Planting Near Sewer Pipes: Knockout Roses OK, Forsythia Risky

The Pipe Situation

PVC sewer line + flexible plastic pipe, 2 feet deep. You want knockout roses and forsythia against the house in central Kentucky.

Root Risk Assessment

• Knockout roses: Shallow, fibrous roots. Low risk to 2-ft-deep pipes. Safe to plant.
• Forsythia: Vigorous, deep, spreading roots. High risk—can crush or infiltrate flexible pipe joints. Do not plant over pipes.

Safer Alternatives for That Spot

• Dwarf spirea (Spiraea japonica cultivars): Shallow roots, spring flowers.
• Dwarf abelia: Evergreen/semi-evergreen, long bloom, non-invasive roots.
• Boxwood (slow-growing, shallow).
• Perennials: Daylilies, sedum, ornamental grasses—roots stay in top 12–18 inches.

Pro Tip

Contact your county extension agent for local pipe-depth codes and plant lists. They know your soil and infrastructure best.

Enjoy your knockouts. Relocate the forsythia 10+ feet from the line.