Read on to learn more about orchid yellow leaves and orchid diseases.
Are my orchid yellow leaves a problem? This is a very frequent question that we get, "Why are there yellowing orchid leaves?" There are many reasons why leaves turn yellow. Orchids like all other plants age and during that aging process the older leaves will turn yellow and die. Remember we are saying the older leaves of the orchid plant, those toward the bottom.
Let's turn our attention to yellow leaves that are not old and not on the bottom of the plant but newer leaves on the orchid. Some of the other reasons include:
Bacterial or fungal disease on orchid leaves will show itself as irregular yellow spots on the leaf. In other words it will not involve the whole leaf but just spots on the orchid leaf. If there is a black growing edge to the yellow spotting then this is caused by a fungus.
The treatment for the bacterial infection is with Physan which can be purchased at a nursery. For the fungal infection a fungicide for plants or orchids will do fine. Another thing that you can try to use for both bacterial and fungal infections is to sprinkle the infected part with cinnamon. Yes, cinnamon the kitchen spice.
Yes, orchid yellow leaves can be due to too much light. In fact, in the mid day summer sun orchids can actually get burned spots on their leaves. This may be one of the more common reasons for yellowing of leaves. Place the plant in indirect bright light for a while and it will recover just fine. The leaves will remain yellowed and will not turn back to green.
Sometimes too much water can will also cause the leaves to turn yellow. But in these cases there will be evidence of "rot" as well. Sometimes when Phalaenopsis orchids are rotting at the roots the leaves leaves will turn yellow and fall off. Too much watering can cause a fungal infection and this is seen with black areas within the yellow area as seen in this picture.
Stop watering for a week or two and then only once a week after. You need to treat for a fungal infection.
What sort of environmental issues cause yellowing of orchid leaves? The biggest is cold weather. Yes, when orchids are subject to cold weather their leaves can turn yellow due to the damage caused. This can affect the whole leave(s) or parts of them. Also, certain environmental toxins can create this condition such as paint fumes or cleaning fumes. When these are being used be sure to get air circulation moving around the orchids.
As you can see there are quite a few causes of yellowing leaves. Treat the easy ones first unless you suspect a more serious problem like a fungal or bacterial infection. If you have questions consult a good nursery or your local orchid society.