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Your cymbidium leaves may be turning yellow due to natural causes, or to sunlight, watering or temperature issues. Bugs and diseases may also be involved. From my own experience, the main cause of yellowing leaves is actually too much light. Naturally, they would live under the canopy of trees so filtered light is best.
Read on to learn how to tell what the problem is and what to do about it if your orchid has yellowing leaves.
Some of the leave will naturally turn yellow
Older plants tend to stop sending nutrients to their older leaves in order to focus on new growth. If it’s the older leaves of your plant that are turning yellow, don’t worry.
What to do
Nothing. It’s all part of the natural life cycle of the plant and the leaves will drop of their own accord.
As already mentioned, Cymbidium leaves turn yellow when they’re getting too much light. This isn’t a common problem as these orchids like lots of dappled and filtered light. But maybe your orchid is in a window without a net curtain and it’s getting too much direct sunlight. In this case, the yellow leaves are the equivalent of sunburn.
Note: A cymbidium orchid’s leaves should be an apple green colour. Dark green leaves indicate that it’s not getting enough light and is often overlooked.
What to do
Move the orchid plant to a more shaded location. Or put up net curtains in the window it’s by. The orchid can stand more morning light than noon-time and afternoon light. These plants grow in nature under the branches of big trees, so they’re not used to direct sunlight.
While it’s important that the cymbidium orchid has a higher daytime temperature than at night-time, the temperature swing can’t be too much. Cold temperatures can shock the orchid plant and cause the leaves to turn yellow. I have had this happen when I an orchid on a windowsill in a hall that got quite cool at night.
What to do
Check the coolest temperature that your orchid encounters in its life. This is especially important if you’re leaving your plant outdoors in the summer.
The temperature range at night-time should be between 15˚C and 20˚C. Of course, if you’ve just bought your cymbidium, you don’t know what conditions, possibly very cold, it’s previously been exposed to.
Move your orchid to a warmer location at night if needed.
The most probable cause of your cymbidium leaves turning yellow is watering. But you need to investigate to see if you’re over-watering or under-watering your plant. If the leaves are yellow and still quite plump, you’re probably over-watering; yellow and dry and withered leaves indicate an under-watering problem.
The best indication though is to review your watering schedule. If you’re watering daily, that’s too much.
What to do
See the Water section of the article How to grow and care for cymbidium orchids for more details about when and how to water your plant.
For under-watering problems, change your watering habits as indicated in the guide. Over-watering is a bit more difficult to manage as you need to check the roots of the plant to see if they’ve developed root rot.
Expose some of the roots of your plant. You may be able to push the soil mix aside to see them or you may have to take the plant out of the pot. If any of the roots are black, brown or mushy, they’re infected and diseased. Cut them off.
Note: if your potting soil is water-logged, then do take the plant out of the pot and carefully remove all potting soil from the roots. Carry on with checking the roots. Repot the orchid with new, potting soil and water it in. See How to repot a cymbidium orchid for all the details.
Bugs and diseases
Yellowing leaves can indicate an infestation of bugs or an infection of a fungal disease. This is especially so if the yellow starts off in spots or on the edge of the leaves.
What to do
Check out my Cymbidium orchid pests and diseases article for information about what can befall your orchid to cause the yellow leaves and how to deal with the various problems. Also, visit a similar article for other orchids, Orchid pests and diseases, just in case your orchid has an uncommon pest or disease.