The Invisible Crop Destroyer: Ethylene is an odorless, colourless plant hormone gas that accelerates senescence (aging). In concentrations as low as 0.01 parts per million (ppm), it causes irreversible petal wilting, bud abortion, and floret shatter.
1. Major Sources of Ethylene
Ethylene is produced naturally by plants and generated through the combustion of organic fuels:
- Decaying or Diseased Material: Damaged, dying, or decaying flowers and foliage under packing shed benches, inside dirty coolrooms, or lingering in unwashed buckets.
- Exhaust Fumes: Internal combustion engines from delivery trucks, vans, and petrol or diesel forklifts.
- Combustion Heaters: Kerosene, gas, wood, or coal space heaters.
- Tobacco Smoke: Cigarette smoke contains significant ethylene concentrations.
- Ripening Fruit & Vegetables: Bananas, apples, tomatoes, melons, and avocados produce intense ethylene plumes.
Self-Accelerating Cascade: Once a flower is exposed to ethylene, pollinated, or damaged, it begins producing its own ethylene at a rate up to 15 times faster than fresh blooms. Furthermore, for every 10°C increase in temperature, ethylene production doubles!
2. Ethylene-Sensitive Commercial Crops
Carnations
Causes “sleepiness” — petal in-rolling, softening, and premature closure of open flowers.
Snapdragons & Delphinium
Triggers severe petal and floret “shatter” — individual florets fall rapidly off the flower spike.
Lilies (Asiatic & Oriental)
Causes bud yellowing, failure of unopened buds to mature, and premature flower drop.
Alstroemeria & Freesias
Flower buds fail to open; foliage yellows prematurely.
Roses
Cultivars fail to open, develop distorted shapes, open excessively fast, or shed petals and leaves.
Orchids (Cymbidium, Vanda, Cattleya)
Lip discoloration, petal fading, and severe reduction in vase display longevity.
Baby’s Breath (Gypsophila)
Rapid dehydration, florets fail to open, and brown discoloration.
Geraldton Wax & Bouvardia
Extensive petal and leaf drop within 24 hours of trace exposure.
3. Prevention & Cold Storage Control
Two essential post-harvest practices significantly reduce ethylene risk across all handling facilities:
- Low-Temperature Storage: Store blooms as close as possible to 1°C (except tropical varieties). Cold temperatures suppress both ethylene synthesis and plant tissue sensitivity.
- Adequate Ventilation: Continuous gentle air circulation dilutes and dissipates localized ethylene buildup.
- Post-Harvest STS Loading: Silver Thiosulphate (S.T.S.) treatment blocks the plant’s ethylene receptors. (See our dedicated S.T.S. Guide).
4. Coolroom Ethylene Scrubbers
Commercial ethylene scrubbers or DIY potassium permanganate absorbers remove airborne ethylene through oxidation. Good coolroom airflow is essential so that air actively circulates through the filter medium.
How to Build a Saturated Potassium Permanganate Scrubber:
- Dissolve potassium permanganate (Condy’s crystals) in water until no more crystals dissolve (saturated solution).
- Pour the deep purple solution onto 12 mm thick slices of floral foam or raw bran.
- Allow to dry completely.
- Enclose the dry foam or bran between layers of flyscreen wire mesh (or fill nylon stockings with the bran).
- Suspend the scrubber directly in front of the coolroom fan intake so all circulating air passes through it.
- Replacement Indicator: Replace immediately when the chemical changes color from purple to brown (indicating exhaustion).
5. Safe Chemical Handling & STS Disposal
Silver is a heavy metal and must not be poured directly down municipal storm drains or onto farm soils. Commercial preservatives like Florissant supply neutralizing crystals for spent solutions.
Alternatively, growers precipitate silver from solution in a dedicated tank by reacting with sodium sulphide, settling insoluble silver sulphide salts at the bottom before drawing off clear neutralized liquid.
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