Lessons from the NPA Borders: Hellebores

By: Bob Lilly

Bob Lilly is one of the original designers of the Northwest Perennial Alliance Borders at the Bellevue Botanical Garden. By…

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Late winter in the NPA Borders: the colorful stems of willows and dogwoods underplanted with yellow narcissus and deeply colored garden hybrid hellebores (Helleborus 5 hybridus). Photographs by Lynne Harrison - See more at: http://www.pacifichorticulture.org/articles/lessons-from-the-npa-borders-hellebores/#sthash.x3zvbqgb.dpuf

Late winter in the NPA Borders: the colorful stems of willows and dogwoods underplanted with yellow narcissus and deeply colored garden hybrid hellebores (Helleborus 5 hybridus). Photographs by Lynne Harrison

More than fifteen years since its inception, the extensive Borders at the Bellevue Botanical Garden, designed, installed, and maintained by volunteers from the Northwest Perennial Alliance, have matured into one of the region’s most exciting horticultural landmarks, with something to offer the visitor in any season. Midwinter can be quiet, except for the colored twigs of willows and dogwoods, but late winter and early spring burst forth with an abundance of hellebores. In this first in an occasional series of articles on what the volunteers have learned from their years in the Borders, one of the early designers and a continuing volunteer leader reports on their successes with garden hybrid hellebores.

Among the great successes in the Borders at the Bellevue Botanical Garden have been the garden hybrid hellebores (Helleborus x hybridus). Of all the species we have tried, these do best for us in beds where the soil is heavy, the exposure is open shade with the summer sun filtered through deciduous shrubs, trees, and shrub roses, and supplemental water is distributed through a drip or leaky-pipe irrigation system.

We have used masses of the garden hybrids to provide an early spring show amongst soon to emerge perennials, such as daylilies (Hemerocallis), Siberian iris (Iris sibirica), and geraniums. We mix the hellebores with early bloomers like Omphalodes cappadocia, O. verna, and a wide selection of the cultivars and newly introduced species of Epimedium. The overstory of shrubs includes viburnums, red-twig dogwood (Cornus stolonifera), Paeonia lutea, Japanese barberry cultivars (Berberis thunbergii), and shrub roses, some trained on iron supports and others freestanding (Rosa glauca and R. californica ‘Plena’).

To broaden the show at hellebore time, we depend upon masses of buttercups (Ranunculus ficaria), putting R. ficaria ‘Randall’s White’ near the dark hellebores, R. ficaria ‘Late Cream’ close to the lawn near the Visitor’s Center, and R. ficaria ‘Brazen Hussey’, with its dark leaves and brilliant yellow flowers, in several locations, most notably paired with black mondo grass (Ophiopogon planiscapus ‘Nigrescens’).

When the Northwest Perennial Alliance began planning the Borders, we had available to us a group of dark and slaty hybrid hellebores that Kevin Nicolay had bred and raised from seed. We also had a great many plants raised by Charles Price, including good darks (the plum purple ones), reds (a good maroon red), and some pinks. Additionally, we were able to choose a few dark selections from Charles’ breeding work that had been grown by Phillip Curtis Farms (no longer in business). Because of this initial bounty, we now have a fine selection of dark maroons and good rich reds, although none have the dark nectaries that are a current focus of breeding.

As the shrub spine down the center of the Main Border has matured, we’ve added more pink and many more white hellebores in the understory. The design intent here is to showcase a drift of white hellebores easily visible from the Visitor’s Center and its patio in February and March, which will precede the bloom of thousands of Narcissus ‘Pipit’ planted in front of them.

Our hybrid hellebore population ranges from pure ice-white through pink in the southern end, then progresses to red and on to the extreme dark colors at the northern end of the Main Border. The newer, dark-flowered selections have been planted in the northern end of the West Border. If any rogues appear outside this color scheme, we remove them and pot them up for our plant sales.

Recently, we have been planting some appealing double-flowered hybrids from Northwest Garden Nursery in Eugene, Oregon. Fortunately, the NPA Borders are large enough that we can find corners and isolated areas to feature them. The double maroon ones are on the backside of the Double Border with Primula ‘Guinevere’ and P. ‘Miss Indigo’, juxtaposed against the light mottled bark of crape myrtle (Lagerstroemia indica).

