Using Coralbells as Cut Flowers

Heuchera, commonly known as coralbells, is a popular garden perennial. There are many different species available on the market, all of which are native to North America. The slender scapes bear open clusters of flower buds of different colors, ranging from white, to greenish white, to pink, to crimson, to scarlet, and to red. Opening of the flowers buds typically starts from the base of each branch and continues toward the tip resulting in an attractive inflorescence that could be used as a filler in floral arrangement.

Coralbells can be forced to flower in the greenhouse year round by placing mature plants (plants that are 10 month from seeding) in a 40 F cooler for 10 to 12 weeks. Following the cold treatment, plants should be moved to the greenhouse for forcing. The first buds on the inflorescence open 6 to 9 weeks after transfer to a greenhouse with 62 F night temperature. The forcing time varies depending on cultivar, environmental conditions, and length of the vernalization treatment. The size of the plants at the time of the cold treatment and the duration of the cold treatment will determine the number of inflorescences produced by each plant.

At the University of Massachusetts, we evaluated the postharvest quality of coralbells when used as cut flowers. Plants of two cultivars, 'Splendens' and 'Bressingham', were started from seed and the cold treatment was applied to plants as previously described. In this study, there was an average of 57 and 86 buds per inflorescence for 'Splendens' and 'Bressingham', respectively, which were harvested from the greenhouse at the predetermined stage of development. They were then placed individually in test tubes containing preservative solutions or water (for comparison) and the postharvest quality of the cut stems was evaluated in a 70 F interior room illuminated for 12 hours a day with a cool-white fluorescent lamp. The inflorescence were examined daily and the vase life of each inflorescence was considered terminated when the number of senescing flowers on the inflorescence exceeded that of the open flowers. We investigated several factors that affect postharvest quality of cut flowers, including the optimum harvesting stage, the concentration of sucrose in the preservative, and the effects of ethylene.

Harvesting stage and preservatives

Like many other cut flowers, the harvesting stage of the inflorescence (flower) determines the vase life of the cut stems. In coralbells, all flower buds on inflorescences with more than 70% of the buds open at harvest continued to develop when placed in water. The vase life of the inflorescence, however, was only 4 to 6 days. Inflorescences that were harvested at an earlier stage (1 to 2 buds opened on each axillary branch), however, had a vase life of 16 days for 'Splendens' and 9 days for 'Bressingham' if proper postharvest treatments were provided. Buds on these inflorescences did not open or develop and open flowers abscised rapidly if the cut stems were placed in water, resulting in a vase life (defined previously) of approximately 4 days. As in the case of many other flowers, continuous development of immature buds requires a supply of carbohydrates which is limited in the leafless, slender scapes. The vase life of coralbells harvested at a young stage was significantly improved when the cut stems were placed in preservative solutions containing a small amount of sucrose and a biocide. Our studies revealed that 0.5 to 1% of sucrose in the solution (1-2 teaspoons of sugar per quart of water) was sufficient for the opening of all flower buds and the quality as well as the vase life of the cut inflorescences was significantly improved. Too much sugar (>2%), however, was detrimental to coralbells and resulted in collapsed stems.

Most of the commercially available preservatives, when properly mixed, contain 1 to 2% sugars. Therefore, when commercial preservatives are used, make sure to make up a quarter to full strength of solution. A small-scale experiment, using a few cut stems, should be conducted by placing the cut inflorescences in either quarter, half, or full strength solution of the preservative, and compare the postharvest quality of the flowers to those place in water.

Ethylene and STS

During the early phase of our investigation, we learned that a large number of flower buds abscised a few days after placing the cut stems in the interior environment. This phenomenon suggested that ethylene might be involved in the abscission and that pretreatment with silver thiosulfate (STS) might be necessary. Silver thiosulfate is available commercially to treat flowers that are sensitive to ethylene. In fact, all of the cut carnations grown today are treated with STS to ensure that the flowers have a satisfactory vase life. We treated cut coralbells with 4mM (standard concentration of STS used in treating cut flowers) for 4 hours and found that the treatment completely prevented the abscission of buds. Buds on the STS-treated inflorescences, however, did not develop and shrivelled if the inflorescences were placed in a solution with no sugar. In contrast, when placed in preservative solution containing 0.5 to 1% of sugars (and a biocide), all flower buds opened and the vase life of the stems was significantly improved. In addition, we also demonstrated that coralbells are very sensitive to exogenous ethylene. An exposure to ethylene caused all of the open flowers to senesce and the buds to abscise.

In conclusion, cut coralbells which contain open clusters of flower buds of many different colors can be used as filler flowers in floral arrangements. The minimum harvesting stage (defined as the stage at which buds on the stems will continue to develop with proper postharvest treatment, resulting in a satisfactory vase life) of coralbells is when 2-3% of the flower buds are opened (1 open flower bud per axillary branch). When harvested at this stage, the inflorescence should be treated with STS solution for 4 hours and then placed in a preservative solution containing 0.5 to 1% sugars and a biocide. Without the preservative, the large number of immature buds on the scape will not develop. On the other hand, inflorescences can be harvested at a later stage when most of the buds are open. At this stage, inflorescence should be treated with STS but the use of sugars in the vase solution is optional. Adding sugars to the vase solution will improve the quality of the inflorescence by enhancing the color of the petals and increasing the number and size of flowers.

References

  • Han, S.S. 1984. Factors affecting flowering of selected herbaceous perennials. MS Thesis., Univ. of Missouri, Columbia, Mo.
  • Iversen, R.R. 1990. Perennial pickings: 5 garden favorites cut from the greenhouse. GrowerTalks 53:38-42.
Prepared by:
Dr. Susan S. Han, Stockbridge School of Agriculture
University of Massachusetts, Amherst

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