Tree roots in a septic system are one of the most common causes of blocked drains and absorption trench failure on acreage properties across the Hastings. If you’re seeing slow drains, gurgling toilets or suspiciously green strips of lawn above your trench lines, tree root intrusion is high on the list of suspects. Our septic inspections use CCTV cameras to confirm root presence before any remediation work begins.
How roots actually enter a septic system
Roots don’t punch through intact concrete or plastic. They find their way in through joints that have moved slightly over time, hairline cracks in older concrete pipes, or poorly sealed inlet and outlet baffles on the tank itself. Even a gap of a few millimetres is enough: roots follow moisture and nutrients, and the warm, nutrient-rich flow inside a septic pipe is exactly what they’re looking for.
Absorption trenches are particularly vulnerable because the entire point of a trench is to allow liquid to move into the surrounding soil. Roots interpret the moist trench aggregate as an invitation, grow into the perforated pipe, and eventually block the flow of effluent. Over time, a dense root mat forms inside the pipe and begins holding solids, accelerating the failure.
Older concrete pipes with rubber ring joints are far more susceptible than modern PVC with solvent-welded joints, which is why root intrusion tends to show up on properties built before the 1990s.
The warning signs above ground
The above-ground symptoms of root intrusion often look identical to a full septic tank or a venting problem, which makes remote diagnosis unreliable. Common signs include:
- Toilets, showers and sinks draining more slowly than usual, especially when multiple fixtures run at once
- Gurgling or bubbling from drains after flushing
- Unusually lush, fast-growing grass in a narrow strip over the trench line (roots carrying nutrients to the surface)
- Occasional sewage smell from fixtures or the yard
- Wet or soft ground above the trench after dry weather, suggesting effluent is surfacing because flow is blocked
If these symptoms appear suddenly after a tank pump-out in the last 12 months, the tank itself is unlikely to be the issue. Slow escalation over months more often points to root or trench problems.
What a CCTV drain camera reveals
A CCTV drain inspection is the only reliable way to confirm root intrusion and understand its extent. The camera travels the pipe from the inspection point and shows:
- Whether roots have entered at a joint, a crack, or a broken section of pipe
- How far roots extend into the pipe and whether they form a partial or complete blockage
- The condition of the pipe itself (whether cutting roots will leave a structurally sound pipe behind, or whether the pipe needs relining or replacement)
- Any other defects in the same run, such as pipe belly (low spots that collect solids)
Our septic inspection service can combine a CCTV camera inspection with a general system review so you get a full picture before spending money on any remediation.
Mechanical cutting versus root-inhibiting treatments
Once roots are confirmed, there are two broad approaches: cutting them out mechanically, or using chemical treatments to suppress regrowth.
Mechanical cutting (jet rodding) uses a high-pressure jetter with a rotating cutting head to clear the root mass from inside the pipe. Our septic tank cleaning team can jet blocked inlet lines and trench distribution pipes. Jetting restores immediate flow but does not kill the root system, roots regrow, typically within 12 to 24 months depending on the species and season.
Root-inhibiting treatments (usually copper sulphate compounds or dichlobenil-based foams) are applied inside the pipe to suppress regrowth. These are slower-acting and less effective in systems with high water flow. It is important to note that any chemical use near absorption trenches comes with environmental restrictions in NSW. Chemicals can leach into surrounding soil and groundwater, particularly on blocks close to waterways, wetlands or bores. A licensed operator should assess whether chemical treatment is appropriate for your site before any application.
Permanent resolution almost always requires addressing the source: removing or root-pruning the offending tree, relining the damaged section of pipe with an epoxy sleeve, or replacing the affected trench run. Jetting and chemical treatment are management tools, not permanent fixes.
Trees you should not plant near a septic system
The species most commonly found causing problems on Mid North Coast properties are the ones with aggressive, moisture-seeking root systems:
- Eucalyptus (gum trees): Enormous root spread, very high water uptake. Common on rural Hastings blocks and a frequent offender in trench systems.
- Camphor laurel: A declared weed in many NSW councils. Fast-growing with extensive surface and subsurface roots.
- Willow (Salix species): Well-known for following water sources. Any willow within 20-30 metres of a trench should be considered a risk.
- Poplar (Populus species): Similar moisture-seeking behaviour to willows.
- Large fig trees: Not native but widely planted as shade trees; surface roots are highly invasive.
As a general guide, the safe planting distance for large trees is at least 1.5 to 2 times the expected mature canopy radius from any trench or tank. For smaller shrubs with non-aggressive roots, closer planting is generally acceptable, but check with a landscaper familiar with septic setbacks.
Grass, native groundcovers and small herbaceous plants are fine above and around a trench area; they can actually help manage moisture around the system without causing pipe damage.
| Tree type | Root risk | Recommended minimum setback |
|---|---|---|
| Eucalypts (large) | Very high | 10 m from tank, 15 m from trenches |
| Willow, poplar | Very high | 20 m from any system component |
| Camphor laurel | High | 10 m minimum |
| Ornamental figs | High | 8-10 m |
| Native shrubs (small) | Low | 2-3 m |
| Grass, groundcovers | Negligible | No restriction |
These are indicative distances only. Block size, soil type and root barriers all affect the real risk. Consult a plumber or landscape professional if you’re unsure about an existing tree’s proximity to your system.
Root intrusion FAQs
How do I know if roots are in my septic system and not just a blocked pipe?
Persistent slow draining across multiple fixtures (not just one sink or toilet) combined with gurgling sounds is the key pattern. A single slow fixture is more likely a localised clog. Whole-system slowness, especially with a history of established trees on the block, warrants a CCTV drain inspection to confirm.
Can I pour copper sulphate down the toilet to kill roots?
Copper sulphate crystals have been used as a root suppressant in drains for decades, but there are important limits. The NSW EPA and council guidelines restrict chemical use near absorption trenches because of groundwater contamination risk. Never apply chemicals without first getting advice from a licensed operator who knows your site’s environmental context.
Will jetting fix the problem permanently?
No. Mechanical jetting clears the current blockage and restores flow, but the root system itself remains in the surrounding soil. Without removing the tree or relining/replacing the damaged pipe, roots typically regrow within one to two years. Jetting is a maintenance measure, not a permanent repair.
Do I need council approval to replace a damaged pipe run?
Any work that involves altering a component of your on-site sewage management system, including replacing a section of inlet or distribution pipe, is plumbing work that requires a licensed plumber. Depending on the scope, it may also require a Section 68 approval amendment. Your plumber can advise what notification is needed.
What is the cheapest option if roots have destroyed part of my absorption trench?
Pipe relining (epoxy lining inside the existing pipe) can sometimes rehabilitate a cracked or root-damaged inlet run at lower cost than full excavation and pipe replacement. However, relining is not suitable for a trench distribution pipe that is crushed or collapsed. A CCTV inspection is the only way to determine which option is viable.
Related reading
- Signs your septic tank is full
- Gurgling drains on a septic system
- Septic smell inside the house
- How a septic system works
- Finding your septic tank lid
- Septic tank cleaning service
- Septic inspections