Tiptoeing Through the Tiarella

• By Pat Chadwick
• /
• February 2017-Vol.3 No.2
• /
• 4 Comments

When I think of plantings for shade gardens, I invariably think of Tiarella cordifolia, or foamflower.   I love its delicate foliage and airy clouds of dainty flowers.  I love how it lights up the various nooks and crannies of a woodland garden.  I love how it looks fresh and inviting regardless of the summer heat and humidity.  Sadly, my current ornamental garden is too sunny for this sweet plant.  So I must enjoy it vicariously when I spot it growing in more suitable settings elsewhere.

A shade-loving perennial, Tiarella is native throughout the eastern United States and Canada and hardy in USDA zones 5 to 9.  Its botanical name means little crown, a reference to the shape of its seeds.  Its common name comes from the airy, foamy-looking racemes of tiny white to pink flowers held above the foliage on thin, wispy stems.

Close Up of Tiarella cordifolia (Foam Flower) blossom

Relatively low growing, Tiarella averages about 6 to 12 inches in height and 12 inches in width.  In the wild, it appears as a low-growing, mounding or spreading evergreen perennial on the banks of streams and in moist woodland conditions.  In the cultivated ornamental garden, the evergreen foliage lends an interesting display of texture and color throughout the year.  Light to medium green during the growing season, the foliage takes on a bronze or purple hue in the winter.  Depending on the variety, the leaves are either mildly or deeply lobed with uneven toothed edges.  While the foliage is interesting in its own right, the flowers are the icing on the cake. The floral show generally lasts for several weeks in spring before fading.  Even the faded flowers can add interest to the landscape.

Two Tiarella varieties are native to the east coast of North America.  Both were honored with the Royal Horticultural Society’s Award of Garden Merit in 1993:

• Tiarella cordifolia var. cordifolia
  

  Tiarella cordifolia

  – Known by the common names of Allegheny foamflower and heart-leaved foamflower, it has dense clumps of heart-shaped leaves that have three to five mild indentations, toothed edges, and often display dark burgundy or maroon veining or patches. The flowers are white to pale pink.  This species is characterized by aboveground runners, called stolons, which allow the plant to spread as a ground cover.

• Tiarella cordifolia var. collina –
  

  Tiarella wherryi

  Also called T. wherryi, or Wherry’s foamflower, this species is taller with foliage that is more deeply lobed, resembling the leaves of maple, fig, or oak trees. A well-behaved clump-forming variety, it will not outgrow its assigned space in the garden and is therefore a better choice if space is limited.  This variety typically produces more racemes of flowers than the runner type.

Another native species, Tiarella trifoliata, which is also called western foamflower or three-leaf foamflower, is native to the Pacific coast.  Somewhat taller than the east coast species, it ranges in height from 9 to 20 inches.   It is less tolerant of heat and humidity than the eastern species and therefore not suitable for east coast gardens.

Tiarella trifoliata

Tiarella polyphylla, or Asian foamflower, is a related species that is native to China, Japan and the Himalayas.  Asian foamflower looks similar to our native Allegheny foamflower, but it is not as heat and humidity tolerant.   It is a clump-forming species that spreads slowly.

Thanks to the interest and attention that plant hybridizers have given Tiarella, many hybrids with interesting leaf colors and shapes have been created by crossbreeding the native eastern species with other related species.

TIARELLA, HEUCHERA, HEUCHERELLA – WHAT’S THE DIFFERENCE?

In addition to cross-hybridization among Tiarella species, hybridizers have created a number of cross-hybrids with Heuchera, commonly known as coral bells.  And therein lies much confusion.   Botanically, Tiarella and Heuchera are closely allied since they both belong to the Saxifragaceae genus.  In general, they enjoy similar growing conditions although Tiarella prefers a moister environment and can tolerate more shade than Heuchera.  The two species form low-growing mats of foliage and they both have tiny flowers that appear on wands held above the foliage.  Heucherella, the intergeneric cross between the two species, combines the best characteristics of both plants in terms of flowers and foliage.  The common name for this cross between foamflower and coral bells is “Foamy Bells.”  Heucherella tends to have deeply divided foliage that is more brightly colored and patterned with blotches and contrasting veining than either parent.  The flower stems also tend to be shorter than those of either parent.

