What Happens When an Orchid Gets Too Cold?

Phalaenopsis orchid with cell collapse due to cold shipping temperatures 

Most orchids are tropical and enjoy temperatures between 60-80 degrees Fahrenheit. Like most other plants (and animals), orchids are used to daytime temperatures being a bit higher than nighttime temperatures. In fact, cooler nights and a bigger discrepancy between day and night temperatures induces blooming in many types of orchids, including phalaenopsis. That’s one reason many orchids bloom during the winter, despite the reduced hours of light. 

Close up of the damaged leaf from the above orchid

However, orchids can get too cold. If you have a yard or garden, you’ve likely noticed what happens to annual plants when it freezes outside—they often turn slimy, almost as though they’ve melted. In a sense, they have, as the cold temperatures kill the cells that comprise leaves and stems. The same thing happens to orchids when they’re exposed to cold temperatures, although their leaves usually don’t turn to mush. The waxy leaves of an orchid such as a phalaenopsis suffer something called mesophyll cell collapse, which manifests as pitting, scarring, and/or discoloration.

Cross-section of leaf (photo credit: ELaurent, CC BY-SA 4.0, via Wikimedia Commons)

The outer layer of an orchid leaf consists of epidermal cells. Under that are two types of mesophyll cells, which comprise about 85% of the total leaf tissue. Mesophyll cells contain chloroplasts and act as the control centers for photosynthesis, so their health is essential to a plant’s overall health. When these cells are damaged and collapse, the plant will exhibit external damage and may have difficulty absorbing necessary nutrients.

Pitting/scarring on the underside of a phal leaf due to cell collapse

Cold temperatures (below 50 degrees Fahrenheit) that accompany a power outage, cold weather/bad packaging during shipping, or even a drafty window in winter could be enough to cause mesophyll cell collapse. Watering an orchid with very cold water (below the same temp of 50 degrees F) can also cause this problem. Cell collapse cannot be reversed after it happens, so prevention—with the help of thermometers—is key. Younger plants and leaves are more vulnerable to cold temperatures and cell collapse, so they’re the ones to watch most closely. The extent of damage varies and depends on how cold the plant gets and for how long. Longer exposure to colder temperatures will result in more severe damage, and vice versa.

Severe discoloration and scarring from mesophyll cell collapse on the underside of a phalaenopsis leaf 

There are two particularly tricky aspects of mesophyll cell collapse. The first is that the damage, unless very severe, likely won’t be visible until a few weeks after cold exposure. That means it might take an owner a while to realize there’s a problem. The second difficult detail is that the leaf damage caused by cell collapse also resembles other plant issues, such as viruses or pests. Viruses and pests can spread, but cell collapse can’t, so it’s important to know which you’re dealing with so you can keep your entire collection healthy and happy!