What Can I Plant Around a Septic Tank? A Guide to Landscaping Septic Areas in Australia
There is a special moment in rural home ownership when you look across the backyard and realise a surprisingly large piece of it isn't really a backyard at all.
It's part of your sewage system.
There may be a tank lid sitting proudly in the middle of the lawn. There might be an absorption trench somewhere beyond it. Perhaps you have an aerated wastewater treatment system irrigating an area you'd quite like to turn into a garden. And naturally, once you've looked at it for long enough, the gardener in you starts thinking:
Surely I can plant something there.
You can.
But this is one part of the garden where I'd resist the urge to arrive home from the nursery with six trees, a shovel and an optimistic attitude.
Landscaping around a septic system is less about hiding it and more about understanding how the system uses the soil around it.
Get that right and the area doesn't have to remain an ugly, forgotten patch of grass forever.
Get it badly wrong and the roots of your beautiful new garden may become considerably better acquainted with your wastewater infrastructure than anybody intended.
First, the septic tank isn't necessarily the bit we're worried about
When people talk about “planting around a septic tank”, they're often actually talking about several different parts of an on-site wastewater system.
The tank is where wastewater initially goes. In a traditional septic system, solids settle inside the tank while clarified effluent leaves and moves into an absorption trench or land application area, where the soil and vegetation become part of the disposal process.
Other properties may have an aerated wastewater treatment system (AWTS) that treats wastewater further before distributing treated effluent through surface or subsurface irrigation.
The exact system matters.
A lot.
Because the patch of lawn sitting above an absorption trench has a different job from the garden bed five metres away from the tank.
Lismore City Council explains that in a conventional system, effluent passes from the septic tank into the absorption trench, where it filters through the trench materials and underlying soil. Vegetation — normally grass — growing above the trench then takes up some of the remaining nutrients.
So that slightly boring-looking patch of grass isn't necessarily wasted space.
It's part of the system.
Before planting anything, work out what you've actually got
This would be my first piece of advice.
Don't guess.
If you've bought a property with an existing septic system, find out where the tank, pipes, trenches and land application area actually are and what sort of wastewater system you're dealing with.
Because “we've got a septic tank somewhere over there” isn't quite enough information to design a garden around it.
NSW uses a range of on-site sewage-management systems including traditional septic tanks and absorption trenches, aerated wastewater treatment systems, evapotranspiration beds, mounds and surface or subsurface irrigation areas.
And the rules for your particular system may be contained in its design and your council approval.
So before we get to the fun bit involving plants:
Find the plan. Find the pipes. Find the application area.
Future You will be delighted.
Why are roots such a big deal?
Because roots don't understand property infrastructure.
They understand water, oxygen, nutrients and somewhere to grow.
Wastewater systems can provide a particularly attractive combination of moisture and nutrients, and vigorous roots can interfere with pipes, subsurface irrigation and absorption systems.
That's why current NSW guidance specifically advises against planting large trees and shrubs or plants with invasive roots on effluent application areas.
This doesn't mean you need to fear every root in the garden.
Grass has roots.
Groundcovers have roots.
Sedges have roots.
The distinction is the size, depth and behaviour of the root system and where you're putting it in relation to the wastewater infrastructure.
A tiny groundcover and a mature gum tree are both technically “plants”.
They are not remotely equivalent landscaping decisions.
So what CAN you plant over a septic absorption area?
Here's where the advice gets more interesting than “nothing but grass”.
The NSW Office of Local Government's current Onsite Wastewater Management Guidelines recommend managed lawn for the majority of effluent application areas because it provides high evapotranspiration.
But the same guidelines also state that shrubs, groundcovers, sedges and grasses growing to around 0.5–1 metre can be appropriate in effluent application areas.
That's useful.
It gives us scope to create something more attractive while still respecting what the area needs to do.
But I wouldn't turn that into a universal list of “septic-safe plants”, because that's not how gardening — or wastewater systems — works.
The plant still needs to suit your climate, soil, effluent quality, system type and exact position.
And local requirements matter.
