No moment causes more panic for a beginner than suddenly noticing yellow leaves, falling foliage, or fine webs among the branches. The immediate reaction is often blind activism: frantic watering, excessive fertilizing, or spraying with harsh chemical pesticides. However, when a tree is suffering, the same principle applies as in human medicine: No treatment without a precise diagnosis.

A bonsai never drops its leaves without a reason. Foliage symptoms are the tree’s language—its only way of communicating that a critical imbalance has occurred in its microclimate, root environment, or due to pests…