Like his both predecessors, Johann Georg was interested in developing a flotilla, but he was also a great patron of the arts and sciences. Under his rule Weissenfels became the leading economical and cultural center in central Germany along with Dresden.
To maintain order during civic celebrations, Johann George created the establishment of Citizen Companies (Bürgerkompanien), in whose service male inhabitants were conscripted.
In imitation of the decorations bestowed by the Fruitbearing Society (of which his grandfather was a head) Johann Georg created on 24 June 1704 a medal extolling knightly virtues "De la noble passion" with the motto "J’aime l’honneur, qui vient par la vertu" (en: "I love the honor that comes from virtue"). The statutes of the order, which the duke wrote both in German and in French, required an irreproachable life and noble birth for admittance.
During the Great Northern War, Weissenfels was occupied by Swedish troops from 1706 to 1707.
Because he died without surviving male issue, Johann Georg was succeeded by his brother Christian.