Stop Crabgrass Before It Starts—Keep Your Lawn Looking Sharp All Summer.

What Makes Crabgrass a Problem?

Crabgrass is a common annual weed that thrives in hot, dry conditions and poor lawn maintenance. Unlike your turfgrass, which grows thick and upright, crabgrass sprawls across the soil surface, stealing space, nutrients, and sunlight. It has wide, light green blades and forms dense mats that outcompete healthy grass.

Once it establishes, it’s aggressive. Each plant can produce up to 150,000 seeds, all of which lie dormant until the next warm spring. That means one neglected season can lead to years of recurring infestations. And because it dies off in fall, it leaves behind bare patches that are easily overtaken by more weeds or erosion.

Crabgrass also degrades the uniform appearance of a lawn. While your turfgrass grows vertically, crabgrass spreads out flat, creating irregular patches and texture changes. It becomes particularly noticeable in the middle of summer when the contrast between healthy turf and crabgrass is sharpest. This visual inconsistency not only lowers curb appeal but also signals poor lawn health.

Controlling it is key to long-term lawn health and appearance.

Why It’s a Big Deal in the Midwest

Midwestern lawns are primarily composed of cool-season grasses like Kentucky bluegrass, fine fescue, and perennial ryegrass. These thrive in the cooler temperatures of spring and fall. But during the hot and humid summers common in Illinois, Indiana, Ohio, and surrounding states, these grasses naturally slow their growth.

Crabgrass takes advantage of this slowdown. It germinates when soil temperatures reach about 13 °C (55 °F), which typically happens in late April to early May in the Midwest. It then grows quickly through June, July, and August, right when cool-season grass struggles.

What makes it worse is the pattern of weather in the Midwest: spring rains followed by summer heat. That combination is ideal for crabgrass, which germinates in moist soil and thrives in scorching conditions. Unlike desirable grasses, crabgrass has no problem surviving on minimal water and in compacted soils.

That gives crabgrass a competitive edge—and makes early prevention essential.

Steps To Effectively Combat Crabgrass

Step 1: Know When to Act

Timing Is Everything

Crabgrass seeds begin to germinate in early spring, once soil temperatures warm to about 13 °C for several days in a row. While air temperature is helpful to monitor, it’s soil temperature that drives germination. This usually aligns with:

• Mid-to-late April in southern Midwest areas like St. Louis
• Late April to early May in northern cities like Chicago and Minneapolis

Use a soil thermometer or refer to online lawn care tools that track regional soil temperatures to get it right. Missing the timing by even a week or two can significantly reduce the effectiveness of your treatment.

Apply pre-emergent about two weeks before this window. Waiting until you see weeds is too late—the barrier has to be in place first.

Tip: Watch Nature’s Cues

Forsythia bushes bloom around the same time crabgrass germinates. When you see bright yellow blooms, it’s a natural signal that it’s time to apply your pre-emergent.

Other indicators include soil thawing, consistent daytime highs above 15 °C, and early lawn mowing. These signs suggest the lawn is waking up—and so is crabgrass.

If you’re unsure, consult a local extension office or lawn care provider who can advise on regional soil temperature trends. This one step can make or break your prevention efforts.

Step 2: Apply a Pre-Emergent Herbicide

What It Does

Pre-emergent herbicides prevent crabgrass seeds from forming roots. They don’t kill existing plants, which is why timing is so important.

These products create a thin barrier in the upper layer of soil. When seeds try to sprout, they absorb the chemical and die before becoming visible.

Pre-emergents don’t remove crabgrass from the lawn—they just stop new seedlings from establishing. That’s why the application window is brief and must be repeated every season.

Product Types

You can find both granular and liquid pre-emergents:

• Granular: Easy to spread using a broadcast or drop spreader. Ideal for large lawns.
• Liquid: Best for spot treatments or small yards. Requires a sprayer.

Both are effective—just make sure to apply evenly and water lightly afterward (around 0.6–1.2 cm) to activate the product.

