How Do I Get Rid of Crabgrass?

Crabgrass is one of the most frustrating weeds homeowners deal with in Southeastern Pennsylvania. It spreads aggressively, chokes out healthy turf, and leaves bare patches behind once it dies in fall. Many homeowners try to fight crabgrass after they see it, only to find it keeps coming back every year.

The truth is simple: crabgrass control is mostly about prevention, not reaction. This article explains how crabgrass actually grows, when it can be stopped, and what homeowners in the Main Line and Delaware County need to do to eliminate it long-term, based on turf science and Penn State Extension recommendations.

What Crabgrass Is and Why It’s So Hard to Control

Crabgrass is a summer annual weed. That means it:

• Germinates from seed each spring

• Grows aggressively during summer heat

• Produces thousands of seeds

• Dies with the first frost in fall

The problem is not just the crabgrass you see—it’s the seed bank in the soil. A single crabgrass plant can produce tens of thousands of seeds, which can remain viable for years.

This is why crabgrass often feels “inevitable” when the real issue is missed prevention timing.

The Only Reliable Way to Stop Crabgrass: Pre-Emergent Control

Penn State Extension is very clear on this point: pre-emergent herbicide is the most effective method for crabgrass control.

Pre-emergent works by stopping crabgrass seeds from establishing roots after germination. The seed may sprout, but it cannot survive.

Important facts homeowners need to understand:

• Pre-emergent does not kill existing crabgrass

• Once crabgrass is visible, prevention for that season has already failed

• Timing matters more than product choice

  
  

When Pre-Emergent Must Be Applied in Southeastern PA

Crabgrass germination is driven by soil temperature, not calendar dates.

Penn State research shows crabgrass begins germinating when soil temperatures reach approximately 55°F for several consecutive days.

In Wayne, Devon, Newtown Square, and Broomall, this typically occurs between late March and mid-April, depending on spring weather.

Applying pre-emergent too early reduces effectiveness. Applying it too late allows crabgrass to establish.

Late April - Early May: Second Pre-Emergent Crabgrass Control Will prevent any late crabgrass from growing.

This narrow timing window is why many homeowners miss it.

Why Post-Emergent Crabgrass Control Is Limited

Once crabgrass is visible, pre-emergent is no longer an option. At that point, post-emergent crabgrass control can reduce existing plants, but it has limitations.

Post-emergent crabgrass treatments:

• Are most effective on young, newly emerged crabgrass

• Become less effective as plants mature

• Often require multiple applications

• Do not stop new crabgrass from germinating

Even when post-emergent works, the crabgrass has already competed with your turf for weeks, weakening the lawn and opening space for more weeds later.

This is why relying on post-emergent alone leads to repeat infestations every year.

Why Crabgrass Thrives in Some Lawns and Not Others

Crabgrass doesn’t invade healthy lawns easily. It thrives when turf conditions are weak.

The most common reasons crabgrass takes over include:

• Mowing too short

• Infrequent mowing

• Thin or patchy turf

• Lack of fertilization

• Compacted soil

• Poor summer stress tolerance

Low mowing height is especially problematic. Cutting below 3.5 inches exposes soil to sunlight, which triggers crabgrass germination.

Dense, well-maintained turf naturally suppresses crabgrass by blocking light at the soil surface.

Why “Crabgrass Treatments” Alone Don’t Solve the Problem

Many homeowners assume crabgrass is a chemical problem when it’s actually a system problem.

Even the best pre-emergent will struggle if:

• The turf is thin

• Soil is compacted

• Mowing height is too low

• Fertility is inconsistent

Penn State consistently emphasizes that turf density is the foundation of weed prevention. Pre-emergent works best when combined with proper mowing, fertilization, and soil management.

What a Proper Crabgrass Control Plan Looks Like

For lawns in Southeastern PA, long-term crabgrass control requires:

• Spring pre-emergent applied at correct soil temperatures

• Weekly mowing at 3.5–4.25 inches

• Proper fertilization to maintain turf density

• Avoiding summer scalping

• Spot-treating breakthrough crabgrass when necessary

• Fall overseeding to repair thin areas left behind

When these steps are followed consistently, crabgrass pressure drops dramatically—often within one to two seasons.

Why Crabgrass Keeps Coming Back Every Year

If you battle crabgrass annually, the cause is almost always one of the following:

• Pre-emergent applied too late or skipped entirely

• Lawn cut too short in spring and summer

• Thin turf from poor fertility

• Bare areas never repaired with overseeding

• Overreliance on post-emergent sprays

Crabgrass is predictable. When the system is fixed, the weed problem disappears.

Professional Crabgrass Control Based on Turf Science

Haven Lawn & Landscape builds crabgrass control programs around Penn State Extension research and the specific conditions found in Southeastern Pennsylvania. Our approach focuses on:

• Proper spring pre-emergent timing

• Lawn density improvement through fertilization

• Correct mowing height and weekly schedules

• Preventing summer stress

• Repairing thin areas through overseeding

The goal is not just to kill crabgrass this season but to prevent it from returning year after year.

If you want lasting crabgrass control instead of temporary fixes, a science-based lawn-health program is the most reliable solution.