Why does my mature Michelia figo always have so many yellow leaves?

Question

Now that I’ve read your article, I can see the error of some of my ways, but the bush turned small tree at 5 feet high, is 10+ years old and today I was wondering if this is simply what happens this time of year (North County of San Diego County; Carlsbad/Vista/Oceanside tricity area) especially considering that the yard is mature, the plant is no longer getting as much sunlight as in the past. I’ve tried giving it iron but it has never helped the yellowing issue.

Answer 1

The plant is evergreen and should not turn completely yellow this time of year. However, the banana tree is susceptible to chlorosis (yellowing). A high soil ph could be a factor since it prefers an acidic, organic soil. Nitrogen especially and other nutrient deficiencies can cause yellowing. It's best not to think and fertilize in terms of a specific nutrient, but rather complete nutrition. Soil testing and prescription amendments are best, but general purpose blended fertilization is next best.

https://www.gardeningknowhow.com/ornamental/shrubs/banana-shrub/how-to-grow-banana-shrubs.htm