Understanding Helleborus
September 11, 2013 
Hellebores (Helleborus spp.) have been horticulture’s hot stock for the last few years and every year there are more introductions on the market. While many hellebores are long-lived, drought- and pest-resistant perennials suitable for most of our large country, it is important to note that there are several types of hellebores on the market today. There are different species of hellebores, as well as hybrid crosses, each with diverse attributes and distinct cultural requirements. Because each species has different advantages and traits, it is important to understand a bit of the botany to successfully grow and sell hellebores.
Lenten Roses Are The Most Common
The most commonly grown hellebores, Lenten roses, have been available at garden centers for many years. The Lenten rose types were called Helleborus orientalis, which was changed to H. ×orientalis and later to H. ×hybridus. This was supposedly to show that the group is composed of hybrids from several other species, as well as H. orientalis, although sometimes it seems the name changes were done just to confuse us.
The Lenten rose types are almost always produced from seed, and plants are sold as mixed color strains or color groups. Seedlings are variable and should not be sold as clones. The plants require a couple of years after transplanting to reach blooming size. Mature plants can easily reach 36 inches in diameter and nearly that in height as the flower stems appear in late winter.
Although generally regarded as shade plants, the Lenten rose types will tolerate a wide range of growing conditions including full sun in northern regions. This hellebore has a very deep root system, and plants are extremely drought tolerant once established. Winter-damaged foliage may be completely removed before the flowering stems emerge without affecting the plant.
H. ×hybridus has been difficult to micro propagate, and plant numbers are slow to bulk up. There are tissue culture clones available as young plants from the Heuger Company in Germany (as the Spring Promise Series). As the labs refine their techniques, we will see more clones in the coming years. Until that time, we feel the best of the by-color seed strains are the Winter Jewels series from Ernie and Marietta O’Byrne.
Christmas Rose Is A Smaller Species
H. niger, the white-flowering Christmas rose, is valued for its winter blooms and is one of the smaller species. It produces 8- to 14-inch-tall flower stems over plants that slowly expand to approximately 24 inches wide. The plants have quite shallow root systems and do not like to have all of their foliage removed at one time.
This species is easy to micropropagate, and there are several tissue culture clones on the market. H. niger is fertile and seed strains are available, but like all hellebores, the seedling offspring will be variable and should not be sold under the clonal name.
Heuger has introduced clones of H. niger sold as the Heuger Gold Collection. Some of them are H. niger ‘HGC Jacob,’ ‘HGC Joshua’ and one we think is the best of the lot: H. niger ‘HGC Joseph Lempur.’ One advantage of clonal production is being able to produce a group of identical plants, which allows them all to flower at the same time. This is especially nice for plants grown as a pot crop, as you can count on a big block of color for a particular sales period.
Interspecies And Intersectional Hybrids Are Newer Forms
Joining the Christmas and Lenten roses at garden centers is an unusual group known as the interspecies or intersectional hybrids. This group doesn’t appear to have a user-friendly common name yet, but it won’t be long before they are being called something catchy like holiday roses. These newer forms, Helleborus ×ballardiae, H. ×ericsmithii and H. ×nigercors, are seedling crosses. This means they are hybrids between at least two different species that have attributes from each.
One of the parents of all three groups is H. niger. The other parents are H. lividus for the ballardiae group, H. argutifolius for the nigercors group and H. ×sternii for the ericsmithii group. We haven’t found a way to simplify this bit; if you feel a bit overwhelmed, so did we when we first began to breed these plants. In fact, we had to make myself a cheat sheet. we wrote down all the crosses on a piece of paper to keep in my pocket. These hybrids are increased by micropropagation because they are almost always sterile.
Attesting to their H. niger parentage, the new clones open white or cream with flowers that face outward at about 90 degrees. This is the feature most often lauded in the popular press, sometimes referred to as “upward facing.” As the blossoms mature, they go through a series of color changes; the degree and shade of pink varies from clone to clone.
Helleborus lividus is a tender perennial. We cannot grow it outside in our Zone 7 garden. This plant is the pollen parent to H. ×ballardiae and is part of the background for H. ×sternii. It produces dusky pink blossoms and gives its color to many of the new plants.
H. ×nigercors usually opens white and ages to green. As with other hellebores, the deeper colors seem to be more prevalent with cooler temperatures. The foliage can be very different on individual clones; some are heavily veined while others have silvery or bluish-green leaves. Interspecies hybrids resemble H. niger in culture and also do not like a complete “winter haircut.” They have shallow root systems and grow happily in containers. Plants grow well in sun or shade, except in the South where afternoon shade is appreciated.
Cold Hardiness Still Needs To Be Tested
We do not feel that the interspecies or intersectional hybrids have been available in this country long enough to guarantee their hardiness. The plant labels that accompany plugs give hardiness as -20ºF or -30ºF, but personally we would offer a caution.
A plant may survive these low temperatures if there is good snow cover, but in the Midwest, with the wind whistling down the plains and no snow cover some question remains. These hybrids make wonderful container plants that can remain outside year round with a minimal amount of protection during very cold periods. Although helleborus plants may be hardy outside, it is important to remember and remind buyers that if plants have been grown in even minimally heated houses, they will not tolerate being moved outside into subfreezing temperatures after the holidays. These plants must be kept indoors and gradually hardened off before they can be moved outside.
We have barely scratched the surface of the hellebore tribe, leaving more species and even newer hybrids for another day. If the past few years are any indication, it seems there will be a hellebore for every application. Try some this year and see what everyone is talking about.
Richard E. Tyler and Judith Knott Tyler ([email protected]) are co-owners of Pine Knot Farm in Clarksville, Va. They are avid and well-known collectors and breeders of hellebores, and their breeding work with the double forms of helleborus has sparked national interest.
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