Hybrid hellebores (Helleborus 5 hybridus) at the base of a rose, which will provide shade during the summer; last year’s hellebore leaves have been trimmed tidily and plants mulched with granite chips - See more at: http://www.pacifichorticulture.org/articles/lessons-from-the-npa-borders-hellebores/#sthash.x3zvbqgb.dpuf

Hybrid hellebores (Helleborus 5 hybridus) at the base of a rose, which will provide shade during the summer; last year’s hellebore leaves have been trimmed tidily and plants mulched with granite chips

Tips on Cultivation

Most clumps are allowed to grow as large as they wish; we remove them only if they are diseased or have a reduction in their flowering. Our soil is heavy clay, and the hellebores form large, densely rooted clumps that are difficult to handle. After lifting a clump, we first wash it to remove some of the excess soil; then, we divide it by either pulling segments apart with spading forks or unceremoniously hacking the clump into quarters with an axe. Most of the plants we produce are saved for our plant sales or given to volunteers. There are usually big divisions left over from the propagation workshops or seedlings potted up from the Borders. Some of our members bring in large clumps they no longer need or want, thus providing more plants for workshop participants.

Seedlings are potted up into four-inch pots at the first appearance of true leaves and are held for one year. We choose only those found under our best mother plants for this. Two and three-year-olds are removed from the garden and potted in gallon cans, often held for eighteen months so that we can sell them in flower. All hellebore potting is done in March, during classes and workshops on the second Saturday and second Sunday of the month.

We use limestone (or marble) chips as mulch around our hellebores and herbaceous peonies to control botrytis, a disease that blackens the foliage and disfigures the flowers. The chips (used for terrazzo floors) shed molecules and constantly reduce the acidity in the mulch, which makes the over-wintering of botrytis spores less likely. The chips do not change the pH of the soil, however, so acid soils may still need an application of lime (dolomite) to bring the pH at least to neutral.

Certain species of aphids love hellebores, feeding on both flowers and foliage. They have become a problem during seed collection: they make drying the seeds messy and can cause a rash on volunteers’ arms. The aphids’ effect on the plants is mostly cosmetic, though they can be vectors for disease. They can be washed off the foliage with a good stream of water, especially on the undersides of the leaves.

To reduce disease problems, and show off the flowers better, we remove all the foliage towards the end of February as the new shoots are appearing. The stems must be cut close to the ground so there will be no stubs visible to spoil the presentation of the flowers. This procedure really showcases the flowers but it also leaves them a bit more vulnerable to frost.

A deep maroon garden hybrid hellebore (Helleborus 5 hybridus) - See more at: http://www.pacifichorticulture.org/articles/lessons-from-the-npa-borders-hellebores/#sthash.x3zvbqgb.dpuf

A deep maroon garden hybrid hellebore (Helleborus 5 hybridus)

NPA Hellebore Open House

March 4, 2007, 11 am to 3 pm
Bellevue Botanical Garden
12001 Main Street, Bellevue, WA
www.northwestperennialalliance.org

With all the hellebores in the garden, Elfi Rahr (Helleborus Woodland Garden) was the first to suggest that we have an “open house” during hellebore season, along with a plant sale at the Bellevue Botanical Garden. The Hellebore Open House has become an established, and highly awaited, event in the Northwest Perennial Alliance annual calendar. With ten vendors bringing hellebores of all types, along with spring bloomers like primula, narcissus, tulips, and other spring bulbs, there are always lots of surprises. The NPA is also a vendor featuring our signature plants: seedlings of the dark and white hybrid hellebores, Ranunculus ficaria ‘Brazen Hussey’, Omphalodes, Iris foetidissima ‘Variegata’, Milium effusum ‘Aureum’, and Pulmonaria angustifolia.

We also stage a hellebore display inside the Bellevue Botanical Garden Visitor Center, with cut stems of every color and flower variation that we can find. Our members bring in flowers from their gardens, cut stems from the Borders, and still more flowers from Elfi Rahr’s garden, displaying as many species and hybrid selections as possible. Last year, we added a display of narcissus cultivars in bloom in the Borders.

We also collect seed from almost all of the hellebores in the Borders, with some packaged as a mix and some from specific plants (although still open pollinated). The NPA Seed Exchange is now accessible on our website; we try to have the fresh seed ready by mid-July. Look for ‘Kevin’s Best Slate’, ‘Kevin’s Best Dark’, ‘PC Farms Dark’, ‘Our Best Reds’, ‘Pure White’, ‘Star-shaped White’, and ‘Mixed Pinks’. Not all seed is available every year; we need more bumble bees!