Fire-Retardant Plant Cultivars for Brisbane’s Climate: A Guide for Landscape Architects

For landscape architects, an understanding of the local climate and the types of plants that thrive in it is essential. This knowledge becomes even more critical in bushfire-prone areas like most cities in Australia including Brisbane, where the choice of plants can have a significant impact on fire safety.

This article aims to guide landscape architects in selecting suitable fire-retardant plants that not only thrive in Brisbane’s climate but also contribute to the overall aesthetic and functional value of the landscape.

Why Should We Care about Fire Safety, Anyway?

We don’t need a reminder of the devastation bushfires can cause in Australia.

Just four years ago, we experienced widespread bushfires around the country – it was so bad that the season was dubbed the “Black Summer.” We were lucky to escape relatively unscathed in Brisbane, however on October 8, a severe and fast-moving fire destroyed a house at Thornton and threatened the nearby township of Laidley, just west of Brisbane.

The rest of Brisbane is just about due for a wake-up call – I don’t know if you like to go on bush walks like I do, but there’s a lot of leaf litter and organic debris around the place that’s just begging to go up in flames.

Understanding Fire-Retardant Plants

Fire-retardant plants are those that, due to their specific characteristics, are less likely to ignite during a bushfire while dampening a fire’s effects. These traits may include a high moisture content, low oil or resin content, and an overall ability to resist ignition.

However, it’s important to note that while these plants are less likely to ignite, they cannot entirely prevent a bushfire. They can, however, slow down the spread of fire, providing crucial time for emergency services to respond. They can also help create defensible spaces and evacuation routes.

The term “fire retardant” signifies that these plants not only resist fire, but actively subdue it, while the term “fire resistant” signifies that something is able to withstand fire, such as a metal pole or a rock. There’s a subtle but meaningful distinction between these two terms.

The Role of Fire-Retardant Plants in Landscape Architecture

Landscape architects can strategically incorporate fire-retardant plants into their designs, creating defensible spaces and firebreaks that help protect structures and allow for safer evacuation routes. These plants can be used in conjunction with other fire-resistant design elements such as hardscaping and strategic spacing between plantings to create a comprehensive fire-safe landscape plan.

But plants rarely ever serve a singular purpose. The fire-retardant plants we’ll be talking about here contribute significantly to a landscape’s aesthetic and functional value. With their unique textures, forms, and colours, they can enhance visual interest and diversity within the landscape, while also being touch enough to withstand drought and/or wet feet.

Top Fire-retardant Plants for Brisbane’s Climate

Here are some of the best fire-retardant plants that will thrive in the Brisbane climate:

Queen Mum™ Agapanthus orientalis ‘PMN06’ PBR

Queen Mum™ Agapanthus orientalis ‘PMN06’ PBR is a striking plant with glossy green strap-like foliage. It exhibits excellent disease tolerance and can withstand frost, drought, and humidity, making it a resilient choice for Brisbane landscapes. Its fire-retardant properties stem from its high moisture content and low oil content. Regular watering and full sun to partial shade will keep this plant thriving.

Just Right® Liriope muscari ‘LIRJ’ PBR

Just Right® Liriope muscari ‘LIRJ’ PBR is a more evergreen alternative to the Evergreen Giant. Over the past 8 years, it has rarely, if ever, produced viable seed, making it a safer choice for areas close to bushland. This plant requires minimal maintenance and thrives in full sun or partial shade, making it an excellent choice for Brisbane landscapes with variable sunlight.

Aloes

In general, succulent plants like pig face and aloes are fire-retardant, due to the high moisture content in their leaves. Here are a few of the best aloes that will survive in Brisbane:

• Sea Urchin™ Aloe hybrid ‘ANDsea’ PBR,
• Mighty Coral™ Aloe hybrid ‘AL04’ PBR,
• Mighty Gold™ Aloe hybrid ‘AL02’ PBR

Aussie Rambler™ Carpobrotus glaucescens ‘CAR10’ PBR

The Aussie Rambler™ Carpobrotus glaucescens ‘CAR10’ PBR is a prostrate creeping succulent characterised by long trailing stems up to 2m. It produces extra-large deep pink flowers in spring and autumn, adding a vibrant touch to any landscape. As a succulent, it retains a lot of water, reducing its likelihood of ignition during bushfires. This plant thrives in well-drained soil and full sun.

Lomandra

CSIRO did a test study in 1999 in conjunction with the Victorian Department then known as the Department of Sustainability and Environment, where they found that lomandras were much slower to ignite than other plants.

