House has inadequate drainage?

 In Building


Inadequate drainage in part of the garden is a problem that affects many gardeners. The problem can be a constant one where it occurs all year round or it may be seasonal. It might be that the stormwater drains into one corner of the yard resulting in at best moist soil and at worst a complete bog. It may be just a low spot that collects all the water from the surrounding area. Whatever the reason, there are ways of turning a boggy or wet area to your advantage. Some plants thrive in wet areas, and with the right plants, you can still achieve an interesting and attractive garden in a wet area.

What can cause wet areas in your garden?

  • Leaking pipes.
  • Wastewater from your house that is drained into your garden.
  • Rising water table (e.g. particularly from over-irrigation in rural areas) or naturally occurring springs
  • Water from surrounding properties may drain into your garden. This could be naturally occurring or may result from your neighbours diverting water, either intentionally or unintentionally, from their property into yours.
  • Low areas or depressions provide a site for water to collect. The water could be from rainwater, garden irrigation, etc.

Problems with wet areas or inadequate drainage

  • High levels of moisture around the house increase the possibility of structural movement and or subsidence in the footings. Adelaide has very reactive clay soils, which expand during the wet seasons and contract during the dry. It is important to try and stabilise this ground moisture content.
  • High moisture also increases the risk of a possible termite infestation.
  • The presence of stagnant water can be a health hazard. It can also be very smelly.
  • Access is restricted (e.g. you can sink into muddy areas)
  • Visually the area may look quite ugly. It may also be quite messy for kids and animals (fence off or plant so densely that access is restricted).

inadequate drainage


Wet areas can be overcome in the following ways:

  • Prevent or reduce the amount of water reaching the garden. For example, blocked drains can be repaired, leaking pipes can be fixed, stormwater diverted elsewhere, etc.
  • Fence off, or plant trees and shrubs to screen the area off. This can prevent access to the wet area as well as blocking it off visually. It doesn’t however, fix the problem.
  • Improving drainage

For heavy clay soils:

  • Dig in lots of organic material (e.g. mulch or wood shavings). As this decomposes it improves soil structure and nutrition, helping drainage as well as increasing the soil’s capacity to absorb water.
  • Add gypsum or Multicrop’s clay breaker. These products open up hard soils allowing better drainage.
  • Install drainage pipes to take the water away.

For low spots:

  • Dig organic matter into the soil to help absorb excess water and improve soil structure.
  • Create a sump pit at the lowest point (see the section on creating a sump)

Raise Levels or Fill Depressions

Get an earthmoving machine in (or do it by hand if it’s not a big job) and change the levels of your property so water drains away instead of collecting in any one part. Build a raised garden bed on the surface of the ground.

  • Plant with water-loving plants, 
    • If the area is always wet
      • Use plants that like continuously wet soil, and do not mind being waterlogged at times (e.g. Iris, Papyrus etc.). Spread a 4 – 5 cm layer of coarse sand or pebbles over the surface to restrict the growth of algae or any other putrid smells
    • If the area sometimes dries out:
      • Create a bog garden by digging out the area, lay a double thickness of black plastic, fill with a good quality, highly organic compost then plant with bog plants.
      • Use plants that tolerate or even like being waterlogged but will tolerate some drier periods.
  • Build a pond and drain surface water into the pond.


Often the home gardener will find that they have nowhere to drain excess water to. One way of inadequate drainage is to dig a sump. Try to avoid placing it near other pipes, drains, etc. The technique for creating a sump is as follows:

  1. Excavate a hole approximately 1 m wide x 1.5 m deep. The soil removed can be used elsewhere or discarded.
  2. Fill the hole to within 300 mm of the surface with coarse material such as rubble, rocks, etc.
  3. Lay your drains so that they terminate (discharge) level with the top edge of the rocks.
  4. Add a layer of 150 mm of sand, then fill the remaining part of the hole up to ground level with a good quality sandy loam or loam soil.
  5. Plant lawn or other plants over the excavated area.

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