other words, it needed to be watered less.
There is a science to this. While it is difficult to say that if you use however many mL of water under these specific temperatures, and at this RH you are guaranteed success, there is a very detailed explanation for what is happening.
When talking about the proper temperature ranges to place your orchids in, you have to consider where the species that make up your orchid hybrids originally came from in the wild. Phalaenopsis and Miltoniopsis both come from the tropics only because of where the countries they originated from are located in respect to the Earth's equator and in relation to the 2 tropics (Tropic of Cancer to the north of the equator & Tropic of Capricorn to the south of the equator). It is not possible to determine temperature tolerance based on whether the plants originated in the tropics or not
alone. You must also know the elevations that these plants originated from. If the plants originated from are normally found at 0 m - 900 m above sea level in the tropics, they
usually (not always) experience warm temperatures (65 F - 95 F/18.3 C - 35 C) throughout the year. If the plants originated from the tropics and are normally found at around 1,000 m - 2,000 m above sea level, they
usually experience intermediate/moderate temperatures (55 F - 85 F/12.8 C - 29.4 C) throughout the year. If the plants originated from the tropics and are normally found at around 2,100 m - 2,500 m above sea level, they
usually experience cooler temperatures (45 F - 80 F/7.2 C - 26.7 C) throughout the year. From 2,600 m - 3,000 m above sea level in the tropics, the temperatures are
usually around (36 F - 75 F/2.2 C - 23.9 C) throughout the year. (This is a simplified explanation, it can get complicated, and I do not want to go more into things than I already have.)
Phalaenopsis
in general (there are outliers) usually do well in the intermediate to warm temperature range of (60 F - 95 F/15.6 C - 35 C).
Miltoniopsis
in general (there are fewer, if any outliers in this genus, but I want to make sure I cover the bases) do well in the cool to intermediate temperature range of (36 F - 85 F/2.2 C - 29.4 C).
Keep in mind that water freezes at 32 F = 0 C.
Regarding your Miltoniopsis (Mtnps), even though this plant likes moisture, it does not like it soggy. The roots still like some air going to it. Something like medium or large grade tree fern fiber works great on these. There is less need for water, and plenty of air going to the roots. Small grade to medium grade wood chips work great too.
Is my Miltonia Sunset healthy?
Thanks. That's really a whole lecture for botany101 LOL you did help to transfer my knowledge from BIO class to real life exp. Thanks LOL
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