If you like to spend your time up to your elbows in dirt and have the ability to cultivate plants that don’t wither and die, you may have been told you have a green thumb. This is not a medical emergency, but a slang term meant to denote one’s aptitude for gardening and landscaping. But where did the phrase come from?

Both green thumb and green fingers have been common expressions in England and the United States for well over a century, with the Oxford English Dictionary citing use of green fingers as early as 1906 in the novel The Misses Make-Believe by Mary Stuart Boyd. Green thumb, meanwhile, can be pinpointed to a 1937 Ironwood Daily Globe newspaper article, which described the phrase as “horticultural slang.”

Theories abound as to its origins. Some believe it’s a result of handling potted plants, which can often have green algae on the underside that coats hands. Others point to a (likely apocryphal) story about King Edward I and his love of green peas, which were shelled by subservient workers—one would be honored for doing the most work and having the greenest thumb. There’s also the fact that plants contain chlorophyll, a green pigment that can easily discolor your hands.

However the phrase was cultivated, we have a pretty good idea of how it caught on. In the 1940s, wartime Britain enjoyed a popular gardening radio show titled In Your Garden hosted by C.H. Middleton that made use of both green thumb and green fingers.

Why, then, is the phrase focused more on the thumb when all of your fingers are likely to get discolored? It might have something to do with an old English proverb: “An honest miller has a golden thumb.” The quality of corn flour could be judged by rubbing it between the forefinger and thumb. Blended together in the collective consciousness, these two idioms may have resulted in the green thumb we hear about today.

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