Why are the leaves on my gardenia planet turning yellow?

Could be several reasons. If the yellow is in between the nerves is iron deficiency so add 1tbsp of iron sulfate to the soil and water after. It probably needs a complete fertilizer too.

Just water when the soil starts to dry

It needs a lot of light and may be outside if it is not freezing (it stands some frost if grown outside)
Why are the leaves on my gardenia planet turning yellow?
the reason your plant is turning yellow is because it is receiving to much heat or direct sunlight....... or it may be sick with a plant type disease
Reply:Due to infection or inadequacy of sunlight/ water, green coloured chloroform is transformed in to yellow colour.
Reply:Gardenias like acid soil. If you live in an area where the soil has a high Ph you may need to add some acid to the soil. You can find these preparations in most garden stores. Most Gardenias that are over two years old will tolerate some freezing weather. We just had a couple of nights at 24 degrees and my Gardenias are fine. Although some of the leaves may turn yellow and fall off. It should recover by spring.

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