443 Queen Street, a perfect example of sub-tropical landscape design in the Brisbane CBD utilising on slab podium garden beds.
Now you can specify a fully compliant On Slab soil blend in your next project and know it will provide a healthy growing medium for prolonged plant health.
- On Slab soil tested against Specification: E1 & E2 designed by Simon Leake and Elke in Soils for Landscape Development.
- Blends that go far beyond the widely used standards set out in AS 4419:2018
- Blended using AS-4454 compliant compost.
- Free from liquid and industrial waste.
- Incorporating a 16-month slow-release fertiliser, and trace elements to encourage healthy plant growth.
Many landscape industry professionals will be familiar with “Soils for Landscape Development – Selection, Specification and Validation (SLD)” written by Simon Leake and Elke Haege in 2014, highly regarded soil experts. It has become the go-to resource for Landscape Architects, specifiers and contractors around Australia. The manual is a fantastic resource that arms industry professionals with the knowledge needed at the design stage to ensure project gardens meet their full potential.
Quality is King
The team at Centenary Landscaping Supplies have identified a growing demand from both Landscape Architects and landscape contractors alike for soil that is fit for purpose and designed around the detailed specifications laid out in this manual. Contractors are now being held accountable for the soil chosen on projects and are expected to source suitable options based around a rigorous testing regime.
Specifically, our team noted the lack of suitable soils available for On Slab applications which comply with one or a combination of parameters from the Australian Standards 4419:2018 or 3743:2003. Suitable soils for On Slab application is a debated area within the industry, with some professionals calling for a soil based around AS 4419:2018 and some, a soil mix based around the Potting Mix standards AS 3743:2003. These standards have also come under criticism over recent years for lack of detail and set a very low base requirement which arguably does little to support healthy plant growth and development over the life of the garden.
This is where the SLD field manual has become such a valuable resource and built specifications that take into account the requirements within the Australian Standard but are far more encompassing and complete.
We couldn’t find it, so we made it.
In conjunction with the team as SESL (Sydney Environmental Soil Laboratories), we have worked to design and develop soils fit for purpose that meet the rigorous testing parameters laid out by Simon Leake and Elke Haege in SLD, specifically in the area of On Slab application (Specification E1: On slab soil media ‘A’ Horizon & Specification E2: On slab soil media ‘B’ Horizon).
UltraGrow® On Slab A Podium Soil™ and UltraGrow® On Slab B Podium Soil™, have been designed to meet the rigorous testing regime presented in the SLD manual and go far beyond the widely used standards set out in AS 4419:2018. Further, as part of our UltraGrow® Collection, the compost inclusion meets the standards of AS4454:2012 and is achieved completely liquid and industrial waste-free while incorporating a 16-month slow-release fertiliser and trace elements to encourage healthy plant growth.
As noted by the authors of SLD, “…most topsoil supplied by the industry contains excessive organic matter. There is little benefit in having anything more than around 5% by weight (roughly 25% by volume)”. This concept is even more important in podium or slab planting areas where slumpage is a concern, which was have addressed in these new mixes.
Within the industry, there has always been a great temptation to source low cost and ultimately inferior growing media in part due to there often being no requirement for testing and quality assurance checks. It is also currently not the industry norm to source the best quality, most suitable alternative when tendering for projects where cost is a factor.
Even where soils are specified in construction contracts, there has traditionally been a lack of supervision or enforcement. The most common attempt at certification is to ask the soil supplier for an information sheet. These are often non-objective advertising sheets that do not present current or complete test results. The soil specification is often viewed as a cost-saving area, in part due to the soil industry presenting seemingly identical products at a range of price levels and test results that do not truly meet the specification requirements.
With the growing trend for Podium gardens and the Brisbane City Council’s legislated requirement for green spaces and plantings in high rise developments, more and more unfit or poorly designed soil is being installed around South East Queensland. These gardens will likely never achieve full potential in their lifespan which is what drove our desire to create a competitive on slab podium soil blend that is clean, waste-free, encourages growth and meets the spec’s.