Of the thousands of cultivars of herbaceous peonies (Paeonia spp.), horticulturists classify them based on the flower form and the bloom time. Early-flowering peonies begin blossoming as early as late March in the Southern U.S., but not until mid-April farther north, according to Allan Armitage, American perennial plant expert and author of "Herbaceous Perennial Plants." Late-season peonies bloom approximately for to six weeks later. Those peonies that bloom in between as appropriately considered midseason types.
Herbaceous peonies, both species and hybrids, prosper where winters provide ample cold when the plants rest dormant. Without ample chilling in winter, plants weaken, and flowering won’t occur in spring. Expect peonies to perform well across U.S. Department of Agriculture Plant Hardiness Zones 4 through 8. A deep, fertile, moist but well-drained soil in a sunny location ensures robust plants. Early-blooming peonies are particularly good in the Southern U.S., since the spring warmth begins so early and the onset of summer heat makes mid to late flowering peonies’ performance disappointing.
As of 2011, there is no standard for describing peonies based on bloom times. Since the mid 20th century, peony enthusiasts collected various data on bloom dates, including Rev. Floyd Miller, Leon Presnell, Don Hollingsworth and Al Rogers. Most recently, Canadian Michael Denny embarked on project to create a more comprehensive listing of bloom dates for old and new cultivars of peonies in North America. His system uses the cultivar Red Charm as the standard midseason peony to compare the flowering times of all others. The hope is to create a standard blooming calendar of all peonies that transcends nursery/breeder and home grower gardens’ latitude or elevation.
Using Denny’s "The Peony Bloom Time Project" data, several species reveal themselves as early blooming types. P. causasica, P. villosa, P. tenuifolia, P. officinalis and P. mlokosewitschi bloom as much as 20 to 40 days before Red Charm. P. lactiflora blooms in midseason and traditionally is used as one parent in making hybrids. Those cultivars with early bloom times most often contain P. lactiflora as one parent and another naturally early-blooming species.
Among the peonies that bloom 13 to 37 days before the midseason blooming Red Charm are: Anika, Sydney, Tinkerbell, Audrey, Little Red Gem, Elfin Beauty, Early Bird, Sunlight, Rose Crystal, Nosegay, Echo, Peter Barr, Papilio, Early Scout, Seraphim, Tranquil Dove, Thumbelina, Early Windflower, Nova, Starlight, Daystar, Playmate, Windchimes, Rushlight, Laddie and Avant Garde. Local weather determines how early and long the blossoms open. Cloudy days and cool temperatures in the 60 to 70 degree range allow peony flowers to remain attractive longer. Hot sunrays, wind and temperatures above 80 degrees cause flowers to endure a shorter period.