• Damaged diseased or dying flowers and foliage including crop debris under benches, in coolrooms and on the inside of dirty buckets.
• Combustion of organic materials such as:
• Car and forklift exhausts.
• Wood coal and kerosine fires.
• Tobacco smoke.
• Ripe fruit.

Exposure of sensitive flowers to concentrations greater than one tenth part per million (0.01 ppm) for short time will cause irreversible damage to these flowers. For every increase in temperature by 10 deg C there is a corresponding doubling of ethylene production by damaged, aging or pollinated plant material. Very little ethylene production takes place unless the material was in poor condition to begin with - a further reason to buy good quality flowers and to store at low temperatures.

Once a flower has started to produce its own ethylene as a result of exposure to ethylene sources, pollination or damage, then it produces ethylene at a rate of 15 time faster than a non-wilted flower. Remove all damaged flowers from bunches as they will affect the others nearby.

Flowers known to be sensitive to ethylene include:

• Agapanthus
• Carnations - causes "sleepiness" ie in-rolling or softness of petals.
• Baby's breath
• Alstroemeria - buds often fail to open
• Freesas - bud often fail to open
• Lilies - especially Asiatic
• Delphinium spp
• Snapdragons - ethylene causes petal and floret "shatter" on many spike-like
• Sweet peas flowers
• Aconitum
• Sweet William Orchids - Cattleya, vanda and Cymbidiums (decreases quality)
• Geraldton Wax
• Tulips - ethylene causes postharvest stem elongation
• Roses - some cultivars fail to open, have abnormal shape, open too fast or drop their Petals and leaves
• Bouvardia
• Veronica

Most of the above flowers have been shown to respond well to treatments that inhibit, or delay, ethylene production by flowers. In recent years silver thiosulphate (S.T.S.) has been shown to be beneficial to many flowers as it inhibits the action of ethylene.

Usually S.T.S. treatment is done by the grower as the immediate postharvest treatment is the most beneficial. However overseas studies have shown that there is some, though decreased, benefit in the wholesaler or florist treating flowers with S.T.S. Some commercial floral preservatives such as Chrysal A.V.B. (r) and Florissant 100 (r) may be convenient for florists to use.

Make sure that you use the correct dose for the time allocated. Longer treatment times especially at higher temperatures may cause burning. For short treatment times use a timer such as a kitchen timer so you can't forget to take the flowers out of S.T.S. solution at the correct time and avoid over treatment. Wear gloves as the concentrate will leave brown stains that take ages to wear off your skin and never washes out of clothing.

Two important additional ways of avoiding ethylene damage are:

1. Store at low temperatures ie close to 1 deg C - except for tropical flowers.
2. Ensure adequate ventilation - a little air movement will dissipate ethylene.

ETHYLENE SCRUBBERS
These will only work if the ethylene comes in contact with the absorber/shrubber. Thus good airflow is most essential.

It is easy to make your own ethylene absorber by making a saturated solution (as much crystals as can be dissolved) of potassium permanganate (Condy's crystals) and pouring this onto florists' foam cut into 12mm thick slices or on to bran. When dry put the foam, or the bran between layers of fly screen wire (or the bran in old stockings) and suspend in front of the fan in the coolroom. Replace when the absorber changes from purple to brown.

DISPOSAL OR ETHYLENE
As silver is a heavy metal there is concern about environmental pollution through disposal of S.T.S. solution. Some commercial preservatives such as Florissant provide chrystals of neutralising chemical to add to the discarded S.T.S. solution.

An alternative method is to place the S.T.S. solution in a tank with a tap at least 10cm from the base. Add sodium sulphide to the S.T.S. solution (I am not sure of the quantity) after this has reacted then pour off the clear 'water' leaving a precipitate of silver salts at the base. This method is not popular with Dutch growers as the silver sulphide smells a lot!