what is meant by''he had qualified himself for the american diplomacy by leading the German at newport casino for 3 successive years. gardenias and peerage were his only weaknesses'' please expain in simple language

For three consecutive seasons, Washington had led the German at the Newport Casino. This qualified him for American diplomacy. Besides, he was widely known as an excellent dancer in London. However, he had weaknesses for two things-- Gardenias (a kind of flower) and the peerage (the aristocracy).