What is the origin of the idiom "green thumb" and when to use it?

The phrase "green thumb" is an idiomatic expression that refers to a person's natural talent or skill for gardening or growing plants. It is often used to describe someone who has a knack for cultivating and caring for plants, and their plants thrive under their care. The term is derived from the literal association of green with healthy plant foliage and a thumb as a symbol of dexterity or skill.