This has led to a reduction in biodiversity, as the plants have been absent from home gardens and restoration programs over the past few decades.
Dr Johannes de Lange, a South African botanist with a double PhD, faced a similar dilemma in 1989. He was trying save the Audonia capitalata which was only a few plants around Cape Town. Even after being treated with heat and ash from a fire, the seed he had collected would not germinate. The end was near.
De Langer was engulfed in thick smoke by a sudden wind change during an experimental fire. With watering eyes, he realized that smoke might be the mysterious phoenix factor that would coax the seeds to life. By 1990 he had shown puffing smoke onto soil germinated his rare species in astonishing numbers.
The technique is simple. Create a smouldering fire of dry and green leafy material and pass the smoke into an enclosed area where seed has been sown into seed trays or spread as a thin layer. Leave for one hour and water sparingly for ten days to prevent the smoke from washing out of the seed mix. The rest is up to nature.
Diagram showing the various ways that smoke is applied to seeds. Supplied by Simone Pedrini
Taking smoke germination to the world
Soon after the de Lange discovery, I visited the Kirstenbosch National Botanic Garden in Cape Town. I was shown a few trays of seedlings out the back – some from seeds treated with smoke, some without. The difference was stark. Smoke-treated seeds produced a riot of green, compared to others that resulted in sparse, straggling seedlings.
A tray of seedlings where seed was treated with smoke, left, compared to a non-treated tray. Supplied by author
But was smoke just an isolated African phenomenon, I wondered? Would 150 years of frustrated efforts to germinate some of Australia’s most spectacular and colourful species – from grevillea and fan-flowers to rare native heaths – also be transformed by smoke?
At first, the answer appeared to be no, as every attempt with Australian wildflower seed failed. But after many trials, which I oversaw as Director of Science at the Western Australian Botanic Garden, success came in 1993. Extra time in the smokehouse and a serendipitous failure in the automated watering system resulted in the germination of 25 different species with seedlings. Some were thought to have never been germinated by humans before, such as wild-picked yellow bells (Geleznowia verrucosa) or the giant feather rush (Loxocarya gigas).
Read more: The exquisite blotched butterfly orchid is an airy jewel of the Australian landscape.
This discovery meant for the first time smoke could be used for difficult-to-germinate species for the home gardener and cut flower growers. These days more than 400 species of native seeds , and potentially more than 1,000, respond to smoke treatment. They include kangaroo paw, cotton-tails, spinifex, native bush food tomatoes and fragrant boronias.
Highway plantings, mine site restoration and, importantly, efforts to save threatened plant species now also benefit greatly from the smoke germination technique. For example, smokehouses are now a regular part of many nurseries, which also purchase smoke water to soak seeds for sowing later.
Kangaroo paw seeds respond well to smoke treatment. Supplied by the author
In mine site restoration, direct application of smoke to seeds dramatically improves germination performance. This translates into multimillion-dollar savings in the cost of grain.
Smoke is also a powerful research tool used to audit native soil seed banks, which includes demonstrating the adverse effects of prescribed burning in winter and spring on native species’ survival.
Collaboration with research groups in the US, China, Europe, and South America has expanded the use of smoke to germinate similarly stubborn seeds around the world.