Controlling Weeds in a Newly Seeded Lawn Without Harming Grass

Identify Weed Type First

• Grassy weeds (crabgrass, foxtail, annual bluegrass): Look like grass. Hard to control selectively in new seeding.
• Broadleaf weeds (dandelion, clover, chickweed, thistle): Distinct leaves. Selective control possible.

If Broadleaf Weeds Dominate

1. Wait until new grass has been mowed 3–4 times (≈6–8 weeks old).
2. Apply selective broadleaf herbicide (e.g., Weed-B-Gon, Trimec) per label.
3. Spot-spray to minimize chemical use.
4. Or hand-pull—most effective for small areas.

If Grassy Weeds Dominate

No safe selective post-emergent for most grassy weeds in cool-season turf. Options:

• Hand-pull before seed set.
• Overseed heavily in fall to crowd out.
• Accept some weeds; manage with culture.

Roundup (Glyphosate) Warning

Non-selective—kills everything. Only use for total renovation. Shield desirable grass if spot-treating.

Prevention for Next Seeding

• Use clean, certified seed (0% weed seed).
• Prepare seedbed 2–3 weeks early; water to germinate weeds, then kill with non-selective or till.
• Apply pre-emergent (siduron/Tupersan) at seeding if crabgrass history—only product safe with new grass.

Key Principle

Dense, healthy grass is the best weed control. Focus on culture: mow high, water deep, fertilize appropriately, aerate annually.