Every year, local gardeners see pansies, violas, dianthus, snapdragons, and other flowers whose peak blooming season is in March through May. Invariably, these gardeners then go out to nurseries in April, purchase these plants, and plant them, wishing to recreate this beauty in their own gardens. Unfortunately, they're disappointed when their plants never reach the spectacular results they saw.
There's a good reason. Most of the mid to late spring displays of cool season bedding plants were planted last fall, or at least by late winter or early spring. Early plantings allows bedding plants to develop into larger plants with robust root systems by the time April's crescendo of blooming season arrives.
Bedding plants that are planted in April will never reach the beauty of those planted early in the seson. The problem is that April is very close to the end of the cool season, with the warmer high temperatures that signal the beginning of summer and the gradual decline of cool season bedding plants.