Hellebores are very hardy and although most species will grow and thrive in Zones 4 through 9, we are not sure how well they would tolerate Zone 3 or Zone 10. We have customers who are growing our plants in 49 of the 50 states, everywhere but Hawaii! While many of the hellebore species have been grown in the US for a number of years the interspecies and intraspecies are fairly new to the gardening public and have not been thoroughly tested. These plants were very rare and available only to a select few ten years ago but are now sold in the millions thanks to micropropagation. While some vendors list H. x ericsmithii and H. x balardiae clones as hardy to zone 4 we are inclined to err on the side of caution listing them as zone 6. We'd rather a customer be surprised that a plant lives and thrives than disappointed that it died.
Although very tolerant of sunlignt, most hellebores prefer to grow in summer shade or partial shade in the warmer parts of the country, and do well on hillsides or sloping areas. When planting outside we recommend preparing the area beforehand if possible and improving drainage if needed. The plants also grow and display their flowers well in raised beds as long as the beds are deep enough to allow for at least eighteen inches (18”) of soil for rooting area for Lenten Roses. The interspecies hybrids H. foetidus and H. niger have shorter root systems and will grow quite well in containers. H. x hybridus, the Lenten Rose will also grow well but they must have large containers with lots of root space.
Helleborus x hybridus, true H. orientalis, H. niger, H. x nigercors, H. x ericsmithii, and H. foetidus, are evergreen, while H. argutifolius, H. lividus (tender), H. x sternii are evergreen in warmer climates, foliage can die back to ground level in colder areas. H. multifidus, H. purpurascens, H. viridis, H. odorus, H. atrorubens, H. dumetorum, H. cyclophyllus H. torquatus and H. croaticus are considered deciduous, although in some garden situations these may retain some foliage. Helleborus atrorubens is the first species to begin to go dormant in our garden, followed by H. thibetanus. In some areas (our Zone 7 garden among them) H. purpurascens and some strains of H. multifidus begin going dormant in August or September. Since buds are formed in summer, stress such as withholding food and water can reduce blooms in winter. When the nights begin to cool off a bit, in late August or early September, H. x hybridus plants begin to put on new leaves and seem to experience a growth spurt. We recommend cutting off flowers after seeds have ripened, and cutting back the old leaves of the evergreen species just before the flowers appear in winter to better appreciate the beautiful blooms.