December isn't too late to add cool season bedding plants to your flowerbed or landscape. Cool season bedding plants thrive with mild days and chilly nights. Most will easily tolerate temperatures in the low 20s and sometimes even the teens with little to no damage.
Cool season plants will bloom in fall and winter, produce a tremendous display in spring, then finally fade out in May as the weather gets hotter. They often produce more spectacular displays in the spring when they're planted in the fall compared to spring-planted cool season bedding plants, so do get to planting these cool season plants now.