Edema on Orchid Leaves:
What it is and How to Treat it

Every once in a while, you’ll encounter some spots on an orchid leaf that look either like transparent blisters or brown scale spots that don’t come off when rubbed. These could be edema so don’t reach for the pruning shears quite yet. Edema is not contagious and is not potentially a harm to your orchid.

Why does edema take place in the first place? Edema on orchid leaves appears for two reasons: (1) the orchid’s roots absorbed much more water than would let out by transpiration and the excess created blisters on the leaf, or (2) the environment is a hotter temperature than the orchid leaf and during gas exchange, instead of transpiring, the leaf absorbed humidity in the air. Let’s take these examples one at a time, but first, let’s look at what edema on orchid leaves looks like.

What are the characteristics of Edema on Orchid leaves?

Edema on Orchid Leaves
Image credit: File:A and B Larsen orchids - Oncidium forbesii DSCN0403.JPG" by Arne and Bent Larsen, Haarby, Denmark is licensed under CC BY-SA 2.5 
Edema can either be a transparent blister-like effect, as if some chemical reaction made the plant cells to expand into a third-degree burn.

When this happens, under the elevated plant tissue, there can be slight discoloration, appearing to be slightly yellowish-white.

Edema can also look extremely similar to scale, an insect that likes to form a brownish-black spot on the leaf. 

My Story with Edema on the Orchid Leaf

This happened to me a few weeks ago.

I ordered an orchid online and after going through the scenic tour of six days in the mail, it finally arrived. I have no idea why they watered this poor orchid to the extent it was when it arrived, but it still was drenched—the flimsy, plastic pot dripped heavily when I squeezed it.

It was planted in sphagnum moss, so I have a good feeling that at this nursery there was really no watering schedule, but a heavy misting program in place. That’s fine, but when the orchid was drenched for shipment, then placed in an enclosed box with no light, there was minimal transpiration and evaporation through the leaves.

With no sunlight the cell’s activity was less, requiring less energy, therefore less water. Yet, the poor dude was soaked.

Inevitably, the next day little white/transparent bubbles broke out on the leaves. Was I upset? No doubt about it, but the orchid was worth it. I won’t be returning it, but I also won’t buy there again.

Why does Edema affect the orchid leaf?

These blisters, called Edema, occurred in this case because there was a sudden supply of water that the orchid was not used to. Orchids become “creatures” of habit, and will somewhat adequate themselves to your watering schedule.

You still have to follow the general guidelines, but if you take a day or two without watering, and this is continual, they can adapt to that without dying.

In this case, the orchid was adapted to receiving a heavy misting several times a day. The water droplets kept the sphagnum moss moist and that was enough for it to survive. Yet when it was watered, drenched and drowned in preparation for shipping, the roots weren’t prepared for that. They absorbed the water as they would normally, but absorbed ten times as much.

The leaves, on the other hand, couldn’t release the excess water in the same amount of time. Since there was no sunlight, the orchid required less energy, with no heat, transpired less. It actually gets pretty cool in airports and transportation stalls.

Anyway, all the excess water is now inside the plant and can’t escape. This can result in two things, if not both.

(1) The extra tension inside the orchid leaf will cause the leaf to split. There is water pushing against the plant cells, forcing their way to the outside. Yet, the stomata are closed—stomata are the breathing mechanisms of the orchid, tiny pores where gas is exchanged.

(2) The other result is in the blistering of the leaves, which is called edema.

Difference in temperatures during watering can cause Edema on Orchids

Now going through a period of drought then suddenly being watered isn’t the only reason orchids will display edema. When winter comes around, or it’s a cool cloudy day outside and the inside temperatures drop you will need to water less. The orchid will not be as active in root production, leaf growth, and internal demands of energy, therefore, the orchid will require less water to survive.
Please note: I write about indoor orchids and that is my reference, since I can’t grow orchids outside in Kansas weather. My scope of reference is for indoor orchid cultivating. I’m not an expert by any means, just a person who’s trying to still learn…

So when you read these guides, take them with a grain of salt for outdoors. For that part, I really have to heavily rely on research alone and not my experience.
Amanda June Matthews
My Home Office: Where I grow my orchids
Image Copyrighted by Orchideria 2020

Hey, that is really a pic of me, so please don't copy and paste my pic around the net... #Respect I highly appreciate it.  You can check my Instagram page, if you want more pictures of how I care for my orchids indoors. I feel "safer" posting personal pics there than here. Naive... I know.

Anyway, back to Edema...

If you maintain your normal watering schedule, but the environment around the leaves is cooler than the leaf itself, water won’t evaporate. If anything, when the stomata open at nighttime, the orchid will absorb more humidity from the air than release it. It’s all about a temperature imbalance between the leaves and the environment. This orchid will become saturated, not being able to release all the water it absorbs and forms edema.

How do you treat edema on orchid leaves?

The simple answer is you don’t. The spots can’t be rubbed off, and that is good because if they could, you’d be dealing with scale—not edema. But the leaves will not return to normal after the edema has occurred. You’ll have those as an ever reminder to not do whatever you did in the first place.

In a couple of years the orchid leaf will fall off and a new one will grow, so it won’t last forever.

If you have your orchids outside, and it is cloudy and cool, then the orchid will need less water. Sometimes it’s preferred to not water on that day, and wait until a hotter, sunnier day if possible.
Further Reading Suggestions:

Don't just take my word for what is written here. Continue researching other articles about edema on orchid leaves, because everyone has a different point of view and unique techniques that work for them. Here is another article from other websites if you'd like to continue your research on edema on orchid leaves:

"Edema – Blisters on Orchid Leaveswritten by Sue Bottom,  published by St. Augustine Orchid Society talks about edema and has some pictures that are really worth taking a look at. It's a 5-page PDF file that opens when clicked on.

Happy Cultivating!
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