I have a magnolia 4 years old in a pot in a conservatory. Its leaves have started turning yellow in patches. Can you tell me what is wrong with it?
Answer: Without more information I cannot really give you a definitive answer. There could be multiple reasons why the leaves are yellowing. Lack of water or too much water can cause similar reactions so be sure you are keeping it evenly watered and not over-watered, especially. If the yellowing is occurring in the tissue portion of the leaf and the veins remain dark green, then your plant could be experiencing chlorosis, where the plant is lacking iron because the pH level of the soil is too high (above 6.5). You should test the soil pH to confirm this. You say this plant has been in a pot for 4 years, so it’s possible that it’s simply pot-bound. As a tree that prefers to have its feet planted firmly in the earth, it could be that it isn’t receiving sufficient nutrients after 4 years in the same soil and it might be as easy as repotting in a slightly increased size of pot to accommodate the expanded root growth. If repotting, give it some acid/iron-based fertilizer, we recommend a produce like Hi-Yield Azalea Fertilizer to give it the required nutrients for acid-lovers.
One other possible cause could be a soil fungus, Verticillium wilt, but you would want to take a sample leaf and a sample of the soil to your county extension office to verify.
If this does not remedy the problem, then please provide more information, such as your location, a photo of the tree and a problem leaf, and information about its environment.