Trees, Roots and Septic Systems

Where roots cause damage

Which trees are the biggest problem

Fast-growing species with aggressive, water-seeking root systems cause the most trouble — willows and poplars are the classic examples, and species that naturally grow in wet ground are generally worth keeping well away.

That said, any large tree close to a septic system is a risk, and the practical rule is about distance rather than species. Roots commonly extend well beyond the visible canopy, and the mature size of the tree matters more than its size when planted.

What to plant over a drain field

• Grass, which is ideal — shallow-rooted, keeps the soil covered, allows air movement.
• Shallow-rooted, non-woody ornamental plants, well away from the laterals.
• Nothing that requires irrigation, since that adds water the soil must absorb.
• No vegetable beds, because of the contact risk with effluent-treated soil.
• No trees or large shrubs.
• No ground cover that requires deep soil preparation.
• Nothing that needs regular digging or replanting.

Mature trees already over the field

This is the common situation, and removing a healthy mature tree is a significant decision that is not always the right one.

What is right is to stop treating it as a non-issue. Tell your contractor the trees are there — it changes what they look for during an inspection. Ask whether root intrusion is visible in the distribution box or the laterals. And factor it in when interpreting field symptoms: a wet area beneath a mature tree has an obvious candidate cause.

• Tell the contractor at every visit that mature trees stand over or near the field.
• Ask specifically whether root intrusion is evident in the distribution box.
• Ask whether the laterals have been assessed for intrusion.
• Do not remove a tree pre-emptively on assumption alone — get the finding first.
• If the tree is removed, be aware that decaying roots leave voids and can cause settlement.
• Consider root barriers only on professional advice; they can create their own problems.
• Never allow stump grinding or root excavation over a field without marking the system.

Root removal is not a permanent fix

Mechanical root cutting and chemical root treatments both exist, and both address the symptom rather than the cause. Roots regrow toward the same water source.

They can be a reasonable interim measure while a longer-term decision is made, but treat them as maintenance rather than repair. The durable solutions are distance, replacing the intruded run, or removing the source.

When landscaping around the system

1. Mark the tank, the distribution box and the field footprint before any work starts.
2. Tell the landscaping crew explicitly where not to dig, drive or plant.
3. Keep machinery off the field entirely.
4. Do not add fill over the field to change grade.
5. Do not install irrigation over the field.
6. Do not install edging, borders or hardscape requiring excavation over the field.
7. Confirm any new planting against the distance rule before it goes in.
8. Photograph the finished layout and add it to your septic records.

Before any landscaping work begins

Most root and excavation damage to septic systems happens during landscaping that had nothing to do with the septic system. Nobody dug through a lateral deliberately.

1. Mark the tank, the distribution box and the field footprint physically before work starts.
2. Show the crew the markers and say plainly where they must not dig, drive or plant.
3. Keep machinery off the field entirely, not just away from the marked lines.
4. Do not add fill over the field to change grade.
5. Do not install irrigation, edging or hardscape requiring excavation over the field.
6. Check any new planting against the mature-height distance rule before it goes in.
7. Never allow stump grinding or root excavation near the system without marking it first.
8. Photograph the finished layout and add it to your septic records.