A STREETSCAPE CHALLENGE

Developed by Starfish Developments, one of South Australia’s most progressive and reliable developers, Hamilton Hill Estate is a new masterplanned community nestled between the urban cityscape and the leafy hills of Adelaide’s prestigious Eastern Suburbs.

Renowned for its high-quality work in Adelaide, Ambience Gardens was engaged to provide the landscaping for the second stage of the development: streetscapes and associated footpaths.

Stage 2 was delivered to great success, with the team at Ambience Gardens encountering and overcoming many challenges it encountered along the way.

One of the primary challenges was the state of the site's soil, which is extremely high in sodium, causing the already heavy clay to compact, leading to waterlogging. The soil is also extremely low in carbon and very alkaline. These attributes occurred as a result of the site being a ‘cut and fill’ site – the site sits on a slope with portions of the ground dug down five or more metres. This profile of the soil is called the ‘accumulation’ zone, which describes an area that accumulates salts and other minerals over hundreds of thousands of years.

Due to these factors, drainage of the site was a key issue. Ambience Gardens came up with a strategy to combat this by installing a perforated agricultural drain pipe along the garden beds and connecting into stormwater pits. A variety of additives, such as gypsum, carbon, compost and sandy soil, were used to ameliorate the soil.

Existing Acer (maple) tree onsite. The Acer genus cannot handle excessive salts and has been damaged from sodium-concentrated soil.

Ambience Gardens developed strategies for the future of the site by selecting appropriate plants and tree species that could cope with the high sodium content, as it will take years many years to flush the salt out of the soil. 

Landscape architects were specified to dig the soil out to 300mm depth and plant the new vegetation. Ambience Gardens designed a soil management plan to ameliorate the soil, with the added benefit of helping the client save money. With this method, Ambience Gardens aims to make topsoil out of the soil that has been buried for thousands of years.

This is continuously being improved and the team is in consultation with soil scientist and advisor Ed Scott from Soil & Land Company Pty Ltd (0403 313 741) to help develop a strategy for improvement.

The importance of drainage, continuous irrigation management to prevent over- or under-watering, and the toxicity of sodium in soil is often overlooked in landscaping. Many landscape architects and contractors will often just dig out 300mm of existing soil and replace with a sandy loam.

The problem the previous contractor of Hamilton Hill Estate had with this was the water sat on top of the compacted existing soil and became anaerobic and, as soon as the trees got the roots into the heavy, salty soil, they slowed growth and experienced problems with excessive sodium. Like us, too much salt for plants is bad for their health. A healthy soil will have around 100 parts per million of sodium and this soil has between 800-1400 parts per million - this is the equivalent of 10 tbsp of salt! 

Ambience Gardens believes the first step to building healthy soil starts with a soil nutrition test and the knowledge to interpret that data. The team recently installed a moisture and salinity probe to measure the soil and salt as it fluctuates, which will further help inform the data as the streetscape continues to grow. 

Let Ambience Gardens help with your next landscaping project. Contact the team via the links below.