Keeping Your Home Safer This Summer

Planning A Fire-Retardant Garden

With bushfires and wildfires becoming more and more explosive and dangerous with each summer, house-holders are increasingly looking to planting fire-retardant or fire-resistant plants. While this is a great idea, it might be timely to reflect on the benefits or otherwise of such plants. (For the purpose of this article, I will use the term 'fire-retardant' to avoid continual use of both terms.)

There has been little research into how effective fire-retardant species really are. If a fire is fierce enough, there is little that will withstand it. However with smaller fires, there is some benefit in having greenery that is slow to catch fire or that burns slowly once it does. Probably the best that can be hoped for is that some species will be less inclined to support fire than others and will burn at a lesser rate. Neither fire-resistant nor fire-retardant means fire-proof.

Fire-retardant plants do not ignite easily from a flame or other source. You should not think you have secured your home against bushfires simply by surrounding it with fire-retardant plants.

Burnt Pine ForestCredit: Wikimedia

In general terms, fire-retardant plants have certain characteristics in common. There will be a high moisture content in the foliage and a low oil content. The volatile oil released by leaves of eucalypts may or may not be hazardous depending on the species and its location. Pines are even more hazardous than eucalypts. The fine leaves of conifers catch fire easily and the resins they contain then burst into fire. Conifers also 'crown' more easily than eucalypts. Crowning is the term used when fire leaps across the tops of the trees.

The leaves of fire-retardant species will be broad. The texture of the bark will be smooth and/or tight. Thick bark will protect dormant buds and sap flow. The amount of dead leaves and twigs held on the plant will be slight. And plants that are high in salt are likely to burn more slowly than others.

By contrast, highly flammable plants contain fine, dry material, have waxy or oily leaves, and are strongly aromatic.

Fire safety procedures which should be carried out in a garden and its surrounds include:

  • Cleaning up and removing garden waste – loose bark and leaf litter is highly flammable. They become tinder-box dry during summer.
  • Pruning and removing dead branches. These, too will be a fire hazard as they dry out. They also trap dry grass and leaves.
  • Cleaning gutters. Embers from bushfires often ignite the leaf mould in gutters so keep your gutters clean.
  • Slashing long grass. Wild oats and dead, dry long grass can fuel a deadly fire. One of the main reasons that fires spread is because there is a continuity of fuel and a large area of long, dry grass provides ongoing fuel.

Another dangerous practice is to plant avenues of trees or shrubs that are in contact with each other. If these are highly flammable species, a fire will be on its way with increasing severity. Aim to create a 20 metre diameter 'circle of safety' around all buildings on the property.

Canberra Bushfires 2003Credit: Wikimedia

A species not endemic to an area will have a different growth pattern and different characteristics when grown outside its local area and a species considered 'fire-retardant' in one area may be much less so in another. Things that affect the development of a species in an area other than its native locale are temperature variations, rainfall, topography and soil structure. Introducing exotic species without due care can result in a plant becoming an introduced weed, with the potential to spread into native bushland, invading and competing with local native plants. An example is the Gosford wattle which is found over quite a large area of New South Wales, Australia. However since being introduced into Victoria it has become a significant environmental weed.

Many of the fire-retardant species are also good at self-regeneration as well as having aesthetic appeal. Some exotic species, while they may be fire retardant, are not so good at regeneration. Those that do recreate themselves can become an environmental pest. An exception to this general rule is the beautiful Magnolia grandiflora or southern Magnolia which comes from south-eastern USA. It is fire retardant, non-invasive and generally very well-behaved.

Some of the plants which may be suitable include plants of the sedum species, vinca species, olive trees and gazania species.

Many of the acacia species have a high water content. Acacia prominens or Gosford wattle is highly ornamental with blue-green foliage and showy lemon-coloured flowers in spring. However, as already stated, it should not be grown outside its native locale.

The Sydney Red Gum (Angophora costata) and other smooth-barked eucalypts may be good choices provided leaf litter is removed. The Sydney Red Gum has great character with its gnarled branches, long drooping leaves and abundant white flower. It is sometimes planted as a spark shield on the fireward side of dwellings. Sparks and embers landing in the canopy do not take hold thus protecting the house from these dangers.

Garden centres should be able to help with suggestions of plants suitable for your particular area. Don't forget – having a gardenful of fire-retardant plants will not automatically protect your home from fire but choosing plants wisely can certainly help make your home less at risk.