Managing Mixed Grass Species in a Cool-Season Lawn

The Challenge of Unwanted Grass Species

An Ohio homeowner had a Kentucky bluegrass lawn contaminated with tall fescue (unsightly) and zoysia (brown most of the year). Manual removal failed as both regrew from roots/rhizomes.

Why Selective Removal Is Nearly Impossible

• All three are perennial grasses with similar growing requirements.
• No herbicide selectively kills tall fescue or zoysia in Kentucky bluegrass.
• Both spread via underground structures (rhizomes/stolons) that survive pulling.

Cultural Management to Favor Bluegrass

• Mow low: 2.0-2.5 inches stresses tall fescue (prefers 3+ inches) and zoysia.
• Fertilize fall-only: Early and late fall feeds bluegrass's natural growth cycle; avoids stimulating warm-season zoysia in summer.
• Accept limitation: This may reduce but won't eliminate the unwanted grasses.

Realistic Options

1. Live with the mix: Many lawns are species blends. Mow at 3 inches for compromise.
2. Spot-treat with glyphosate: Kill patches, reseed with bluegrass. Labor-intensive.
3. Total renovation: Kill all, reseed with pure bluegrass blend. Only sure fix.
4. Embrace zoysia in hot zones: Let it dominate sunny, hot areas where bluegrass struggles.

Key Insight

Grass "weeds" that are other desirable turf species are the hardest to control. Prevention (clean seed, sod) is far easier than correction. If the mix is stable and functional, managing for the dominant species is often the practical choice.