Bloom time and flowering duration of Pieris cultivars in two USDA hardiness zones
This study compared the bloom time, cultivar flowering order, and flowering duration of Pieris cultivars in two different USDA hardiness zones. For Pieris specimens established in the landscape for three years in Hopewell, Oregon (USDA hardiness zone 8a) and in Cape Girardeau, Missouri (USDA hardiness zone 6b), we recorded the calendar week of first open flower, and the calendar week when 50% of the flowers had turned brown or aborted. Cultivars that flowered early were all Pieris japonica clones. Cultivars with pink flowers had early or a mid-season bloom times, suggesting that pink flower color may be linked to early blooming. Pieris formosa and some P. japonica clones generally flowered late or very late. In USDA hardiness zone 6b, plants initiated bloom 1 to 8 weeks later compared to the same clones in USDA hardiness zone 8a, and flowered for a shorter duration. Cultivars with late or very late bloom times had significantly shorter flowering duration compared to early blooming cultivars, but only when grown in USDA hardiness zone 8a.
Svenson, S.E. (2018). Bloom time and flowering duration of Pieris cultivars in two USDA hardiness zones. Acta Hortic. 1191, 37-42
Pieris japonica, Pieris floribunda, Pieris formosa, interspecific hybrids