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Ethylene Effects and Control Measures

Historical considerations: In 1609, a Belgian chemist discovered that gases released from heated coal could produce a flame. Nearly 200 years passed before a German engineer constructed a manufacturing facility to produce gas to light homes, businesses and streets. Commercial production and use of illuminating, coal, or manufactured gas became routine in industrialized countries during the 1800s.

In 1864, a report showed that shade trees located near leaking underground illuminating gas pipes that serviced street lamps defoliated. But it wasn't until 1901 that ethylene was identified as the active component of illuminating gas causing plant growth disorders. What led to the ethylene discovery was the observation that pea seedlings grew horizontally in greenhouses contaminated with this gas, but grew upright when fresh air was introduced into the same greenhouses.

Effects on plants/flowers (general): Countless articles have documented how this gas became known as the death hormone of plants or, as many believe, the major post-harvest enemy of the floral industry. Some negative plant responses to ethylene and examples of plant species affected include:

  • Premature loss of foliage (ficus, azalea, rose, citrus)
  • Premature loss of flowers (geranium, snapdragon, impatiens)
  • Premature loss of fruit (holly, pepper, citrus)
  • Premature flower death (carnation, kalanchoe, cattleya)
  • Translucent petals (alstroemeria, gypsophila)
  • Adventitious stem roots (tomato, mum)
  • Petiole (leaf stalk) twisting or epinasty (poinsettia, tomato)
  • Stem thickening (pea, mum, petunia, tomato)
  • Foliage yellowing (mum, impatiens, petunia, lily)
  • Premature fruit ripening (apple, pear, banana, kiwi, cucumber)

Sources and levels required: While illuminating gas is not a common ethylene source today, there are many sources of ethylene including:

  • Exhaust from internal combustion engines (i.e. cars, trucks and non electric powered forklifts)
  • Pollutants released into the atmosphere contaminated with ethylene, including cigarette smoke
  • Emissions from all common floral crops
  • Emissions from fungi such as Botrytis and some bacteria often associated with floral crops
  • Production by plants and flowers that are under physical, water, insect, disease and other types of stresses
  • Banana ripening rooms found in most food distribution warehouses are major sources of ethylene. When the ripening rooms are opened, high amounts of ethylene can be released into the surrounding area, creating problems for nearby flowers and plants.
Temperature: The higher the temperature, the more ethylene produced by plants, and the less it takes to induce plant disorders. Whenever possible, store and display floral crops at the lowest possible temperature without inducing chill or freeze disorders.

Species/cultivar: Grow and handle only species and cultivars that are less sensitive to ethylene. Common plant selection and breeding programs have led to the introduction of many cultivars that are ethylene resistant. In addition, recent advancements in genetic engineering have provided renewed hope for the widespread introduction of ethylene-resistant plants in the near future. Damaged crops (mechanically- and pest-induced): Most damaged flowers and plants-whether hurt mechanically or by insect and disease attack-produce ethylene as a defense. The resultant ethylene can shorten the life of the damaged flowers and plants, but also affect other flowers and plants in the same area, even those not under attack. As the old saying goes, "one bad apple spoils the barrel" - that is, one damaged apple produces ethylene, which in turn damages or spoils otherwise healthy apples nearby. To minimize such damages, handle flowers and plants gently and keep them as free of insects and disease organisms as possible. Potted plant and cut flower sleeves can cause mechanically-induced damages, so remove these sleeves as soon as possible after arrival.

Controlling ethylene action sites: Ethylene will not cause problems unless it attaches to the so-called action sites. Silver from silver thiosulfate (STS) products can prevent or block ethylene from attaching to these action sites, and thus prevent the negative disorders from starting.

Inhibitors of ethylene synthesis: Two anti-ethylene product types (AOA- and AVG-based) can inhibit or reduce the ability of some cut flowers and potted plants to produce ethylene. While these products can be beneficial, inhibitors of ethylene synthesis are generally less effective than STS-based products, since they do not protect against external ethylene. However, some fresh cut flowers do perform well in these solutions, particularly when external ethylene levels are low or when species which have numerous flowers on the same stem at different maturity stages (delphinium, miniature carnation and bouvardia, for instance).

Sanitation: Some fungi and bacteria can produce ethylene. Keep the plants disease free and areas clean where plant materials are grown, stored, shipped or displayed. In addition, discard old or dying plants, flowers and related debris, as these items are potential ethylene sources.

Scrubbers or filters: Mostly potassium permanganate-based, these products have been available for about 20 years. Some plant and flower sleeves also claim to remove ethylene. In addition, some filtering systems use ozone and other chemicals to remove ethylene. These products are only marginally effective. In many cases, exchanging inside storage air with outside fresh air works better and is cheaper.

Air exchange/circulation systems: Most ethylene levels outdoors are too low to cause plant problems. Inside-during periods when workers are not present-simply devise a system to exchange inside with outside air at the rate of one time per hour. During working hours, normal people traffic allows for sufficient air exchange, so your only expense will be energy costs of cooling or heating incoming air.

Positive ethylene effects: Ethylene has a positive side, too. For example, ethylene controls or greatly influences numerous plant growth and developmental processes such as flowering, pigmentation or color development, fruit ripening, leaf abscission or fall, and cell enlargement. While ethylene is needed for plants to properly grow and develop, this gas often becomes a major problem for extending the life of crops after harvest.

Information reprinted from SAF Flower and Plant Care Manual, (Society of American Florists: Alexandria, VA, 1994), pp. 147-150.