Rain is good for a garden until it arrives all at once. Water runs off roofs and paving, pools against walls and washes soil from beds. A well planned garden slows that water down and gives it somewhere useful to go.
This is a design job, not just a plumbing one. Levels, surfaces and plant choices all affect where water travels. The sections below cover the main ideas in plain terms.
Why drainage belongs in the design
Garden styles have changed a great deal, and our look at how landscaping trends have changed over time shows how much fashions move. Water behaviour does not follow fashion. It follows slope, soil and surfaces.
A garden that ignores this can end up with soggy beds, damp walls and muddy paths. Planning for water early costs far less than fixing it after the planting is done. It also gives you more design options, such as a feature bed that doubles as a drainage solution.
Rules and conditions differ between states and councils. The guides quoted below come from Tasmania and South Australia, so treat them as general information. Check local requirements before you build.
Start by sending water away from the house
South Australia’s planning guide for new homes gives a clear starting point. It suggests a paved perimeter about 1m out from the foundation, so runoff drains away from the house and into the garden. It also advises directing runoff away from the dwelling and avoiding waterlogged beds on clay soils.
The same guide says not to direct stormwater at neighbouring footings. It recommends following your engineer’s soil report and site drainage plan. Where needed, sumps or trench grates can collect water at low points.
These steps sound basic, but they set the frame for everything else. Once the water has a safe path, you can start to shape the garden around it. The full list sits in the Adelaide Garden Guide for New Homes.
Use surfaces that let water soak in
Large areas of hard paving shed water quickly. The South Australian guide suggests limiting hard driveway paving to the area vehicles actually need. Elsewhere it suggests gravel, garden beds or other permeable materials.
Paths can be made from steppers, sleepers or pavers with gravel or mulch between them. Entertaining areas can have gaps in the paving, or use gravel or aggregate. Decking over tree root zones lets water soak through to the roots below.
These choices also soften the look of a garden. A path with planting between the stones feels more relaxed than a solid slab. They suit natural planting styles, including the species in our list of native plant options for residential landscaping in Perth.
Build a rain garden where water collects
A rain garden is a garden bed that receives stormwater from a roof, driveway or paved area. Water filters down through the soil. Any excess flows to the stormwater system through underground drainage. The Derwent Estuary Program explains the idea in its guide to rain gardens for the home or business.
The guide suggests placing one at the bottom of a driveway, under a downpipe or beside paved areas. It gives a rule of thumb for size. The bed’s surface area should be at least 3% of the area that drains into it. For example, a 150 square metre roof would need a bed of about 4.5 square metres.
The soil should be a coarse, well draining sandy loam. Under it sits a drainage layer of clean gravel around a perforated pipe. Scour protection is needed where water enters the bed, so the flow does not erode the soil.
The guide advises lining the bed if it is near footings, over a high water table or in salt affected or dispersive soils. It also says a plumbing permit from the local council is required in Tasmania, because the bed connects to the stormwater system. Ask your own council what applies where you live.
Choose plants that cope with wet and dry
Rain garden plants must handle both wetting and drying. The Derwent guide names native dianella, juncus, lomandra and isolepis species as examples. Dense planting keeps the soil active and helps stop the bed clogging.
Plants may need watering while they establish if rain is scarce. If sediment builds up, the guide says to scrape the bed back, till it and replant. That is a light maintenance load for a bed that does a lot of work.
Plant choice matters across the whole garden too. The South Australian guide recommends local native plants because they need less water once established. It also suggests a soil test before design and construction, and amending poor soil with gypsum or organic matter.
Give trees room to drink
Trees need room for their roots. The South Australian guide gives soil areas for planning. It lists 10 square metres of soil for a small tree, 30 for a medium tree and 60 for a large tree.
The guide also warns that some species need clearance from sewer mains. It says root barriers should not be relied on in place of proper footing design. Get advice from a structural engineer or an arborist for trees near buildings.
A well watered, well placed garden also draws wildlife. Birds and frogs like damp, planted corners. Our ideas to welcome wildlife into your yard fit neatly with a rain garden. Once the beds are planted, our tips on how to naturally stop pests can help keep them healthy.
Plan irrigation to work with rainfall
Stormwater design and irrigation are two halves of the same plan. The South Australian guide recommends drip and weeper irrigation, and taps in both front and back gardens. It also suggests automating the system if you are often away.
A rain garden or a well drained bed can cut the amount of extra watering a garden needs. Walk the garden after heavy rain and note where water lingers. Those spots are the best candidates for a rain garden or a permeable path.
Frequently asked questions
How big does a rain garden need to be?
The Derwent Estuary guide gives a rule of thumb of at least 3% of the catchment area. A 150 square metre roof would need about 4.5 square metres of bed. A larger roof or paved area needs a larger bed.
Which plants suit a rain garden?
Choose plants that tolerate both wet and dry spells. The guide names dianella, juncus, lomandra and isolepis as native examples. Plant them densely so they cover the bed.
Do I need a permit for a rain garden?
The Tasmanian guide says a plumbing permit from the local council is required. That is because the garden connects to the stormwater system. Requirements differ by state and council, so ask yours.
How can I stop water reaching my house walls?
The South Australian guide suggests a paved perimeter about 1m out from the foundation. It also advises directing runoff away from the dwelling. Follow your engineer’s site drainage plan.
This article is general information only. Drainage rules and approvals differ by state and council and can change. Speak with your local council or a qualified professional before you build.