Dawn Redwood Decline from Nutsedge Competition: Mulch and Persistent Herbicide Strategy

Two 7-year-old dawn redwoods; one declining. Nutsedge (Cyperus spp.) infests base; Roundup used annually. Asks how to save the tree.

Competition Mechanism

Nutsedge forms dense mats, stealing water and nutrients. Roundup kills top growth but tubers survive, regenerating. Tree roots can't compete.

Integrated Approach

• Mulch ring: 3-ft radius, 3 inches deep (pine bark, wood chips). Suppresses nutsedge emergence.
• Targeted Roundup: Spot-spray nutsedge only—shield tree trunk with cardboard. Avoid contact with tree bark/roots.
• Repeat: Nutsedge requires 3–5 applications per season as new tubers sprout.
• Pre-emergent: S-metolachlor (Pennant Magnum) in early spring reduces tuber germination—check label for ornamental safety.

Tree Recovery Support

• Deep water (1 inch) weekly during growing season.
• Fertilize: 10-10-10 at 1 lb/inch trunk diameter (spring).
• Inspect for secondary pests (borers, cankers) on stressed tree.

Consistent nutsedge suppression + tree vigor improvement = best chance for recovery. Dawn redwoods are resilient if root zone is freed from competition.