What to Plant Over a Septic Drain Field (and What to Keep Away)

A septic drain field only works while the soil and the plants above it keep taking the water. Most failures trace back to a tank that has not been pumped out, so solids clog the trench, or to too much water arriving at once. Roots in the pipes, shade and compaction make it worse. For the area itself the guidelines agree on the starting point: keep it in mown grass, in as much sun and wind as the site allows, and keep large trees well away.

This guide gathers what Australian regulators publish on the subject: the NSW Office of Local Government's 2025 Onsite Wastewater Management Guidelines, EPA Victoria's 2024 guidelines, the Queensland Plumbing and Wastewater Code, WA Health, council pages from New South Wales and Western Australia, and the older NSW Easy Septic Guide. It summarises their advice and is not a substitute for it. The council is the regulator: it issues the approval, and the conditions on that approval, not a plant guide, govern what may go on the area. Requirements differ by state and council, so ask the installer or the council before anything on an approved area is changed.

Quick facts

Over trenches, beds and mounds	Mown grass. EPA Victoria's table and the Easy Septic Guide give grass only; the NSW guideline also accepts ground covers, sedges and grasses that stay at 0.5 to 1 metre
Irrigation areas	Grass, or gardens of plants and shrubs suited to effluent (EPA Victoria, NSW guideline)
Large trees	A distance equal to their expected mature height away (NSW guideline); small trees 5 metres and large trees over 20 metres in the Easy Septic Guide
Not on the area	Vegetables, fruit, garden beds, paving, sheds, vehicles, stock, stormwater, and extra water from garden sprinklers or hoses
Signs of trouble	Soggy ground or pooling, a rotten-egg smell, a strip of dark green grass, slow drains
Before you change anything	Ask the installer or the council; altering an approved area can need a permit

How a drain field works, and why the plants on it matter

A septic tank settles the solids and passes the liquid on to a land application area. Regulators also call it an effluent application area, a drain field or, after its most common form, absorption trenches: gravel-filled trenches with slotted pipe laid below the surface. Evapotranspiration beds add a layer of sand and topsoil so water is drawn up by capillary action into the root zone of the grass on top. Secondary-treated effluent from an aerated system is usually spread through dripper lines or spray heads over a dedicated irrigation area.

The soil finishes the treatment. Plants, sun and wind pull the water back out, which EPA Victoria calls a vital role, and the NSW guideline says a managed lawn gives a high evapotranspiration rate and is recommended best practice for the majority of areas. The plants above a trench can undo that in three ways.

• Roots. The Queensland code requires a land application area to avoid the likelihood of root penetration into its pipes. A trench is wet, rich soil, and once a slotted pipe fills with roots it stops taking water.
• Shade. Tall vegetation and buildings cut evaporation, so the NSW guideline says the area should sit where sun and wind exposure can be maximised.
• Compaction and sealing. WA Health notes that the weight of a vehicle can damage the system and compact the soil, reducing its ability to absorb effluent. Paving and sheds seal the surface.

What the authorities say about vegetation

• New South Wales. The Office of Local Government's guideline recommends managed lawn for most areas and says shrubs, ground covers, sedges and grasses that grow to 0.5 to 1 metre are appropriate. Large trees and shrubs, and species with invasive roots, should not be planted on the area. Its model approval conditions go further: the area must not be used for garden beds, vegetable gardens or large trees, and must not be used to grow vegetables or fruit for people to eat.
• Victoria. EPA Victoria's effluent dispersal guideline says grass suits most systems and typically gives higher water and nutrient uptake in a residential setting. Its vegetation table gives grass alone for absorption trenches, beds, evapotranspiration systems, wick trenches and mounds, and grass or gardens with plants and shrubs for irrigation systems. Large trees are not recommended, because of root intrusion and the shade of a maturing canopy.
• Queensland. The Plumbing and Wastewater Code sets performance requirements, not a plant list: the area must avoid root penetration and damage from loads placed on it, and its accepted design method is a site and soil evaluation under AS/NZS 1547, the standard the NSW and Victorian documents also refer to.
• Western Australia. WA Health says effluent from an aerated system must go to a dedicated irrigation area planted with salt and nutrient tolerant plants so it does not pool or run off. It says the effluent is unsuitable for vegetable gardens or food crops, that surface irrigation onto lawns and recreation areas needs approval, and that the area cannot be moved or reduced without approval. The Shire of Mundaring names figs, ficus and willows as well known for doing great damage to septic systems.
• The Easy Septic Guide. This NSW booklet from 2000, hosted by Blue Mountains City Council, gives the rules most people know: full sun, grass kept mown with clippings removed, no concrete or pavers, no cars, no grazing, and no flooding the area with sprinklers or hoses. It says to plant only grass near an absorption field, and carries a separate list of plants for wastewater irrigation areas. It also suggests thirsty trees such as poplars and paperbarks planted down-slope and away from the trench. The newer guidelines name no species, but they advise against large trees and invasive roots, and its tree suggestions are out of step with them.

