Rinse any dirt or debris from the brass planters.
Combine 1/2 cup salt, 1/2 cup flour in a bowl. Gradually add 1/2 cup of vinegar while stirring to make a thick paste. If the paste is too stiff, add a little more vinegar.
Rub the paste on the entire surface of each planter and let it dry -- it should take about 45 minutes to an hour.
Rinse the planters under warm running water while rubbing gently with a microfiber cloth.
Mix 1 cup of baking soda and 1 cup of water to make a thin paste. Rub the paste on the cleaned brass to neutralize the vinegar acid, then rinse thoroughly.
Buff the cleaned brass with a dry microfiber cloth until shiny.