Peonies flower once a year, here in NW Missouri from late April to early June, which equates to roughly 7 weeks. The sequence of flowering is graded into 7 distinct periods: very early season, early season, early midseason, midseason, late midseason, late season, and very late season. The calculation starts with the opening of the first flower of the season.
It is calculated from the midpoint, week 4, which is defined by the bloom time of ‘Red Charm’. Each cultivar is assessed by how much earlier or later it blooms compare to ‘Red Charm’. The resulting scale is virtually identical to that of the Bloom Period model. The earliest week is 1, while peonies of week 7 are the last to flower. Bloom week notations with more than one number indicate a long bloom time which sometimes reaches across several bloom weeks.
For more information please click the hyperlink (highlighted in green color) or simply click the image of the variety you are interested in.