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Postharvest Handling of Six Field-grown Cut Flowers; Astilbe, Gladiolus, Helianthus, Liatris, Lilium, Zinnia

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Helianthus
Liatris
Cut flower

Production of field-grown cut flowers has become quite popular in recent years. The variety of flowers grown has also increased dramatically. While production of high-quality flowers is important, it is equally critical to handle the flowers properly after they are harvested from the field. There are reports that improper postharvest handling accounts to 20 to 30% of cut-flower loss during marketing. In the factsheet titled Sugar and Acidity in Preservative Solutions for Field Grown Cut Flowers, I reported on some basic postharvest treatments that should be used on all field-grown cut flowers. In this article, I will discuss specific treatments that have been reported to improve greatly the postharvest quality of six field-grown cut flowers.

Astilbes

Harvest when one-half to three-quarters of the flowers are open. The uppermost buds should be swollen and showing color. Place cut stems immediately in an acidified, 130o F solution. Leaving the stems dry even for a few hours will reduce the vase life of the cut stems.

Flowers are sensitive to ethylene. Pretreatment with EthylBloc (an antiethylene compound) is recommended.

If flowers are not sold immediately, store them in a 33-40o F cooler for up to 7 to 10 days in a solution containing a bactericide. Polyethylene sleeves are better than paper sleeves.

If flowers are to be shipped a long distance and will be stored dry, a treatment with 100 ppm of Triton X-100 surfactant (a non-ionic detergent) prior to the cold storage significantly reduces the wilting of the flowers and leaves. Treatment with other surfactants, Tween 20 or Tween 80, at 0.1 ppm (concentration that can restore turgidity) results in visible leaf damage and abscission and should not be used.

Use of preservatives in the vase solution will increase the vase life of cut stems.

Gladiolus

Harvest when 1 - 5 flowers on the spike are showing color. Place in a solution containing a bacteriocide, citiric acid, and 4 to 6% sugar.

In recent years, researchers have shown that gladiolus flowers are insensitive to ethylene even when exposed to 1 ppm of ethylene. However, treatment with 1 mM STS (an anti-ethylene compound) for 2 hours improves the opening of the small buds and consequently the postharvest life of the cut stems. The article (by Mayak, Bravdo, Gvilli, and Halevy, 1973) demonstrates that the small buds at the tip of the spike often abort due to carbohydrate depletion, which leads to increased ethylene biosynthesis. By pretreating cut gladiolus with STS, small buds will develop as if the stems were placed in a preservative solution containing sugars. In fact, the authors showed that the opening of spikes is the same for stems pulsed with STS and then placed in DI water as for those placed in a 1 % sugar solution but were not pulsed with STS. While STS is no longer available for use, the new anti-ethylene compound (EthylBloc) would serve the same purpose. A 5-hour treatment of the EthylBloc at the recommended rate would assure proper development of the small buds, and thus better-quality stems for your customers to enjoy.

Alternatively, gladiolus stems can be placed in a 20% sugar solution overnight (about 20 hrs) and then transferred to solutions that do not contain sugar. This treatment results in a greater number of opened flowers and larger flowers, thus longer vase life for the cut stems.

Helianthus (Sunflower)

Without doubt, sunflowers are one of the most popular cut flowers during the past few years. To ensure maximum postharvest life, harvest when the flowers are almost completely open.

Store wet, preferably in a 36 - 41o F cooler. When stored dry for up to 24 hrs, irreversible wilting of leaves may occur. Too much Triton (higher concentrations or longer treatment time), however, can damage the leaves. Triton works by improving hydration before cold storage, reducing water loss during cold storage, and improving post-storage hydration (30% greater) after dry storage. Pretreatment with Triton will significantly improve vase life, especially on those flowers that will be cold-stored for 3 or more days. Another surfactant, Tween 20, works as well (Alan Stevens personal communication).

Liatris (Gayfeather)

Harvest when 3 to 4 flowers have opened and then place in a 5% sugar solution for 24-72 hrs. Alternatively, place cut stems in a preservative solution containing 2.5 to 5% sugar to increase the opening of the buds on the spike, and consequently to extend the vase life of the cut stems.

If preservative solution is not used, then the inflorescence should be harvested with at least one-half of the flowers opened. Stems can be stored in a 32-35o F cooler for up to a week.

Lilium sp. (Oriental and Asiatic lilies)

Harvest when the first flower is fully colored, but not open. If flowers are to be stored, place them in water in a 35-41o F cooler.

It is recommended that cut lilies not be cold stored. Cold storage (4 or more days) will induce rapid development of postharvest leaf yellowing. Spraying leaves with a solution containing 25 ppm of BA and 25 ppm of GA4+7 can prevents the development of leaf yellowing. These growth-regulator solutions can be sprayed before cold storage (in the greenhouse or in the handling room) or after the cold storage (in a retail store); however, they are currently not registered for use on lilies.

Zinnias

Cut Zinnias have remained popular cut flowers for many years. Flowers should be harvested when fully mature and the pollen is beginning to form.

A warm, acidic solution improves hydration, especially on stems that are harvested in the summer. Cut stems should be placed in a cool, shaded area as soon as possible. They can be stored wet in a 36-38o F cooler for 5 days without deterioration of quality.

Preservatives containing 1% sugar and a biocide significantly improve postharvest quality and life. Higher concentrations of sugar will damage leaves and petals and should be avoided.

Flowers harvested in the summer have a longer vase life than those harvested in the fall. To ensure satisfactory vase life, a preservative solution containing sugars is absolutely necessary for flowers that are harvested at the end of the growing season.

Literature cited

  • Jones, R.B., M. Serek, and M.S. Reid. 1993. Pulsing with Triton X-100 improves hydration and vase life of cut sunflowers (Helianthus annuus L.). HortScience 28:1178-1179.
  • Kalkman E.Ch. 1986. Post-harvest treatment of Astilbe Hybr. Acta Hort. 181:389-392.
  • Mayak, S., B. Bravdo, A. Gvilli, and A.H. Halevy. 1973. Improvement of opening of cut gladioli flowers by pretreatment with high sugar concentrations. Scientia Hort. 1:357-365.
  • Nowak, J. and R.M. Rudnicki. 1990. Postharvest handling and storage of cut flowers, florist greens, and potted plants. Timber Press, Portland, Oregon.
  • Serek M. , R.B. Jones, and M.S. Reid. 1994. Role of ethylene in opening and senescence of Gladiolus sp. flowers. J. Amer. Soc. Hort. Sci. 119:1014-1019.
  • Stimart, D.P. and D.J. Brown. 1982. Regulation of postharvest flower senescence in Zinnia elegans Jacq. Scientia Hort. 17:391-396.
  • Van Doorn W.G., R.R.J. Perik, and P.J.M. Belde. 1993. Effects of surfactants on the longevity of dry-stored cut flowering stems of rose, Bouvardia, and Astilbe. Postharvest Bio. Tech. 3:69-76.
Prepared by:
Dr. Susan S. Han, Stockbridge School of Agriculture
University of Massachusetts, Amherst

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