A green thumb is a natural talent for making plants grow. She has a green thumb, no green thumb at all, a real green thumb.
It is the American form, and the British say green fingers for the same gift. It credits luck or instinct rather than the reading and patience that actually do the work.
1phrasegreen thumbA natural talent for making plants grow.
“Everything on her windowsill thrives, which is a green thumb if ever there was one.”
green thumb is a phrase.
Also accepted in games: green fingers
Practised in Idioms