Create a Raingarden

For the ultimate in no-maintenance greenery, use native plants to create a water saving garden that captures stormwater from surrounding surfaces

Handyman Magazine, Create a Rain Garden,

Build a raingarden and help save our waterways

The hot new trend in sustainable landscape design, raingardens are taking off all over Australia, particularly in areas of high rainfall.
 
Also called bioretention systems, they comprise beds of free-draining soil with sand underneath, planted with species that thrive even when dry for long periods then saturated during times of heavy rain.
 
A raingarden acts as a living filter for stormwater. The plants draw nutrients from organic matter and fertilisers in the water that would have ended up in rivers and creeks, and the sandy soil collects oil and particulate waste, reducing the sediment and other pollutants in our waterways.
 
In addition to the rain that runs off our roofs, stormwater is washed from driveways, roads, paved areas and other hard surfaces.
 
This runoff can contain pollutants ranging from oil and biological waste like animal droppings and leaf litter to nitrogen, phosphorus and fertilisers.
 
It is directed into the stormwater system and finds its way to rivers and creeks, where it harms aquatic animals and promotes excessive algae growth, reducing oxygen levels in the water.
 
The government is keen to get behind the concept, with Melbourne Water providing a dedicated website on why and how to build a raingarden (raingardens.melbournewater.com.au).
 

The benefits of a raingarden 

Even if you already have a rainwater tank installed, a raised raingarden is great for draining the first-flush diverter, and is invaluable for those times when the rainfall exceeds the capacity of the tank.
 
Runoff from hard surfaces like a driveway, patio or paving that doesn’t make it into the tank can also be used.
 
An inground raingarden can be fed by the drainage channel that collects this runoff and positioned to divert overflow to the stormwater system.
 
It also makes an attractive, functional border for the downhill edge of a patio and is the ideal feature to replace a lawn that gets boggy.
 

Types of rain gardens

There are three main types of domestic raingardens.
 
PLANTER-BOX STYLE are raised, lined garden beds that can be positioned under downpipes, first flush diverters or the overflow pipes of rainwater tanks. They are drained through a slotted pipe in the base.
 
INFILTRATION raingardens allow runoff from paving and downpipes
to filter directly into the soil through layers of sand and scoria, and are planted with deep-rooted species.
 
They reduce the amount of runoff entering the stormwater system and supply clean groundwater.
 
INGROUND LINED designs act as a temporary reservoir for runoff, with a PVC liner preventing direct infiltration into the soil. The water gradually drains through a slotted pipe into the stormwater system.  

Handyman Magazine, Create a Rain Garden, Inground Raingarden

  An inground raingarden is lined with PVC and drains filtered runoff into the stormwater system instead of the soil


Build a rain garden

An inground raingarden is lined with PVC and drains filtered runoff into the stormwater system instead of the soil, so can be sited nearer the house or garage than an infiltration design.
 
TIP Check with council about whether a plumber is needed to modify the stormwater and dial 1100 to locate underground utilities before digging.
 
CHOOSE A SITE close to a water source such as a first flush diverter but at least 500mm from the house to avoid disturbing the foundations.
 
Don’t site it under the canopy of a large tree, as the root system will extend about the same distance.
 
EXCAVATE THE HOLE by pegging out an area large enough to manage the stormwater it will be absorbing, usually about 2% of your roof area.
 
Set stringlines and excavate the bed to a depth of about 1000mm with a gentle slope in the direction
of your existing stormwater system.
 
position the liner along the base and sides of the hole, overlapping the sheets by 200mm and sealing the joints with PVC tape.
 
Add 7mm screening gravel to a depth of 50mm and position 100mm agricultural pipe along the centreline. Use a T joiner to connect one end to the stormwater and cap the other.
 
ADD THE OVERFLOW PIPE by attaching 100mm stormwater pipe to the T joiner, topping it with a grated cap to finish 100mm below ground level.
 
Use lengths of 190 x 45 hardwood to build a border around the hole, securing the PVC liner to the outside of the frame with galvanised staples.
 
FINISH THE GARDEN by backfilling with 7mm gravel to a depth of 200mm. Add a 100mm layer of washed sand then mix four parts sand with one part of topsoil and backfill to 400mm deep.
 
Add suitable plants then mulch with a 50mm layer of pebbles.
 
TIP
Position a layer of geotextile fabric between the gravel, sand and soil mix.

 
 
Handyman Magazine, Create a Rain Garden, Diagram of Inground Rain Garden

Choosing the plants

Raingarden plants have to survive long dry periods then saturation when the water tank overflows. Ask a local nursery about the best plants for your area.

Kangaroo Paw

  • Full sun
  • Up to 900mm high
  • Grows to 1200mm wide
 Handyman Magazine, Create a Rain Garden, Kangaroo Paw

 


Mat Rush

  • Full sun to part shade
  • Up to 1200mm high
  • Grows to 1000mm wide
Handyman Magazine, Create a Rain Garden, Mat Rush plant


Fishbone Water Fern

  • Full sun to part shade
  • Up to 1000mm high
  • Grows to 800mm wide
Handyman Magazine, Create a Rain Garden, Fishbone Water Fern


Yellow Rush

  • Full sun to part shade
  • Up to 1200mm high
  • Grows to 1000mm wide
Handyman Magazine, Create a Rain Garden, Yellow Rush


Matted Pratia

  • Part shade
  • Up to 150mm high
  • Grows to 500mm wide
 Handyman Magazine, Create a Rain Garden, Mattted Pratia

 

Native Iris

  • Sun to part shade
  • Up to 400mm high
  • Grows to 600mm wide
Handyman Magazine, Create a Rain Garden, Native Iris plant
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