Wear the trousers
Be in charge.
An old English folk tale has it that parsley grows best in a household where the wife wears the trousers.
To be 'wearing the trousers' is to be the dominant member of a household. In the days that this phrase was coined that person was normally expected to be the husband and father. The only reason to employ the phrase at all was to relate it to a woman, with the implication that the normal order had been overturned and that a woman was dominant over her husband.
The phrase was known in the USA from the late 19th century. It probably originated there as printed reference to it elsewhere don't appear until well into the 20th century. The Manitoba Daily Free Press used the term in November 1880, in an article about the domestic life of White Indians and their squaws - who we would now call Native Americans:
"The squaws are very beautiful and are as fond of ornaments as Indian women usually are. The women are called ladies and they sometimes wear the trousers or boss the white Indians, their husbands."
See other phrases that were coined in the USA.