Rain Gardens and Bioswales: Functions, Differences, and Suitable Plants for Australian Landscapes

In contemporary landscape design, especially within urban and suburban environments, rain gardens and bioswales have become reliable tools for managing stormwater while supporting biodiversity and enhancing amenity. Though they serve related functions, these systems differ in form, capacity, and long-term hydrological behaviour.

What is a Rain Garden?

A rain garden is a shallow, vegetated depression designed to capture and absorb runoff from impervious surfaces such as roofs, pavements, roads, or sloping sites. Water collects temporarily within the basin, allowing it to slowly infiltrate the soil, be taken up by plants, or evaporate.

These systems are often integrated into urban streetscapes or residential settings as part of water-sensitive urban design (WSUD).

Characteristics of rain gardens:

• Typically compact and bowl-shaped
• Intermittently wet but designed to dry out between rain events
• Usually underdrained with gravel or sand to promote infiltration
• Require plants that tolerate both short-term inundation and dry spells

What is a Bioswale?

A bioswale, by contrast, is a linear, sloped channel that directs stormwater while filtering out sediment and pollutants. It slows the flow of water, reduces peak runoff volumes, and encourages infiltration where possible.

Bioswales often run parallel to roads, carparks, or boundaries.

Characteristics of bioswales:

• Elongated and gently graded
• Designed for conveyance as well as infiltration
• Sometimes permanently moist, especially at the base of the swale
• May include check dams or gravel trenches to increase retention time

Key Differences and Similarities

Feature	Rain Garden	Bioswale
Shape	Depressed basin	Long, shallow channel
Function	Infiltration and treatment	Conveyance, infiltration, treatment
Water Retention	Temporarily holds water	Primarily slows and channels water
Hydrology	More static, ponding after rainfall	More dynamic, supports flow
Planting Tolerance	Periodic wet/dry cycles	Variable moisture zones across the slope

Despite these differences, both systems require robust plants that can withstand fluctuating moisture conditions, root competition, and nutrient-rich inflows.

Suitable Plants for Australian Conditions

The following native Australian plants are excellent performers in both rain gardens and bioswales:

New Cultivars:

Slim™ Callistemon viminalis ‘CV01’ PBR	Macarthur™ Callistemon viminalis ‘LC01’ PBR
Better John™ Callistemon viminalis ‘LJ1’ PBR	Green John™ Callistemon viminalis ‘LJ23’ PBR
Yalba™ Imperata cylindrica	Isabella® Liriope muscari ‘LIRF’ PBR
Just Right® Liriope muscari ‘LIRJ’ PBR	Amethyst™ Liriope muscari ‘LIRTP’ PBR
Katie Belles™ Lomandra hystrix ‘LHBYF’ PBR	Lucky Stripe™ Lomandra hystrix ‘LMV200’ PBR
Shara™ Lomandra fluviatilis ‘ABU7’ PBR	Evergreen Baby™ Lomandra labill ‘LM600’ PBR
Tropic Cascade™ Lomandra hystrix ‘LHWP’ PBR	Cosmic Pink™ Rhaphiolepis indica ‘RAPH02’ PBR
Cosmic White™ Rhaphiolepis indica ‘RAPH01’ PBR	Grey Box™ Westringia fruticosa ‘WES04’ PBR
Mundi™ Westringia fruticosa ‘WES05’ PBR	Nafray® Pennisetum alopecuroides

Note on Westringia spp.

Westringia species are generally not suited to water-retaining systems due to their intolerance of prolonged wet conditions. However, modern breeding has produced cultivars such as the two cultivars listed above.

It’s important to remember that different varieties belonging to the same species can often behave remarkably differently to each other, and this is the reason plant breeding exists.

Daniel’s Wrap

Both rain gardens and bioswales offer critical contributions to sustainable landscape design—managing stormwater, filtering pollutants, and creating habitat. Selecting the right plants is key to their success.

By utilising native species with proven ecological functions and adaptability, designers can ensure long-term performance and aesthetic value across a range of Australian climates.