Dungog Shire Council, for example, takes the more conservative approach of recommending grass around absorption fields because larger tree and shrub roots may clog or damage them, while noting that vegetation around irrigation areas needs to tolerate the nutrient and salt conditions associated with wastewater.
So your first authority isn't a Pinterest graphic.
It's the requirements for your system.
Grass is actually doing a job
Grass gets a bad rap from gardeners because it isn't terribly exciting.
But over an effluent application area, boring can be brilliant.
Managed lawn provides a dense, relatively shallow-rooted cover, protects the soil surface and uses water through evapotranspiration. That's why the NSW guidelines continue to recommend lawn as best practice across many effluent application areas.
It also keeps the area accessible and visible.
That's important.
If something begins going wrong with a wastewater system, you want to notice it.
A suspiciously soggy patch, unpleasant smell, unusually lush growth or surface ponding isn't something you want concealed beneath a magnificent jungle of landscaping.
Sometimes the ability to see the ground is a feature.
But if you hate lawn, this gets interesting
This is where I'd start investigating low-growing groundcovers, sedges and grasses, provided they're appropriate for your particular system and local requirements.
And notice I said investigating.
I wouldn't look through our Plant Hub catalogue and start declaring every low plant “septic safe”.
Root behaviour matters.
Tolerance of wastewater conditions matters.
Mature size matters.
And the particular wastewater system matters.
What we can do is narrow the search to plants with characteristics we're interested in: relatively shallow or fibrous root systems, manageable mature growth and tolerance of the site's moisture and nutrient conditions.
Then confirm suitability for the system.
This is exactly the sort of situation where choosing plants by job rather than simply appearance makes gardening much easier.
Sedges deserve a much closer look
After our reed-bed conversation, this is another place where sedges become interesting.
The NSW guidelines specifically include sedges and grasses among vegetation types that can be appropriate within effluent application areas when suitably selected.
That doesn't mean every sedge belongs on every septic field.
But it gives us a useful category to explore.
Sedges can create a completely different landscape from mown lawn. Repeated in groups, they can produce movement, texture and a much more naturalistic effect while keeping the planting relatively low.
And suddenly the septic area doesn't necessarily need to look like the place where the garden stopped.
It can look intentional.
The trick is restraint.
I'd rather see a broad repetition of one or two appropriate plants than fifteen varieties jammed together because we were desperately trying to disguise the fact there's wastewater infrastructure underneath.
What about Lomandra?
This is one I'd treat carefully.
Lomandras immediately spring to mind when Australians think of tough, strappy, fibrous-rooted landscaping plants. We stock plenty of them, and I'd love nothing more than to tell you to cover every septic area in Tanika®, Lime Tuff™ and Tropic Cascade™.
But that's exactly where good horticultural advice needs to beat good marketing.
The question isn't simply whether a plant has fibrous roots.
It's whether the specific cultivar, mature size and root system are appropriate for the particular wastewater system and its infrastructure.
For example, the NSW guidance advises locating effluent application areas at least one metre from the dripline of existing trees and shrubs and recommends keeping large vegetation away from the system.
So I wouldn't give every Lomandra a blanket tick.
Around the broader landscape? Potentially very useful.
Directly over critical wastewater infrastructure? Check the system design and local guidance first.
That's slightly less exciting than “plant this everywhere”.
It's considerably better advice.
Groundcovers could completely change how these areas look
This is perhaps the category I'd be most interested in exploring.
A low groundcover can cover soil without creating the visual bulk of a shrub. It can soften a large area, reduce the amount of mowing and create a garden that feels connected to the surrounding landscape.
Again, species selection is everything.
A plant being labelled “groundcover” tells you its shape.
It doesn't tell you what its roots are going to do.
That's why I wouldn't automatically recommend something like Aussie Rambler™, Yareena™, Purple Fusion™ or Low Horizon™ directly over a septic field simply because they're low-growing plants we sell.
I'd first determine whether that particular plant is appropriate for the wastewater system and growing conditions.
There is a very useful lesson in that.
Low above the ground doesn't automatically mean harmless below it.
Roots don't read plant labels either.