Here are some of the best lomandras for Brisbane:

• Shara™ Lomandra fluviatilis fluviatilis ‘ABU7’ PBR,
• Tropic Cascade™ Lomandra hystrix ‘LHWP’ PBR
• Katie Belles™ Lomandra hystrix ‘LHBYF’ PBR

Kangaroo Paws

Just like lomandras, kangaroo paws are strappy leafed bush plants that you might assume are fire-prone, but are actually good fire-retardant options. Here are two of the best options for Brisbane:

• Anigozanthos hybrid ‘Amber Velvet‘ PBR
• Everlasting Mega Gold™Anigozanthos hybrid ‘KP03’

Turf Grasses

As long as turf grasses don’t get too dry or long, they often have excellent fire-retardation properties. Zen Grass Zoysia, being a low mow lawn only requiring a yearly cut in Brisbane, is an excellent choice.

• Zen Grass Zoysia spp. ‘ZOY01’ PBR Intended

Trees

In general, evergreen rainforest plants (lilly pillies, tristaniopsis, ficus, etc) are more fire retardant than scrub-dwelling plants like many species of eucalypts.

Even though some of these plants do have oil content, for example in lilly pillies which have their signature oily scents, their high moisture content can prevent them for catching fire.

Here are a couple of great options that will thrive in Brisbane:

• Luscious® Tristaniopsis laurina ‘DOW10’ PBR
• Sweeper® Waterhousea floribunda ‘DOW20’ PBR

Hedges

Lush hedging makes plants less likely to burn than dry material, particularly when the shrubs have high moisture and low oil content to begin with. Here are two quick-growing hedge plants that thrive in Brisbane:

• Dense Fence™ Viburnum odoratissimum ‘VOC1’ PBR
• Quick Fence™ Viburnum odoratissimum ‘VOQ1’ PBR Intended

Maintaining Fire-Safe Landscapes

Proper maintenance plays a crucial role in creating fire-safe landscapes. The first step is to ensure that you regularly remove dead vegetation and fallen leaves from your garden, as these can serve as fuel for potential fires. Pruning your plants, especially the lower branches of trees, can help to prevent a ground fire from climbing up into the canopy.

However, it’s essential to be mindful of the timing and extent of your pruning activities. Over-pruning can lead to the growth of dense, flammable vegetation. Watering your garden adequately is another key aspect of maintaining a fire-safe landscape. Plants that are well-watered are less likely to catch fire compared to those that are dry and parched.

It’s also advisable to use a soaker hose or drip irrigation system, as these methods deliver water directly to the plant roots and minimise evaporation. Additionally, consider using non-flammable mulches such as gravel or decomposed granite (although there’s a trade-off here regarding the fact that they can become quite hot and “cook” the soil).

While organic mulches like straw or wood chips can help retain soil moisture, they can also be highly flammable.

Incorporating Fire-retardant Plants into Your Landscape Designs

Strategically integrating fire-retardant plants into landscape designs is a crucial aspect of creating resilient spaces in bushfire-prone areas. Here are some practical tips for doing so:

1. Consider Growth Habits: Take into account the growth habits of the plant, such as its mature size and form. This will help determine the most appropriate location in your design, ensuring that the plant can grow to its full potential without causing obstruction or overcrowding.
2. Maintenance Requirements: Understand the maintenance needs of each plant. Some may require regular pruning to maintain their fire-retardant properties, while others may need specific soil conditions to thrive. Healthy plants with moist leaves tend to be more fire retardant than struggling or dead plants.
3. Aesthetic Appeal: While the functional role of these plants is paramount, their aesthetic contribution to the landscape should not be overlooked. Consider the plant’s texture, colour, and seasonal changes when planning your design.

While fire-retardant plants play a critical role in bushfire-prone areas, incorporating a variety of plant types can enhance biodiversity and create more visually interesting landscapes. Consider complementing fire-retardant species with other native plants, trees, and shrubs that are well-adapted to Brisbane’s climate, without planting fire-prone plants close to one another.

Daniel’s Wrap

Fire-retardant plants are a vital component of landscape design in bushfire-prone areas like Brisbane. They not only contribute to the safety and resilience of outdoor spaces but also add to the overall aesthetic and functionality of the landscape. As a landscape architect, consider these plants in your future projects. However, it’s important to remember that while these plants can reduce the risk of fire spread, they are not a silver bullet solution.

Relying solely on plant selection is not enough to stop a bushfire. Other preventive measures, such as maintaining an appropriate distance between plants, regular pruning, and removing dead vegetation, should also be taken. By combining thoughtful plant selection with comprehensive fire-safe landscape practices, we can create beautiful, functional, and resilient landscapes that stand the test of time.