1
general::
Eliminate as inferior, unsuited, or unwanted, as in She was asked to weed out the unqualified applicants. This expression transfers removing weeds from a garden to removing unwanted elements from other enterprises. [First half of 1500s]
American Heritage Idioms
2
general::
Phrase(s): weed someone or something out
Fig. to remove someone or something unwanted or undesirable from a group or collection. (Fig. on removing weeds from the soil.) • We had to weed the less productive workers out one by one. • The auditions were held to weed out the actors with the least ability. • I’m going through my books to weed out those that I don’t need anymore.
McGrawhill's American Idioms And Phrasal Verbs