Artificial Grass in Hornsby

Five soil landscapes, one suburb

The percentages below come from geometric intersection of NSW Government soil landscape polygons with the Hornsby suburb boundary, and the descriptions are quoted from the official per-unit reports.

• Hawkesbury, 36.7%. Hawkesbury Sandstone with rock outcrop over half the surface, described as a "shallow, stony, highly permeable soil".
• Glenorie, 23.9%. Wianamatta shale, "moderately reactive", with "Low permeability" and localised seasonal waterlogging.
• Lucas Heights, 20.9%. Mittagong Formation, permeable topsoil over a subsoil the report calls "occasionally sodic and impermeable".
• Gymea, 7.3%. Sandstone again, "shallow highly permeable soil", "freely drained", "stable to slightly reactive".
• Hornsby, 5.3%. "Deeply weathered basaltic breccia", with a "highly plastic, low wet-strength, highly reactive subsoil".

Add the two sandstone units together and about 44% of the suburb is free-draining rock country. Add Glenorie to the reactive end and roughly a quarter is shale clay that behaves in the opposite way. Those are the whole-of-suburb figures for the mapped polygon, including bushland, roads and reserves, and the mapping is at 1:100,000 scale. The reports describe themselves as an inventory of soil and landscape properties rather than a substitute for site investigation, so none of this tells you what is under your back lawn. What it does tell you is that in Hornsby the odds of guessing wrong are unusually high.

What shallow rock does to an excavation

A typical residential turf base starts with excavating around 75mm of existing soil, deeper where vehicles will drive on it, before any membrane, road base or sand goes in. On the sandstone side of Hornsby that excavation can meet rock before it reaches depth, because the Hawkesbury unit is mapped with outcrop across more than half its surface and the soil above it is shallow by definition.

That is not a reason to abandon the job. It does mean the installer has to choose between building the level up rather than cutting down, reworking falls across the yard so the finished surface still sheds water, or bringing in gear to break rock. Those options carry very different costs and very different amounts of noise and mess, and they are decisions best made standing in the yard. The upside of sandstone country is real too: freely drained ground under a permeable base is a much easier drainage problem than heavy clay. Our walkthrough of turf installation on a Hornsby block covers the layers involved and where the choices sit.

What reactive clay does over a season

The other half of the Hornsby story behaves nothing like the first. Reactive soils swell as they take up moisture and shrink back as they dry, so the ground itself moves through a wet winter and a dry summer. The Glenorie unit that covers about a quarter of the suburb is described as moderately reactive with low permeability and localised seasonal waterlogging, meaning water sits rather than soaks. The Hornsby diatreme unit goes further again: a highly plastic, low wet-strength, highly reactive subsoil, the most reactive description in the whole dataset.

For a lawn, low permeability is the practical issue more often than reactivity is. Water that cannot drain through the soil below has to be taken somewhere by the base, which is why a compacted, properly graded sub-base and a real drainage plan matter more on the shale side of Hornsby than on the sandstone side, where the ground does much of that work for free. To be clear about what we are not saying: there is no Australian Standard that specifies excavation depth or base build for artificial turf as a function of soil reactivity, and nobody can classify your site from a map. Soil reactivity is a building standards concept for footings and slabs, not a landscaping rule. It is simply a good description of how your ground handles water.

Why the site visit earns its keep here

In a suburb built on one soil type, a phone estimate per square metre is a reasonable approximation. In Hornsby it is closer to a coin toss, because the two most common grounds pull the preparation in opposite directions and there is a small chance of the most reactive material in Sydney under the lawn.

Questions worth asking whoever quotes you: what depth are you excavating and what happens if you strike rock; is rock breaking inside the quote or a variation; where is water going once the base is in and the surface no longer soaks in place; and is drainage work itemised separately from the turf rate. An installer who has walked the block can answer all four. One who has not will usually answer with an average. That is also why the ground conditions, not the turf itself, are the line item most likely to move a Hornsby quote away from the Sydney middle of roughly $90 to $140 per square metre installed.

Trees, shade and what falls off them

Hornsby is leafy in a way that is not decorative. Large parts of the suburb sit at the bushland interface with mature eucalypts on or beside the block, and the shade those trees throw is the reason a lot of Hornsby lawns fail in the first place. Synthetic turf has a structural advantage here: it does not need sunlight, so the worn strip under a canopy where grass has given up can hold an even surface year round.

The trade-off is what comes down off the trees. Leaf drop, bark and gumnuts on a treed block are constant rather than seasonal, and left in place they break down into a fine organic layer that blocks the drainage perforations in the turf backing. A shaded yard also dries slowly, so blocked drainage and trapped moisture together are how mould and weed seed get started. The debris matters for drainage, not just for looks, which is a different argument than most maintenance advice makes. For the actual routine, brushing, rinsing and how often, see our guide to cleaning and maintaining artificial grass in Sydney. Root systems are the other planning item: an established tree's roots run wider than its canopy, and a base is normally worked around them rather than through them, which is one more thing that has to be seen to be planned.

Hornsby nature strips: what Council actually publishes

Honest answer: Hornsby Shire Council does not publish a specific position on synthetic turf on the nature strip. We looked, and we are not going to invent a rule to fill the gap. What is certain is the general position: works on the verge require council approval under the Roads Act 1993 and the Local Government Act 1993, so a conversation with Hornsby Shire comes before anything gets laid out the front.

It matters because Sydney councils are genuinely not consistent on this, and neighbouring is no guide at all. The Hills Shire, immediately to the west, publishes one of the most detailed positions in the state: "The use of synthetic turf on the council nature strip is not accepted in the Hills Shire except where poor growing conditions such as total shade is present." Strathfield's adopted policy is blunter again: "Property owners are not permitted to replace natural turf on nature strips with synthetic turf." Two councils, two different rules, and Hornsby publishes neither. Assume nothing and ask.

The distinction almost nobody spells out is the useful one: all of this is about the nature strip, which is council land between your fence and the kerb. None of it applies to your own front or back yard. If you are weighing up the front yard as well, our overview of synthetic grass for Hornsby homes covers product tiers, what drives a price and the questions worth asking before booking anyone.

Dogs, kids and bushland blocks

The larger, treed blocks common through Hornsby suit dogs, and a dog changes the specification rather than the concept. Drainage capacity, backing perforation and infill choice all shift for a pet household, and on a shaded block that drains slowly the drainage side of that matters more than it would on an open sunny yard further west. Where a dog patrols a fence line or cuts the same diagonal across the yard, extra compaction along those lines is cheap at the start and disruptive to add later. The specifics are on our page about turf for dogs.

One thing to set expectations on: there is no turf rebate anywhere in Australia, from any council or water utility. Sydney Water's water wise guidelines do restrict watering with drinking water to before 10am and after 4pm, with fines of $220 for individuals, so the running comparison against a natural lawn is a real one. It just is not subsidised.

Related reading

• Synthetic turf in Manly, where ten soil landscapes meet
• Chatswood turf and its split soil profile
• Sydney-wide artificial grass quotes
• Hornsby turf pricing per square metre
• What a Hornsby installation involves, layer by layer
• Turf for dogs on a leafy block
• How to judge synthetic grass quality before you buy
• Artificial grass in Castle Hill
• Artificial grass in Ryde

Soil landscape data: Chapman G.A. and Murphy C.L., 1989, Soil Landscapes of the Sydney 1:100,000 Sheet, Soil Conservation Service of NSW (Map Ed. 4, 2009), NSW Department of Climate Change, Energy, the Environment and Water. Percentages describe the whole suburb polygon, not any individual property.