As anyone who has sought advice on how to make a garden less combustible will tell you, conflicting advice abounds. The subject of flammability has become a minefield of differing opinions. Winter is a key time for planting trees and shrubs but working out what you are going to plant can be tricky if you want to reduce fire risk.
A new book aims to make the process easier. Safer Gardens: Plant Flammability & Planning for Fire presents some of the most reputable – but often contradictory – information on flammability of particular plants and details how it was determined. The idea is that by giving readers enough of the context, they can draw their own conclusions.
Author Lesley Corbett describes the book as her “citizen science project”. It’s a project that stems from her own close shaves with bushfire, including a particularly fierce blaze that destroyed 57 homes and caused one death not far from her Perth Hills house in 2014.
After that fire, Corbett, who had long considered fire risk in her planting choices, redoubled her efforts to make her garden less flammable. The trouble was, she couldn’t find consistent counsel. Plants deemed to be a low fire risk by some were considered to present a much higher risk by others. She found herself torn about plants to put in and which plants to pull out.
“Take, for instance, the beautiful rainforest tree blueberry ash (Elaeocarpus reticulatus),” she writes. “All the information I came across said it had low flammability, so I planted one at our last house, and when we moved, I planted another one. But then I came across NSW research that found it was the 11th most flammable plant out of the 79 they tested.”
So Corbett bit the bullet, removed her blueberry ash and began delving deeper into the world of plant flammability research. She sifted through scientific research papers and combed through public information put out by fire authorities and others. She didn’t limit herself to Australian work but used overseas information with caution because, as she writes, “flammability is partly determined by local growing conditions”.
She spoke to people around Australia and further afield about their personal observations of how particular plants and landscapes fared in particular fires and she learned about all the different ways in which flammability research has been conducted.
In the absence of established plant-flammability testing guidelines, she says fire experts have used a wide range of techniques to establish ratings. They have conducted tests in different seasons and applied different temperatures. Some researchers tested leaves that were fully green, while others used partially dried ones. Some held leaves in gas flames, some placed them in muffle furnaces, and at least one used an electric radiator.
Nothing was set in stone. When it came to coming up with a flammability rating, some scientists put the emphasis on how long it took a leaf to ignite, while others also considered the height and duration of the leaf’s flame. Some also took into account such characteristics as the thickness of a leaf, bark texture and mineral ash content.