Inducing flowering with banana peals

Flowering is a phase which draws rather large amounts of resources from a plant. First of all the parts which make up the flower such as petals, sepals, ovarium and stems aren't built for capturing and storing the sunlight's energy. Depending on the species the flowers often produce nectar, another drain in resources. The growth of pollinea and seeds is a further slice of the energy budget. Annual plants don't have a problem with this: their strategy is to collect as much resources and try to convert as much of it into seeds … within a year. It's not strange that plants have adopted ways of synchronising their flowering: the more plants in cue the more pollination and the better the chance of a return on investment.

Getting everything synchronised is something plants specialise in; they use temperature fluctuations, humidity tresholds, photoperiod and photospectrum to sample the conditions of the habitat. A number of plants have opted to use a cue in the form of a disaster: a fire. A fire in the bush, fynbos or forest has one big advantage: all the plants that compete for the same spot receive a blow. The grasses and other vegetation that can become dense over the years gets thinned out and the remains enrich the organic content of the soil.

A number of orchids have evolved to use these fires to determine the optimum flowering time. This is often accompanied by pollinating insects which emerge or multiply like mad after the same event. The trick is not in surviving a fire (these orchids have underground tubers) but in detecting them. A few orchids found a special way of sensing fires: the underground dormant tuber is sensitive to ethylene gas, a gas which is produced together with propylene in bushfires 1)

We can emulate a fire with smoke-water but this is normally done for getting seeds to germinate, kicking a tuber into flowering-mode is somewhat more difficult: smoke-water treatment means exposing the tuber to high humidity, which can lead to rot. There's however another trick: we expose the tuber to a high dose of ethylene gas. Ripening fruit produces this compound, and the technique is simple: put banana peels in a bag together with the dormant tubers. The content of the bag will saturate in ethylene gas, and this will be picked up by the tuber.

Terrestrial orchids known to respond to banana treatment: 2)

• Pterygodium catholicum (South Africa)
• Leptoceras menziesii (South Australia)
• Thelymitra graminea (SouthWest Australia)

Andrew wrote: Essentially you place the dormant tubers (or even the entire pot) into a plastic bag with a banana peel for 2 weeks. The banana should not touch the tubers as this may encourage fungal problems (putting the tubers in a small tray or a cup inside the bag will do the trick). It's recommended that you replace the banana peel after the first week so that ethylene production is maintained. I replace the skin more often as I find leaving the blackening peel in with the tubers for longer periods can encourage mold. For Leptoceras at least, yearly treatment takes a toll on the vigour of the plant so it's probably best to do it every other year at the most. It doesn't work for all fire stimulated orchids but if you've got a shy flowering orchid that you know is fire dependant it's always worth a try. If bananas aren't available, I suppose any other high ethylene producing fruit can be substituted. Bananas are probably preferred because you don't need to waste the fruit.

The technique is well established among Bromeliad and pineapple growers, the big advantage being that you don't have to make smoke-water.