The phrase "green thumb" is an idiom used to describe someone who has a natural talent for gardening or a particular ability to make plants thrive. The origin of the term is not entirely clear, but it has been in use for several centuries.

One popular theory suggests that the term has agricultural roots. Farmers and gardeners noticed that some individuals seemed to have a natural skill for growing plants, leading to the belief that these people had "green thumbs" because their plants flourished and their thumbs were stained with chlorophyll from handling plants.

Another theory traces the origin to the English phrase "green-handed," which was used in the 1930s to describe someone who was adept at gardening or working with plants. Over time, this expression evolved into the more commonly used "green thumb."

While the exact origin may be uncertain, the term has become widely accepted in English-speaking cultures to compliment those with a talent for gardening or nurturing plants.