Why are my Meyer lemons leaves suddenly looking patchy and falling? This is happening on the older leaves which used to be dark green but are now turning a lighter green. We are in Toronto, and the weather has been 35°+ recently so we keep it outside in direct sun for 6+ hours. Watered thoroughly every few days or when dry. Potted and indoors. Sits in well draining soil and was fertilized 2 weeks ago with a citrus fertilizer (slow release) in the form of a spike. No sign of pests or bugs. Older leaves at the bottom have been falling off recently.
Hello, I am sorry to hear that your Meyer lemon tree is ailing. Have you had this plant for very long? And more specifically have you every put it outside in direct sun before? If you have had your plant indoors in a controlled environment and then recently put it outside in direct sun, with the extreme heat we have been having, I would guess that your plant is under stress. You might want to try moving your plant to a more shaded position, one where it gets morning or afternoon light, and not experiencing the full blast of the sun all day.
Citrus plants are somewhat a fussy lot, they need a balance of high humidity but cannot tolerate soggy soil. They do enjoy a high potash fertilizer (tomato type). They also do best in temperatures between 16 and 22 C, they dislike drafts or overheating.
It sounds as if you have been careful not to let the plant become waterlogged and have given your plant the correct fertilizer, so you are on the right track, but I noticed in the photo you have provided that the leaves seem to be turning a pale green. This could be a sign of chlorosis. This occurs when the plant is not receiving adequate chlorophyll.
I am including a link that describes this condition and offers some remedies. Good luck with your lemon tree!
https://web.extension.illinois.edu/focus/index.cfm?problem=chlorosis