In recent years, heuchera, tiarella and heucherella have become incredibly popular in landscapes. All of them are closely related and belong to the Saxifragaeae family. Commonly referred to as foamy bells, heucherella cultivars are intergeneric hybrids between the heuchera and tiarella genera. Most breeding occurs between two plants belonging to the same genus and species; however, hybrids derived from two different genera are fairly rare, which adds to the uniqueness of heucherella cultivars.
Heucherella ‘Burnished Bronze’ is a great intergeneric hybrid brought to market by Terra Nova Nurseries. It is a clump-forming perennial that produces a compact, 8- to 10-inch-tall mound of large, deeply cut, glossy, burnished-bronze leaves. The star-shaped, tawny-beige to pink flowers appear on 18-inch, branched scapes from late spring to mid summer. Additional sporadic flowering often occurs throughout the growing season, particularly in autumn.
‘Burnished Bronze’ is a patented variety and is currently only propagated by tissue culture; self-propagation is prohibited at this time. Most growers will purchase cultivars from tissue culture as 72-cell or larger-sized plugs from licensed propagators.
For the best leaf coloration, produce ‘Burnished Bronze’ in partial shade. Production in locations with full sun will cause the leaves’ color intensity to fade. Locations with full shade will also greatly reduce growth rate and landscape performance. If plants must be produced in full sun, it is very important to give them consistent moisture levels. Regardless of light intensity, leaf scorch will usually occur when soils are allowed to dry out.
Like most heucherella cultivars, ‘Burnished Bronze’ performs throughout USDA Hardiness Zones 4-9. Foamy bells perform better in northern locations than in southern locations; plant performance and longevity are greatly reduced as the average temperatures increase. ‘Burnished Bronze’ is versatile and often grown commercially for mixed containers or used in borders, rock gardens and mass plantings.
‘Burnished Bronze’ is commonly grown in container sizes ranging from 1 qt. to 1 gal. Most commercially available peat or bark-based growing mixes work well, provided there is adequate drainage. It is important to plant plugs so the top of the media is level with the potting media of the new container. Planting heucherella too deeply will most likely lead to poor plant establishment and possibly even plant mortality caused from crown rots.
The root zone should be kept uniformly moist until roots reach the outside of the root ball. Heucherella require an average amount of irrigation, as they do not tolerate really wet conditions or overly dry conditions. Under high light intensities, marginal leaf burn may occur if the plants become water stressed. When irrigation is necessary, water plants thoroughly, and then allow the soil to dry slightly between waterings.
Foamy bells are considered light to moderate feeders and require modest fertility levels. Maintain the pH between 5.5 and 6.5. Growers using water-soluble fertilizers should either apply 150- to 200-ppm nitrogen as needed or feed with a constant liquid fertilization program using rates of 50- to 100-ppm nitrogen with every irrigation.
Controlled-release fertilizers are commonly used to produce containerized heucherella. Growers commonly apply time-release fertilizers as a top dress onto the media surface using the medium rate or incorporate them into the growing medium prior to planting at a rate equivalent to 1 lb. of elemental nitrogen per yard of growing medium.
Height control is seldom necessary to control the leaf growth unless plants are grown at high densities. However, reducing the height of flowering stems or panicles is often beneficial for growers who ship plants in bloom. I have found applications of Sumagic (Valent USA Corp.) at 5 ppm (northern rate) to be effective at controlling both plant height and flower stem elongation. Apply growth regulators as the panicles are just beginning to elongate above the foliage. Two applications applied seven days apart will provide an adequate reduction of the flowering stalk without altering the overall appearance of the plant.
Occasionally, aphids and spider mites may appear and cause minimal amounts of crop injury. These insect pests do not require preventative control strategies. Growers should have routine scouting programs to detect the presence of insects early and determine if and when control strategies are necessary.
When the proper environmental and cultural factors are provided, heucherella can generally be produced without occurrence of plant pathogens. Root and crown rots caused from Phytopthora, Phythium and Rhizoctonia are the primary diseases growers should be concerned about. They are most susceptible to these pathogens when overwatered or grown under cool conditions, such as going into or coming out of winter dormancy. Botrytis is another disease that could become problematic. Botrytis, like Rhizoctonia, often occurs around the overwintering process but is also likely to occur under dense plant canopies. With good watering practices and adequate air circulation, the occurrence of most diseases can almost be negated.
‘Burnished Bronze’ is easy to produce as a foliage plant. When transplanting from 72-cell plugs, foamy bells grown at 65° F typically take six weeks to finish 1-gal. pots in the summer or nine weeks during the winter months. Growers wishing to produce blooming plants need to understand and follow the guidelines discussed below.
Heucherella have an obligate cold requirement in order to flower. It is recommended to cool (vernalize) small containers of foamy bells for a minimum of nine weeks at 35-44° F. After the cold requirement is achieved, heucherella can be grown at any day length, as they are day-neutral plants. The length of the photoperiod does not affect the time to flower or the number of blooms produced.
The time to bloom after vernalization is a function of temperature. ‘Burnished Bronze’ grown at 63° F will take approximately seven weeks to reach flowering, while plants grown at 68° F will flower in five weeks. Producing a crop at cooler temperatures increases the time to flower but will improve the overall quality characteristics of the plants, such as the color intensity of the foliage and flowers.
To obtain full, flowering plants for spring sales, it is beneficial to start plants during late summer of the previous season. I recommend transplanting plugs into the desired container during mid to late August, bulking them up before winter, overwintering and forcing them to bloom in early spring.
Heucherella ‘Burnished Bronze’ is brought to the industry by Terra Nova Nurseries (www.terranovanurseries.com ) from Tigard, Ore. It is available to growers most commonly as finished plugs from Terra Nova or other reputable plug producers throughout the country.