Tiarella Cordifolia (Foamflower)

Various Heuchera Selections

Heucherella ‘Stoplight’

CULTURAL REQUIREMENTS OF TIARELLA

Tiarella does best in moderate to full shade with morning sun only.  It prefers rich, organic soil with a pH of 6.2 to 6.5, and evenly moist, but not soggy, growing conditions.  This plant does not like wet feet.  Established plants are somewhat tolerant of drought conditions, but they will spread more slowly than when given moist growing conditions.  If planted in dry shade, improve the soil by incorporating plenty of organic matter.  To maintain a high humus level, mulch yearly with chopped leaves or compost in late fall or early spring.   While organic matter is recommended to lighten clay soil, fertilizer is not normally needed for this plant.

TIARELLA PESTS AND DISEASES

Other than occasional issues with slugs and snails, Tiarella species are generally free of insect pests and diseases. The leaves are astringent, which means that deer and rabbits generally don’t eat them unless they are extremely hungry and no other suitable food sources are available.

While Tiarella enjoys moist soil, it can suffer from Phytophthora root rot if the soil does not drain well.

TIARELLA PROPAGATION METHODS

Commercial plant nurseries often use tissue culture to grow new Tiarella plants.  But the homeowner may start new plants by planting seeds, rooting runners, or dividing clumps.   Seeds should be shallowly sown in early spring or in autumn and protected in a cold frame.  The fresher the seed, the better. They tend to sprout quickly although the seedlings may be slow growing.   Aboveground runners (stolons), may be dug up and rooted any time during the growing season.  Plant them about one to two feet apart and they will eventually fill in the spaces between plants.  Clumps may be divided late in the fall.

USES FOR TIARELLA IN THE LANDSCAPE

Tiarella is a versatile plant that can be used to great effect in the landscape.  One of the most intriguing uses for it that I’ve ever seen was many years ago in a tiny postage stamp-size garden in Georgetown, a historic neighborhood of Washington, D.C.  The immaculate little garden was planted with just two species, Tiarella and tulips, both of which showed brilliantly against a backdrop of perfectly clipped dark green boxwoods.  The Tiarella clumps, which were planted in a grid formation, had lime green foliage with burgundy veining.  Taller, soft pink ‘Angelique’ tulips emerged at precise points within the composition and in perfect harmony with the shorter Tiarella.   The interplay of pink, burgundy and lime green against the dark green of the boxwoods was absolutely stunning.

Such a formal treatment is unusual for what is first and foremost a wildflower.  Tiarella is more likely to be used in an informal garden setting.  For example:

• Use the spreading (stoloniferous) type as a ground cover or mass planting beneath deciduous trees and shrubs in a woodland setting.
• In the shady mixed border, intersperse either singly or in small groupings among other herbaceous shade-loving perennials such as hostas, ferns, coral bells (Heuchera), Epimedium, dwarf crested iris (Iris cristata), woodland phlox (Phlox divaricata), Corydalis, and Solomon’s seal (Polygonatum).
• Mix with other plants to help control erosion of soil along the banks of streams, thus improving water quality.
• Incorporate with other moisture-loving plantings in a shady to partially shady rain garden.
• Considered a “must-have” native plant in a wildflower setting, use it with other shade-loving wildflowers to provide nectar to bees, flies, and other pollinators in spring.
• Showcase as a key component of a shade garden container or urn.
• Nestle among stones in a shady rock garden. The delicate little flowers contrast nicely with the stones, softening the overall effect.  For a garden with boulders, use a larger, denser clumping cultivar such as T. wherryi ‘Oakleaf’ to provide a better balance with the scale of the boulders.

SOURCES

Herbaceous Perennial Plants, A Treatise on their Identification, Culture, and Garden Attributes, Third Edition (Armitage, Allan M., 2008)

Native Plants of the Southeast (Mellichamp, Larry, 2014).

Perennials, The Gardener’s Reference (Carter, Susan; Becker, Carrie; and Lilly, Bob; 2007)

Plant Propagation (The American Horticultural Society; Toogood, Alan, Editor-in-Chief; 1999)

Taylor’s 50 Best Perennials for Shade (Tannenbaum, Frances, Series Editor, 1999)

Albemarle County Recommended Native Plants Database, albemarle.org/nativePlants

United States Department of Agriculture Plants Database, plants.usda.gov

Virginia Cooperative Extension Publication 426-043, Rain Garden Plants