I have no experience with this particular species, but in my experience with others, all tropical (by this I mean any that doesn't survive the Zone 6 -- negative single digit Â°F winter temp and need to be brought indoors) trees and plants develop yellowed leaves and shed some of them during the depth of winter, regardless of how well you are maintaining the growing conditions.
My tea shrublet has dropped all its leaves but are growing tiny new leaves. Downstairs avocado and mango have dropped most of the biggest leaves they grew last summer. Coffee and Jasmine are yellowing and losing about a dozen leaves a week....
Just a thought, although you should still keep an eye out for possible pests like mites, scales, mealybugs, and white flies.
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