May to September is the obvious sweet spot. The Blühendes Barock gardens are at their most spectacular in May and June, when the formal plantings peak and the Baroque-in-Bloom festival fills the grounds with floral sculptures. The Ludwigsburg Schlossfestspiele runs concerts and opera through May, June, and July — easily the cultural high point of the year.
July and August are warm and sometimes crowded with school holiday families, especially in the Märchengarten. September is quieter and the gardens still look good. October brings the Pumpkin Festival in the Blühendes Barock — a surprisingly serious affair with elaborate pumpkin sculptures and a wide variety of squash dishes in the cafes.
November and December are dark and often grey, but the Christmas market on Marktplatz from late November through Christmas is one of the more atmospheric in southern Germany — the baroque facades and the modest scale of the square give it a more intimate feel than the bigger markets in Stuttgart or Nuremberg. January to early March is the quietest time; the palace remains open year-round but the gardens are shut.