Snapdragons (Antirrhinum majus) prefer cool weather. In warmer parts of North America, it's best to treat them as a spring or fall annual. In Zones 6-9, they may overwinter, so a fall planting can be carried through the winter, providing nice bloom in fall and again in spring. Remove plants when hot weather hits. In cooler regions, snapdragons may grow through the summer, languish in midsummer's heat, and perk up again in fall. It's a good idea to remove faded flower stalks to encourage side shoots to form. Also try growing one of the dwarf cultivars of snapdragon such as the Tahiti Series, which remains less than a foot tall.