Tree roots are the most common reason a household sewer blocks. Urban Utilities, the water utility for Brisbane and Ipswich, puts it plainly: tree roots are the number one cause of blockages in sewer pipes. The good news is that the problem is almost entirely about what is planted where. Choose the right plant for the distance you have and the pipe is left alone for decades.
This guide gathers what Australian water utilities publish on the subject, with the plants they name, and sets it out by distance from the pipe. It is a summary of their advice rather than ours, and the sources are linked at the end.
Quick facts
| General rule | Keep trees at least three metres from sewer pipes (Urban Utilities) |
|---|---|
| Directly over a pipe | Grasses, sedges and strappy plants with fibrous roots |
| 1.5 to 3 metres | Small native shrubs |
| More than 3 metres | Small trees with non-aggressive roots |
| Before you dig | Find your pipes first, through Before You Dig Australia and your council or utility |
Why roots go for pipes
Roots follow water and nutrients, and a sewer or water pipe offers both. Urban Utilities notes that some roots are as thin as a strand of hair and can work through the tiniest join between two pipes. Once inside, they catch whatever comes down the line, wet wipes and cooking fats in particular, and the pipe blocks. Clearing the roots is rarely the end of it, because roots often return to the same pipe they were cleared from. Prevention is cheaper than any repair.
Two details are worth knowing. Freshly laid pipes are more attractive than old ones, because roots are drawn to the softer backfilled soil around them. And the plant that matters is the fully grown one, not the one in the pot, so plan around mature size.
What to plant, by distance from the pipe
Unitywater, which serves the Sunshine Coast, Moreton Bay and Noosa, publishes the most practical list we have found, sorted into three distance bands. Garden plants and grasses have fibrous root systems that stay in the upper soil, which is why they sit closest to the pipe.
Directly above, or up to 1.5 metres away
- Blue flax lily (Dianella)
- Spiny-headed mat-rush (Lomandra longifolia). Our lomandra care guide covers planting and upkeep.
- Tall sedge (Carex appressa)
- Common tussock grass (Poa labillardieri)
- Kangaroo grass (Themeda)
- Common hovea
Between 1.5 and 3 metres away
- Dwarf banksia
- Woombye bush (Phebalium woombye)
- Broad-leaved palm lily (Cordyline petiolaris)
- Austral indigo, dogwood, hairy bush pea and sweet wattle
More than 3 metres away
- Blueberry ash (Elaeocarpus reticulatus). See our blueberry ash guide.
- Plum myrtle and peanut tree
Urban Utilities adds three small trees to the recommended side of the ledger: lemon myrtle, tulipwood and native gardenia. Its general advice is to favour slow growing trees and shrubs with non-aggressive root systems, and to avoid tap-rooted plants, whose roots grow straight down.
These lists were written for south east Queensland. The principle travels, but the species may not suit your climate. In Western Australia, Water Corporation publishes a waterwise tree list and notes that waterwise trees tend to have low-invasive root systems. In South Australia, SA Water publishes a tree planting guide for the same purpose. Check the list for where you live.
What to keep well away from pipes
Hunter Water in New South Wales rates plants by the damage they do to sewers. Its ratings are the clearest we have seen.
- Extreme: camphor laurel, fig trees and rubber plants, poplars, willows.
- Very high: coral trees, large gum trees, jacaranda, liquidambar, Norfolk Island and Bunya pines, Illawarra flame tree, casuarinas, white cedar, pine trees, plane trees, pepper tree, elms.
- High: bougainvillea, pampas grass, silky oak, hollies, Norfolk Island hibiscus, privets, magnolias, oleander, Canary Island date palm, bamboos (listed as Phyllostachys, the running bamboos), rhus trees, brush box, wisteria.
Unitywater adds golden cane palm, large lilly pilly species, umbrella tree, poinciana, paperbarks, mango and black bean. Urban Utilities adds bottlebrushes.
We sell several of these, including lilly pillies, magnolias, bottlebrushes and jacarandas, and we say so gladly. They are good plants in the right place. The right place is simply not on top of a pipe. Give them the distance, or choose from the lists above where the pipe runs close.
Before you plant
- Find the pipes. Lodge a free enquiry with Before You Dig Australia, and ask your council for a drainage plan of your block. Some utilities publish maps: SA Water has its Healthy Pipes tool and Unitywater an interactive map. Treat any map as indicative only.
- Measure to the mature plant. Work from the width and height the plant will reach, not the size it arrives at.
- Leave new pipes alone for a while. Avoid planting near freshly laid pipes.
- Consider a root barrier. Urban Utilities suggests one where a tree must go closer than you would like. SA Water is trialling barriers laid two metres deep between problem trees and sewer connections.
- Ask before you commit. Your water utility, a licensed plumber or an arborist can tell you what suits your street and your soil.
A word of caution
Unitywater says of its own list that it is a guide only, is not all inclusive, and carries no guarantee. The same caution belongs on every list here, this page included. Roots respond to soil, water and the condition of the pipe, and an old or cracked pipe will attract roots that a sound one would not. Use these lists to narrow the choice, then check locally.
Sources
- Urban Utilities: Plant smart to protect your pipes
- Unitywater: Think before you plant
- Hunter Water: Planting near sewer pipes
- SA Water: Planting the right tree in the right place
- Water Corporation: Selecting the right tree
If you are ordering these online, read what to do when your plants arrive first. The first two days after delivery matter more than the first two months.