How far away trees should be

The NSW guideline gives the rule of thumb: plant large trees at a distance from the area equivalent to their expected mature height, and site a new area at least a metre outside the drip line of existing trees and shrubs. The Easy Septic Guide is blunter, with small trees at least 5 metres away and large trees more than 20 metres, or the roots will harm the trench. Our own advice is to treat mature height as the minimum, and to go further for the trees water utilities rate as the worst for pipes.

Where roots have already caused a failure, one of the repair options EPA Victoria lists is a root barrier: a trench one metre deep, dug one metre to the side of the area on the tree side and lined with plastic. Our guide to planting near sewer pipes sets out the ratings and distances the water utilities use for pipes themselves.

Soil and climate change the answer

• Heavy clay. Water leaves slowly, so the system leans on evaporation and plant uptake. Full sun and dense grass matter most here. EPA Victoria lists gypsum on clayey soil among the repair options for a failed area, which is a job for a professional and not a home remedy.
• Sand. Water drains fast and can carry nutrients and pathogens towards groundwater, which is why EPA Victoria does not recommend evapotranspiration beds in its sandiest soil categories.
• High rainfall. EPA Victoria calls surface irrigation unsuitable in areas of high or intense rainfall without wet weather storage, and the NSW guideline says much the same. Divert every roof and paddock flow around the area.
• Dry climates. EPA Victoria says evapotranspiration systems suit low rainfall and high evaporation on soils of relatively low permeability. Here the plants do most of the work, so the cover has to stay alive and growing through a hot summer.

What to plant

Over trenches, beds and mounds: lawn

A mown lawn of whatever grass suits your climate is the regulators' first choice, and in Victoria and under the Easy Septic Guide it is the only one for trenches, beds, evapotranspiration systems and mounds. The Easy Septic Guide suggests a mix of summer and winter grasses so something is growing all year. Where a council accepts low ground cover in place of lawn, kidney weed (Dichondra repens) is a flat, shallow rooted option, but it is not named in any of the guidelines, so ask first.

Irrigation areas: plants on the Easy Septic Guide's list

The Easy Septic Guide's plant list, credited to the Australian Plant Society, is for wastewater irrigation areas, not for absorption trenches. The plants below are on it and in our range. Our lomandra care guide and dianella care guide cover spacing and upkeep.

• Native violet (Viola hederacea): listed among the ground covers.
• Common tussock grass (Poa labillardieri): listed among the grasses; takes heavy clay and wet feet.
• Mat-rush (Lomandra): the list names the genus. Check the mature height of the form you choose against the NSW guideline's 0.5 to 1 metre.
• Flax lily (Dianella caerulea): listed among the sedges, grasses and small plants.
• Fan flower (Scaevola) and cut-leaf daisy (Brachyscome): the list names two Scaevola species and Brachyscome as a genus.
• Hop goodenia (Goodenia ovata): on the shrub list at 1 to 1.5 metres, which is taller than the NSW guideline's size for planting on the area, so it belongs on the down-slope margin.

The same booklet adds a warning that applies to this whole list: many Australian natives cannot cope with the sodium, chloride, nitrogen and phosphorus in effluent, and it advises asking a nursery about the plants for your system. Nothing grown on or near the area is for eating.

Margins and down-slope planting: our own suggestions

Wollondilly Shire Council suggests grasses, small trees or small shrubs planted down-slope of the trench to help absorb the water. The plants below are not named in any of the guidelines, and their tolerance of effluent is not established, so keep them to the margins and outside the area itself.

• Creeping boobialla (Myoporum parvifolium) and pigface (Carpobrotus): flat ground covers for dry, sunny margins. Neither likes clay that stays wet.
• Austral bugle (Ajuga australis): for a damp margin in the south-east.
• Kangaroo grass (Themeda): a low form for the drier margins and the reserve area; it dislikes wet feet.
• White correa (Correa alba) and coastal rosemary (Westringia fruticosa): small shrubs for the outer margin. Both grow taller than the NSW guideline's size for planting on the area.

More plants with the same habits are in our Australian natives collection.

