Raingarden DIY: For Homeownners

A raingarden is a great way to help the environment and the health of our local waterways while also creating a self-watering garden in your backyard. Can you create a rain garden yourself? Absolutely! With a little guidance, homeowners can construct a raingarden. But be prepared to sweat!

It doesn't take long to build a raingarden, there is no need for special tools or equipment. All you need is a shovel, a level, and a raingarden soil media.

The soil media is key to the effectiveness of your raingarden. ScapeSpec supplies a premium raingarden mix engineered alongside industry experts to create a superior filtration media that absorbs stormwater runoff from driveways and paved areas during heavy rainfall. It is a specified blend of quality sands, premium topsoil, and rich compost. This blend has been installed extensively on key urban developments, new subdivisions, roads, highways, and carparks (See Projects).

There are two different approaches to creating raingardens:

A.     Backyard Raingardens

To begin building a raingarden in your backyard, the first step is to find or prepare the ideal location. Look around your property to figure out where water runoff goes. The best location for a raingarden is a place that can collect as much impervious(driveway, roof, paths) runoff as possible. A location where water naturally drains, but doesn’t hold water (Figure 1A). Ideally, you want a slight incline rather than a steep slope.

Be aware of any underground services in your backyard. If you are not sure about it, you can always contact your local councils and ask for advice.

Placing your raingarden near runoff sources, like driveways or sump pumps, will act to disperse water runoff and stop it from reaching your home's foundation. Build your raingarden at least 3 metres away from your house to prevent damage to the foundation.

Most backyard raingardens are 10 to 30square meters in size. However, they can be sized according to the space you have or the amount of runoff you are looking to retain. Some homes may have multiple problem spots and benefit from more than one raingarden.  

Once you've determined the size, depth, and shape, you can map it out on the ground using marking paint before you excavate. Dig the area to your desired depth, dependent on the permeability of the soil bed and quantity of runoff (Figure 1B). Slope the soil downward from the outside to the centre, where it should be the deepest.

Move the earth you have excavated to the lowest side of the raingarden, on the downhill, to form an edge or low bank to help contain the soil and water (Figure 1C). This berm must be quite solid to prevent washout.

When you have finished digging, place the raingarden soil blend into your pit and level it out (Figure 1D). Place some splash rocks in the inlet to control erosion and add visual interest.

Once you have built the foundation of your raingarden it is on to the planting – the creative part. The beauty of a raingarden is it can provide you with a great garden aesthetic while also saving our waterways and your property (Figure 1E).  

Once you've completed your planting, cover your garden with a woodchip or shredded mulch 5-7 centimetres thick. Avoid using lighter mulches as they will float in water and maybe be washed away to the edges of the raingarden.  As well as hindering weed growth, this will aid in maintaining adequate moisture for optimal plant growth.

Figure 1. Creating a raingarden. A: Find the ideal location, B: Dig to your desired depth, C: Use the excess soil to form an edge, D: Fill with raingarden blend and place splash rocks, E: Plant shrubs and apply mulches

B.     Driveway-adjacent Raingardens

To build a driveway-adjacent raingarden in your backyard, the first step is to find or prepare the ideal location. Look around your driveway to figure out where water runoff goes. The best location for a raingarden is a place that can collect as much runoff a (Figure 2A). Most driveways have a slight incline that redirects water.

Be aware of any underground services in your backyard. If you are not sure about it, you can always contact your local councils and ask for advice. Build your raingarden at least 3 metres away from your house to prevent damage to the foundation.

Normally, driveway-adjacent raingardens are tenth of the driveways area. However, they can be sized according to the space you have or the amount of runoff you are looking to retain. We highly recommend having a look at your local council guidelines to know more about rain gardens and regulations (for reference Auckland, Waikato, Canterbury).

Once you've determined the size, depth, and shape, you can map it out on the ground using marking paint before you excavate. Dig the area to your desired depth, dependent on the permeability of the soil bed and quantity of runoff (Figure 2B). Slope the edges downward from the outside to the centre, where it should be the deepest.

When you have finished digging, place the drainage material into your pit and level it out (Figure 1C). Check this link to find out more about different types of drainage layers available in the market (See link)

Then, place the raingarden soil blend into your pit and level it out (Figure 1D). Place some splash rocks in the inlet to control erosion and add visual interest.

Once you have built the foundation of your raingarden it is on to the planting – the creative part. The beauty of a raingarden is it can provide you with a great garden aesthetic while also saving our waterways and your property (Figure 2E).  

Figure 2. Creating a raingarden. A: Find the ideal location, B: Dig to your desired depth, C: Place the drainage layer, D: Fill with raingarden blend and place splash rocks, E: Plant shrubs and apply mulches

Once you've completed your planting, cover your garden with a woodchip or shredded mulch 5-7 centimetres thick. Avoid using lighter mulches as they will float in water and maybe be washed away to the edges of the raingarden.  As well as hindering weed growth, this will aid in maintaining adequate moisture for optimal plant growth.

Different species are likely to thrive in different areas of the garden. When selecting your plant palette always promote natives as they are hardened to our local conditions and support our ecosystems. In general, select native species that withstand prolonged periods of ponding and drought. Toward the edge of the bed, place plants that are more drought-resistant and in the centre or deepest part of your garden, plant species that can handle ‘wet feet’ for short periods (Figure 3). Moisture-loving species may not thrive in your raingarden.

For a non-fail high-performing raingarden, you could select hardy native rushes such as Apodasmia similis (Oioi; jointed rush) and Ficinia nodosa (Knobby club rush; Wiwi).

If you are after a softer, more diverse native plant palette, select grasses such as Phormium’s(Wharariki) Cookianum or Green Dwarf, Astelia grandis (Swamp astelia), and members of the Carex family (Carex virgata or Carex secta). Other plants that work well in free draining areas of raingardens are Coprosma ‘poor knights’, Mulehnbeckia complexia, and Arthropodium cirratum.

Figure 3. Raingarden's construction and planting plan

The RG240 raingarden media blend will provide your plants with a good foundation. It is best not to use fertilizers, herbicides, or pesticides, as they may impact or pollute water quality. However, occasional watering of the plants may be necessary during dry seasons. Past the first year, maintenance is usually minimal.

Now you can sit back and enjoy a thriving garden, with the knowledge of the environmental benefits happening under the surface. Raingardens play a vital role in water management to keep our beaches pristine for generations to come.

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