Nursery & Garden Industry Victoria | Building Safer Communities

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A carefully designed and well maintained garden is an important addition to every home-owners bushfire plan. It will also provide significant reductions in household energy consumption.

Fire retardant garden design can absorb more of the heat of the approaching bushfire. Fire retardant trees, particularly in windbreaks, can trap embers and sparks and reduce wind speeds near your house, while fire retardant ground covers can be used to slow the travel of fire.

Introduction

The Black Saturday fires of February 7th 2009 provide the catalyst to review current gardening practices with a view to reducing fire risk for homes in regional Victoria.

It is also provides the opportunity for industry and government to incorporate research already completed as a result of other, relatively recent, catastrophic fire events.

Of these the most useful is the material gathered subsequent to the disastrous Ash Wednesday fires. Here we find a great deal of valuable detail regarding the integration of the garden with the twin aims of fire retardation and building preservation.

In particular, research by CSIRO, ACT Government & SA Government, demonstrate that correctly managed vegetation can provide many benefits during a bushfire including:

> reducing fire intensity,

> reducing wind speed,

> deflecting and filtering embers, and

> providing shelter from radiant heat.

It is therefore essential that development on bushfire prone land should require the implementation of a buffer zone between any potential bush fire hazard and buildings, including the family home. This buffer zone is also referred to as an Asset Protection Zone.

It is typically a garden space which is managed progressively to minimize fuel loads and combustibility.

The Asset Protection Zone aims to protect human life, property and highly valued assets.

Some Simple Steps to Protect Building Assets and Human Life

All material immediately adjacent the home and within 1.5m should be non-combustible.

Mulches for example, are very beneficial for plants, however, when organic mulches become dry they become combustible unless they are saturated with water. This should be considered as part of the Asset Protection Plan.

Recommended flame retardant materials include:

> Short green grasses – native or exotic species:

Native and exotic grasses are effective ground covers. They must be trimmed or mown to remove dry material. Whether grown as a lawn or as a ground cover, grass species that retain green foliage over summer are preferable. The home owner must understand that management as well as plant selection and placement are important during the fire season if they are to effectively mitigate fire risk.

With this in mind, and given scarce water resources, grasses which have dried off to brown during summer need to be mown close to the ground. This will effectively reduce fuel loads.

> Ground Covers and Shrubs:

“Interestingly, some of the gardens with Rhododendrons, camellias and azaleas
came out reasonably well and indeed are
credited with saving at least one house
and probably two.”

           Rob Herni - Boolarra Plants
           A wholesale production Nursery
           specialising in growing Native ferns.

Home owners need to avoid plantings that will
grow to be near windows, eaves or doors.

Any plant grown beside or against a wall must be
low to the ground and have limited flammability characteristics.

> Trees

Plant trees at a distance from the house to ensure that limbs and branches do not overhang the roof and gutters do not fill up with debris. The crowns of trees planted at the side of the residence from which the fires can be expected should not touch each other. Select tree species that have low flammability characteristics and have smooth bark. There are many native and exotic species with these characteristics.

there is now a well documented body of evidence which demonstrates the benefits of these plants
in bushfire prone settings.

Home owners need to avoid plantings that produce a ‘fire ladder effect’ where plants provide continuous fuel from lower levels upwards towards the crown of the tree.

Other Factors to Consider

The Black Saturday fires of February 7th 2009 devastated a number of Victorian rural communities and decimated the housing stock in some areas by as much as 70%. The rebuilding process has already begun, under strengthened regulations which should see a much greater degree of fire resistance in new housing stock for these areas.

In Victoria, New building regulations in fire prone areas will result in safer buildings but this needs to be matched with a sensible garden design philosophy that reinforces the survivability of the residence. This can be achieved through careful plant selection, good garden maintenance practices and careful landscape design.

In turn it is important to view these considerations against the three main factors that influence the destructive potential of any bushfire. These are:

> Heat yield

The heat yield of most native vegetation types in Australia is extremely high.

> Rate of spread

This can be influenced by two main conditions – terrain and weather. In turn the nature of the terrain must influence the design of the garden, for example needing to place tall plants at a greater distance from dwellings on the downhill side of any hill.

> Amount and nature of the fuel available

It is absolutely vital that the home owner remove as much potential fuel from around the dwelling as possible. This fuel load will in turn be influenced by the choice of garden plants.

The home owners can reduce many of the significant risk factors associated with bushfires by adopting a strategy based on managing ember attack, lowering fuel loads near the house and using plantings which are slower to catch fire, burn less intensely and burn more slowly.

As well, the following issues should be addressed in any planned garden or any garden renovation in bushfire prone areas.

Windbreaks

A well-designed and maintained windbreak helps protect buildings from bushfires by:

> Reducing wind speed

When fire winds hit a windbreak they are slowed down and forced up and over the trees, creating a protected area on the leeward side.

> Filtering out flying embers

In a bushfire, typically the greatest risk to any residence is embers blown into the house in the strong winds.

Fire resistant trees and shrubs

Trees with leaves containing higher levels of moisture do not normally catch fire from ember attack. They also provide an excellent shield from radiant heat.

Structures and Fences

Structures and fences in the garden will contribute
to the fire risk to the residence.

Structures such as decks, pergolas, and trellis panels should be made from non-combustible materials and ideally not attached to the structure
of the residence.

In the case of fences, consideration may be given to metal fences if sited near the house. Wooden fences should only be built at some distance from the residence.

Amenity and Environmental Benefits

A carefully designed and well maintained garden is an important addition to every home-owners bushfire plan.

The challenge, to achieve a balance between the two competing aims of risk reduction and amenity, can be managed through careful plant selection, siting and upkeep.

A well managed garden will also provide on-going benefits in regard to lowering household energy consumption.

Further Reading

Cooling the Planet, One Backyard at a Time
NGIV – Industry Snapshot, 2008

Landscape and Building Design for Bushfire Areas, Caird Ramsay and Lisle Rudolph,
2003, CSIRO Publishing

Association of Societies for Growing Australian
Plants (ASGAP) Australian Plants for Fire Prone Areas, 1994

Firewise Home Gardens, Information Fact Sheet, ACT Planning and Land Authority

Fire Retardant Garden Plants for the

Urban Fringe and Rural Areas, TAS Rural Fire Service Fact Sheet

Landcsaping For Protection, SA Rural Fire Service, Sep 2000

Fire Retardant Plants, SA Rural Fire Service Fact Sheet Sep 2000