What to keep away

• Large trees and invasive roots. The NSW and Victorian guidelines advise against large trees without naming species. Mundaring names figs, ficus and willows. Water utilities rate trees for the damage they do to sewer pipes, and the same roots find a trench: Hunter Water rates camphor laurel, figs, poplars and willows as extreme, and large gums and casuarinas as very high, and Unitywater lists paperbarks, umbrella tree and large lilly pillies among plants not to plant near pipes. We sell paperbarks and gums and think highly of them, but not within a mature height of a trench.
• Bamboo. Hunter Water rates bamboo as a high risk to sewers.
• Fruit trees and anything edible. Treated effluent can still carry pathogens. EPA Victoria says treated wastewater should not contact the edible parts of herbs, fruit or vegetables. WA Health and Wollondilly say effluent must not be used on vegetable gardens or food crops at all, and the NSW model conditions say the area must not be used to grow vegetables or fruit for people to eat.
• Raised beds, soil and mulch piles. The Easy Septic Guide says not to add topsoil over a trench to soak up overflow, or to store soil on it; a raised bed does both and buries the evaporating surface.
• Paving, sheds, patios, fences, playgrounds and service trenches. EPA Victoria lists all of these as things to keep off or away from the area.
• Vehicles and stock. They compact the soil and can crush the pipes. The guidelines suggest a low fence or a planted edge to keep vehicles, stock, pets and children off an irrigation area.
• Extra water. Do not flood a trench area with garden sprinklers or hoses, and do not let roof or driveway water run onto it. The sprinklers or drippers that are part of an aerated system are a different matter and must be left in place.

Getting it right

1. Find the plan. The council should hold the approval and, for newer systems, a site plan showing the trenches, the irrigation area and the reserve area. Mark the whole footprint before you plant anything.
2. Plant straight after installation. Both the NSW and Victorian guidelines say to vegetate the area immediately. EPA Victoria adds a check each quarter that other uses have not crept onto it.
3. Mow and remove the clippings. The NSW guideline says removing trimmings reduces the build-up of mulch and nutrients on the area.
4. Divert surface water. The Easy Septic Guide suggests a bund about 15 centimetres high on the uphill side, longer than the trench area, to turn runoff around it.
5. Rest the trenches. Systems with two leach drains and a diverter should be switched every 12 months, as Mundaring and WA Health advise.
6. Keep the tank on schedule. The intervals differ by state. NSW sources give a pump-out about every three to five years; EPA Victoria says typically every three to eight years depending on tank size; WA Health says about every four years for a household of four. Aerated systems are serviced every three months in NSW and WA, and under the maker's service contract in Victoria.
7. Watch for failure. The Easy Septic Guide's checklist is soggy ground or pools downhill, a rotten-egg smell, unusually dark green grass on or around the area, weeds thriving downhill, and slow or backing-up drains. EPA Victoria adds dead or dying plants around the area. If you see them, do not dig and do not add soil yourself: call a licensed plumber or your system's service agent. In Victoria, owners and occupiers must tell the council if the system shows any sign of failure.

A word of caution

These are summaries of guidelines written for designers and councils, and the main guidelines all say the right answer depends on the site, the soil and the system. Requirements vary by state and by council, and altering an approved land application area, including its size, its location or what sits over it, can need approval or a permit. The Easy Septic Guide's advice is to contact the council's environmental health officer before landscaping around a trench area. Treat any plant list, this one included, as a starting point and not a ruling.

Sources

• NSW Office of Local Government: Onsite Wastewater Management Guidelines (2025): suitable vegetation, tree distances, exposure, model approval conditions.
• The Easy Septic Guide (NSW, 2000, hosted by Blue Mountains City Council): trench dos and don'ts, plant list for irrigation areas.
• EPA Victoria: Guideline for onsite wastewater management (Publication 5001): maintenance, failure signs, root barriers.
• EPA Victoria: Guideline for onsite wastewater effluent dispersal and recycling systems (Publication 5002): vegetation suitability by system type.
• EPA Victoria: Manage an onsite wastewater management system: householder rules and who to call.
• Queensland Plumbing and Wastewater Code (2025): land application area performance, setbacks.
• WA Health: Secondary treatment and aerated wastewater treatment systems: irrigation area planting, no food crops.
• WA Health: Primary treatment systems: septic tanks, leach drains, vehicles.
• Shire of Mundaring: Installing and maintaining an effluent disposal system: invasive roots, resting leach drains.
• Wollondilly Shire Council: Onsite sewage and septic: planting down-slope, failure signs.
• Hunter Water: Planting near sewer pipes and Unitywater: Think before you plant: trees rated for damage to pipes.
• Your Home: Wastewater reuse: septic effluent disposal, raw vegetables.