Rain garden

It’s raining – proper rain that is soaking the ground and has been falling on an off through the night and this morning. So I thought I would revive the following piece, written in 2009.

The Western Bay of Plenty is renowned for its plenty, including plenty of rain. But how many home gardeners are aware they can help slow and treat the run-off from their property by creating a rain garden?

Tauranga City Council has developed a rain garden at a reserve in Pillan’s Point, although engineering technologist Celia Bowles said it was still at an experimental stage.

“We’re building up our expertise on the design, maintenance and operation of a rain garden,” she said, “but there aren’t any plans yet to put more in.”

Kip Cooper, a civil engineer with Beca, said rain gardens can be useful in private or commercial situations – as well as controlling the volume of water flowing from a property, they can also help control the quality of the water running into Tauranga Harbour by removing contaminants such as zinc (from roofs), copper (from, say, spouting) and sediment.


A green roof and rain garden at Auckland Regional Botanic Gardens. Photo: Sandra Simpson

“If you have a place where you always wash your car, you could allow the run-off to wash through a rain garden before it enters the stormwater system to help remove contaminants,” Kip suggested.

The commercial application of rain gardens sees them positioned beside busy roads and in carparks to filter road and vehicle contaminants from rain water.

“In that situation, you have to choose plants that can cope with heavy metals,” he said, “and reeds are pretty good at that. There are plants that can store the contaminants or break them down.”


The 2008 rain garden by Auckland designer Kirsten Sachs. Photo: Sandra Simpson

Rain gardens can be as elaborate as the one designed by Auckland landscaper Kirsten Sach for the 2007 Ellerslie Flower Show that featured slim-line water tanks hidden in plaster walls, or as simple as the one she designed a year later for the Auckland Flower Show that comprised a downpipe running into a stepped system.

On top was a pond (complete with goldfish and aquatic plants), that overflowed into a box planted with wet and dry-tolerant plants that, when  conditions are right, overflows to a stony bed garden.

The garden won gold  and was created for $6000, including the shed the water ran off.

Kip described a rain garden as a “tier system” in that the water gradually moves through the planting and soil and gravel and is filtered along the way.

“They are great things,” he said, “because one day they’re flooded and the next day they’re dry. You need flora that can cope with that, but it’s an ideal opportunity to vary what you have in your back garden.”


Rain collection by Carl Pickens at the 2009 Ellerslie show. Photo: Sandra Simpson

Landscape designer Carl Pickens showed decorative rain collection in his award-winning 2009 Ellerslie International Flower Show garden. The small bowls acted like a chain in that water ran down the links and finally into the large bowl which then overflowed into the adjacent reed bed.

Further reading:

This article was originally published in the Bay of Plenty Times and appears here with permission. It has been updated slightly.