Don't plant a tree on top because you want to hide the tank
Please don't.
A tank lid surrounded by lawn might not win Landscape of the Year, but a large tree planted directly beside your wastewater infrastructure is not the improvement it initially appears to be.
NSW's current guidance recommends planting large trees far enough away from the effluent application area that the distance is equivalent to the tree's expected mature height.
That's a fantastic rule to remember.
A tree expected to become 10 metres tall?
Think approximately 10 metres from the effluent application area, subject of course to your system's specific requirements.
Suddenly that cute little tree in a 140mm pot requires rather more consideration.
Once again:
Buy the mature plant, not the pot.
Can you plant trees downhill from a septic area?
Potentially, and this is where the older NSW Easy Septic Guide provides some interesting advice.
It suggests planting small, shallow-rooted, water-loving trees or shrubs down-slope and away from the trench system where appropriate, because they can use some of the moisture moving through the landscape.
That's very different from planting them on the trench.
Location changes everything.
This is why landscaping around wastewater infrastructure can actually become quite sophisticated.
Perhaps the application area itself remains low and open.
Further away, you introduce taller vegetation.
Then larger shrubs.
Then trees at appropriate distances.
Instead of trying to conceal the entire septic area beneath one giant planting, you create layers around it.
Now we're designing a garden rather than decorating a septic tank.
Don't shade the whole area either
This is something people often overlook.
Vegetation isn't only taking up water through its roots.
Water is also leaving the system through evaporation and plant transpiration.
The NSW guidelines warn that large trees can shade effluent application areas and reduce evaporation, although increased transpiration may sometimes offset part of that effect.
So creating a beautiful shady woodland directly over the application area isn't necessarily clever.
Sunlight can be useful here.
Your wastewater system does not need a rainforest experience.
And don't build over it
This sounds obvious until somebody decides the flat patch above the septic field would be the perfect place for a garden shed.
It isn't.
Structures, pathways, vehicles and other loads can interfere with access and compact the soil or damage the system underneath.
Wollongong City Council specifically advises against installing structures, paths or other features over land application areas, while other NSW councils warn against driving or parking over absorption areas because compaction can damage the soil and infrastructure.
So:
No shed.
No caravan parking.
No entertaining terrace.
No “I'll just put a little concrete slab here”.
Your septic system has already claimed this real estate.
We need to negotiate around it.
Keep stormwater away
Here's one of the most important things you can do that has absolutely nothing to do with plants.
Don't send more water into the area.
The land application area is already dealing with wastewater from the house.
It does not need the roof joining in.
Council guidance consistently recommends directing roof water, driveway runoff and other stormwater away from absorption or application areas. Excess water can saturate the soil and reduce its ability to accept effluent.
If you've got an area that suddenly becomes boggy after rain, don't immediately plant something that loves boggy ground.
First ask why it's boggy.
If the septic area is failing or being overloaded, a tray of wetland plants is not the solution.
That's a wastewater problem wearing a gardening costume.
A permanently soggy septic field is not a free wetland
This deserves its own section because we just wrote an entire article celebrating wet ground.
Context matters.
A naturally wet patch?
Potentially wonderful wetland garden.
A deliberately designed reed bed?
Fantastic.
A septic absorption area that has suddenly become wet, smells unpleasant or has effluent appearing at the surface?
Problem.
NSW guidance identifies surface ponding, runoff of treated wastewater, poor vegetation growth and unusual odours as warning signs that a land application area may not be functioning correctly.
Don't plant around the problem.
Get the system checked.
There are some gardening challenges we can solve with plants.
Raw sewage is not one of them.
What about fruit trees and vegetables?
I wouldn't use the wastewater application area as the veggie patch.
NSW guidance advises against using effluent to water fruit and vegetables, and councils can have specific requirements around wastewater application and human contact.
There's really no need to complicate this.
Grow the tomatoes somewhere else.
Your property has other dirt.
Treated wastewater can change the soil
Here's something genuinely interesting that doesn't get talked about enough.
Wastewater isn't chemically identical to rainwater.
Depending on the system and what comes out of the household, the land application area may receive additional nitrogen, phosphorus, sodium, chloride and other constituents.
