black thumb

/B L AE1 K TH AH0 M/
noun
  1. 1

    A lack of skill in gardening; brown thumb.

  2. 2

    (more generally) An inability to make animals or plants in one's care thrive.

  3. 3

    A person with a black thumb.

  4. 4

    Used other than figuratively or idiomatically: see black, thumb.