Years ago when life and gardens were simpler, there was a dependable plant often found growing in partially shaded perennial borders. It had a pleasant mounding form, green, lobed leaves, and sprays of tiny bell-shaped flowers held high on slender stems. The flowers were coral, and the plant was called coral bells.
Decades and dozens of hybrids later, Heuchera spp. is as well known for the striking colors of its foliage as it is for its long lasting flowers. Thanks in part to the aggressive breeding, tissue culture propagation, and plant introduction program of Dan Heims' Terra Nova Nurseries in Oregon, there are new coral bells cultivars offered annually. The once green-only foliage is now bronze, copper, olive, or purple with silvery tracings etched on the upper leaf surfaces. The underside of those leaves is often solid burgundy. Lobed, wavy, or even ruffled leaves can emerge one color, only to mature to another shade. Flowers range from greenish white to magenta red. Imagine the possibilities with names like 'Amber Waves', 'Cathedral Windows', 'Champagne Bubbles', Plum Pudding', and 'Amethyst Myst'. But, no matter how tempting the name, can this plant perform in Chicago gardens?
Richard Hawke, manager of Plant Evaluation Programs at the Chicago Botanic Garden, conducted a four-year study of more than 60 different coral bells, available in Plant Evaluation Notes #21. The plants were evaluated in partial shade in clay soil enriched with organic matter to suppress weeds and retain moisture. Coral bells prefer an even, never soggy, supply of moisture in rich, organic, well-drained soil. If planted in full sun, extra moisture must be supplied to prevent drying out. Since they are shallow rooted and prone to frost heaving, add 2 to 3 inches of mulch once the ground has frozen as extra winter protection. Some plants will become large and woody over time and will benefit from spring division to renew their mounding habit.
Mr. Hawke's evaluation comes at a time when garden centers are flooded with new plants. As he notes, "A good garden center plant is not necessarily a good garden plant." There can be losses with coral bells; and as the new introductions are relatively expensive, it makes sense to know which ones are more likely to become lasting members of your garden. Plant hardiness is not as much a factor of the cold as it is a result of the soil. "We pay so much attention to weather in this part of the country. Most of the time, that's not the real issue. It's the soil we should focus on," he commented.
Mr. Hawke offers a glimpse of the top five performers:
1. Heuchera 'Molly Bush' grows 30 inches tall (including flower stems) and features dark purple foliage that turns green as the plant matures. Greenish white flowers bloom from mid-July to early October, covering 80 percent of the plant. This is a darker improvement over the very popular 'Palace Purple'.
Second place is shared by two plants:
2. Heuchera sanguinea 'White Cloud' is shorter at 26 inches, with light green foliage and white flowers that appear earlier in June through late July, covering 80 percent of the plant.
2. Heuchera 'Montrose Ruby' grows to 3 feet with purple green leaves with a silver cast, and white flowers that bloom from mid-June to early August, covering 50 percent of the plant.
3. Heuchera americana var. diversifolia 'Bressingham Bronze' grows to 26 inches with dark bronze green leaves and white flowers that bloom from early August to mid-October, covering 50 percent of the plant.
Fourth place is shared by three plants:
4. Heuchera 'Cappuchino' is a 30-inch light bronze plant with pink flowers that appear in early June to early August, covering 50 percent of the plant.
4. Heuchera 'Red Prince' grows to 26 inches with green foliage and red flowers that bloom from early June to mid-August, covering 90 percent of the plant. Red-flowered coral bells are known to attract hummingbirds.
4. Heuchera micrantha var. diversifolia 'Palace Purple' is one of the most popular purple-foliaged coral bells in gardens today. It grows to 32 inches with bronze purple leaves and the greenish white flowers bloom from mid-July to early October, covering 70 percent of the plant.
5. Heuchera 'Coral Cloud' at 28 inches features light green leaves with silver overtones and purple pink flowers that bloom from early June to late July, covering 50 percent of the plant.