Dungog Shire Council specifically notes that plants used around wastewater irrigation areas need to tolerate nutrient-rich wastewater and that some Australian natives may struggle with elevated nutrient levels. It also warns that chloride toxicity can become an issue in some irrigation areas associated with aerated systems.
This is important because there's a tempting assumption:
Australian native + tough plant = perfect septic plant.
Not necessarily.
Some native plants are adapted to very low-nutrient soils.
Give them an environment receiving regular nutrient-rich effluent and they may be considerably less delighted than expected.
Right plant, right place applies underground too.
Should you mulch over a septic application area?
I would be cautious about changing the surface treatment of an application area without checking the system requirements.
Remember that evaporation is part of how many of these areas function.
Covering the surface with impermeable materials is clearly a bad idea, but even substantial changes to vegetation or surface conditions can alter how water behaves.
Managed lawn remains the recommended best-practice surface for many NSW effluent application areas for good reason.
If you want to turn the area into something more garden-like, check what is appropriate for your particular system before covering it with a thick blanket of mulch and assuming you've improved things.
Sometimes leaving well enough alone is excellent landscaping.
Can you mow over an absorption area?
Generally, yes — and regular mowing is commonly recommended where grass is used.
Several NSW councils specifically advise keeping grass on absorption areas mown and maintained.
What you don't want is heavy machinery compacting the soil.
There is an important difference between running a mower over the grass and deciding the septic field is an excellent shortcut for the ute.
The soil is part of the wastewater treatment and disposal system.
Look after it accordingly.
The best septic landscaping may happen around the area, not on it
This is probably the design principle I'd use most often.
Stop trying to turn the actual wastewater area into the hero.
Keep the critical area simple, low, accessible and appropriately planted.
Then make the garden around it beautiful.
Use larger shrubs at safe distances.
Create repeated groups of ornamental grasses or strappy plants around the perimeter where appropriate.
Position taller vegetation where it doesn't interfere with pipes, shade the application area excessively or block maintenance access.
Use a path around the system rather than across it.
Create a focal point somewhere else.
This is a classic garden-design trick.
If you've got something ugly that can't be moved, you don't always need to hide it.
Sometimes you simply need to give the eye something better to look at.
So, what are the best plants around a septic system?
I'm deliberately not giving you a neat list of ten “septic-safe plants”.
Because I don't think that's responsible.
There are too many different wastewater systems, soils, climates and council requirements for one universal list.
Instead, begin with the characteristics.
Over or within the approved effluent application area, managed lawn is the safest default for many systems and is recommended best practice under current NSW guidance. Depending on the system, appropriately selected groundcovers, grasses, sedges and smaller shrubs around 0.5–1 metre may also be suitable.
Avoid large trees, large shrubs and invasive-rooted plants over the application area.
Keep larger vegetation appropriately separated.
Maintain access.
Don't compact the soil.
Keep stormwater away.
And if you're unsure whether a particular plant is suitable, check your wastewater-system documentation or speak to your council/environmental health officer or wastewater professional before planting it.
Then come and choose the plants.
That's the order I'd do it in.
The septic area doesn't have to be ugly
This is the good news.
Living with an on-site wastewater system doesn't mean surrendering half the backyard to a mysterious patch of lawn forever.
It just means the garden has another set of conditions to work with.
And really, that's gardening.
We work around sun.
Shade.
Clay.
Sand.
Wind.
Frost.
Dogs.
Children.
Kangaroos.
The neighbour's enormous gum tree.
Your septic system is simply another thing on the list.
Understand what it needs, respect the infrastructure underneath and design the landscape accordingly.
Because a beautiful garden isn't one where we've forced every square metre to do exactly what we wanted.
It's one where we've understood what each part of the property is already doing — and planted accordingly.
And sometimes the smartest thing you can plant is absolutely nothing with a 10-metre root system.
Looking for low-growing plants for your wastewater area?
Once you've checked the planting requirements for your particular system, browse our groundcovers, grasses and sedges to find plants suited to your climate and growing conditions.