About the book
The Plant Flammability Table
At the heart of ‘Safer Gardens’ is the Plant Flammability Table. This is where you should start if you want to quickly skim the table to find plants which are likely to be safe ones for your garden, or to find information about plants you are already growing. You can then turn to the A-Z section of the book for more detailed information about how those plants fared in flammability tests, as well as other information, such as whether it is considered weedy, toxic, a risk to paving, or if it needs afternoon shade, lots of water, or is eaten by kangaroos. In some cases there will also be information about how that plant performed in bushfires, and how well it recovers post-fire. Keep in mind that all plants burn if the fire is fierce enough.
Below is a sample page from the Plant Flammability Table
Symbols have been used to allow readers to quickly identify things such as flammability level. A dark flame symbol indicates that a researcher considers the plant to be flammable. A clear flame indicates a researcher considers it to have low flammability. Other symbols provide quick references to information such as which State Fire List is used or a plant’s form (S means it is a shrub). To view the key for all of the symbols click here.
You will notice that 4 varieties of rose are featured on this sample page. If you turn to the ‘Low Plants and Climbers’ chapter of the A-Z section of ‘Safer Gardens’, you will find detailed information about those roses. Below are the entries for 2 of them.
Rosa canina - Dog rose
Deciduous climber
Test indicates it has high flammability
Algerian researchers Henaoui et al. (2013) tested plants growing in the mountains. Based on its ignition time in spring they said the green leaf of Rosa canina had high flammability. Moisture content was moderate, length of burning time was high, and flame height was high.
The Country Fire Authority (Victoria) considers all climbers to be extremely flammable.
Weed: Adeclared plant in SA. Naturalised in parts of WA, Tas, NSW, Vic, SA.
Picture by Roberta F courtesy of Wikipedia.
Rosa floribunda - Floribunda rose
Deciduous shrub; may be partly deciduous in warm climates
Test indicates it has low flammability
Sheridan (1996) classed it as fire retardant, based on 12 characteristics, including both the green and dry leaf burning rates. Applying my scale, this indicates it has low flammability. Moisture content was 66.5%. It had the highest mineral ash content (13.7%) and the 5th lowest energy content. She described the foliage as sparsely spaced. It retained a small amount of dry material. She tested exotic and native plants in and around Hobart in summer.
The Tasmania Fire Service said it has moderate flammability. Their rating was for the combined green and dry leaf results, based on Sheridan’s research plus knowledge of its growth habit and characteristics.
Picture by Stan Shebs courtesy of Wikipedia.
Learn more about all the plants in the book
Garden design and plant maintenance
Reducing the risk of fire is not just about the selection of low flammability plants. It is also about garden design and maintenance. For instance poorly placed plants can provide a fuse that leads fire from the garden to the house.
Plants need to be in excellent health to function as an ember screen. If they get readily scorched by the sun or damaged by pests and disease, their flammability will increase.
If possible plants should be regularly watered, according to their individual needs. If you live in an area with really harsh water restrictions it’s best to grow plants that have high drought tolerance.
Choose plants to suit your location. A low flammability plant that comes from a Mediterranean climate will struggle in humid summers. Some plants hate the cold and may be killed by frost.
It’s a really bad idea to use flammable mulch close to a house or shed. Choose hard mulches such as gravel or rocks instead. Don’t grow plants against house walls – if they ignite they greatly increase the risk of windows shattering or embers landing on wooden window frames or other flammable parts of the house.
Hedges can be a fire risk because the act of shearing them and crowding them together creates a lot of dead wood in their interior. Many plants such as wattles, paperbarks and teatrees, tend to develop a lot of dead sections as they age.
Try to get into the habit of regularly inspecting plants. Groundcovers can look lush and healthy but have a thick dead layer beneath the top green layer. It’s very hard to remove this dead material from groundcovers which root as they spread.
Here is a photo revealing some of the dead material beneath the green outer layer of prostrate rosemary.
Here is a photo of the same rosemary groundcover variety (‘Lockwood de Forest’). As you can see it can grow over 3m wide.
Stories from the real world
The book features stories about how plants have fared in bushfires around the world. Although these stories are fascinating and paint a broader picture of how various plants have responded to fire, readers should never rely on them as proof of a plant’s low flammability. By nature this information is subjective and may leave out vital information. Perhaps there was a sudden wind change that saved the plant, or maybe firefighters drenched it with water or it was protected by a stone wall.
The Science
Researchers don’t always reach the same conclusions about a plant’s flammability. One reason for this is that there are no agreed methods for testing plant flammability. Other reasons include plants being tested in different countries or under different conditions. One researcher might test a plant that receives regular irrigation. Another might test plants growing in the wild. One might test a plant in midsummer. Another might test it in midwinter. One might assess a plant based on how long it takes to ignite. Another might combine multiple factors to give it a flammability rating.
Wherever there are conflicting results I lay out the information from the various researchers so that you can make an informed judgement about whether the plant is too risky to grow.
About the author
Lesley Corbett is a writer and a keen gardener who lives in the Perth hills, in the southwest region of Western Australia. Late one night she looked out the window and saw flames in State forest, not far from where she lives. The fire had been deliberately lit. Determined to make her garden more firesafe, she began researching plant flammability. ’Safer Gardens’ is the result of that research. This is citizen science. Lesley does not have a scientific background but became very familiar with the subject in the years she spent researching plant flammability.
Want to know more?
Learn how to structure and maintain your garden so that it has a better chance of surviving a wildfire