Common Ingredients to Look For

• Prodiamine: Long-lasting control, often used by professionals
• Dithiopyr: Controls very young crabgrass in addition to prevention
• Pendimethalin: Common in retail products; shorter residual control

Choose a product based on your lawn’s needs, your timing, and how long you want protection. For example, if you want season-long coverage with just one application, Prodiamine may be a better choice than Pendimethalin.

Application Tips

• Calibrate your spreader to avoid overapplying
• Water within 3 days of application
• Don’t aerate your lawn after applying—it breaks the barrier
• Apply in calm weather to avoid drift (especially for liquid formulas)
• Wear gloves and wash hands after handling chemicals

Also, be mindful of nearby plants and garden beds. Many pre-emergents are non-selective and can prevent seed germination in flower beds or vegetable gardens if applied too broadly.

Step 3: Mow Higher and Less Often

Why It Works

Crabgrass seeds need light and warmth to grow. Taller grass blades block the sun from reaching the soil.

By mowing at 7.5 to 10 cm (3 to 4 inches), you create dense turf and shade that helps suppress crabgrass and other weeds. It also encourages deeper roots, making your lawn more drought-tolerant.

Cutting too low stresses your turfgrass, increases water demand, and exposes the soil to light—all of which favor weed establishment. Maintaining height is one of the simplest but most effective anti-weed strategies.

In fact, many lawn professionals consider mowing height the single most underrated factor in weed control. A thicker canopy prevents not only crabgrass but other weeds like clover and dandelions from getting established.

What to Avoid

• Don’t scalp your lawn (cutting below 5 cm)
• Don’t mow more than 1/3 of the blade at once
• Sharpen your mower blades to avoid tearing grass
• Don’t mow when grass is wet—it can cause clumping and uneven cuts

The goal is to keep grass strong enough to outcompete invaders. Consistent mowing at the right height improves turf density and overall lawn resilience.

Step 4: Skip Spring Seeding (Unless You Have To)

Pre-Emergent Kills All Seeds

Most pre-emergents block all seed germination, including grass seed. This is a critical detail many homeowners overlook. Applying pre-emergent and then attempting to seed bare spots will result in little to no grass growth.

What You Can Do

• Plan your seeding for late summer or early fall when conditions are ideal for cool-season grasses.
• If spring seeding is absolutely necessary, use a product containing siduron, which allows grass seed to germinate while still controlling crabgrass. However, siduron is less commonly available and typically more expensive.
• Consider spot-treating weeds instead of using broad pre-emergents if seeding must be done in spring.

Over time, building a thick, healthy turf through fall seeding is one of the best long-term defenses against crabgrass. Spring is better suited for weed control than for establishing new grass.

Step 5: Fertilize Separately from Crabgrass Control

Combo Products: Convenient but Risky

Many retail stores sell “weed and feed” products that combine pre-emergent herbicide and fertilizer. While these can be convenient, they may not offer the best results for Midwest lawns.

Better Timing

Cool-season grasses like those in the Midwest don’t need a heavy dose of nitrogen in early spring. Too much early fertilizer encourages fast top growth with weak roots. This can leave your lawn vulnerable when summer stress hits.

Best Practice

• Apply pre-emergent in mid to late April.
• Wait until late May or early June to fertilize.
• Use a slow-release fertilizer with a balanced nitrogen-phosphorus-potassium (N-P-K) ratio tailored for your grass type.

Separating these two steps allows for better timing, better results, and a healthier lawn in both spring and summer.

Step 6: Water Deeply, Not Frequently

Crabgrass Loves Moist, Compacted Soil

Crabgrass thrives in lawns that are overwatered, especially when watering is shallow and frequent. These conditions create warm, damp soil near the surface—exactly what crabgrass needs to germinate.

Watering Strategy

• Water 2 to 3 times per week, not daily.
• Apply 2.5 to 3.8 cm per session.
• Water early in the morning to reduce evaporation and prevent disease.

Deep watering encourages roots to grow deeper, strengthening turf and increasing drought resistance. This strategy reduces crabgrass pressure and promotes healthy lawn growth.

Step 7: Aerate and Seed in Fall

Timing Matters

Aeration improves soil health by relieving compaction and promoting air and water movement. But doing it in spring after applying pre-emergent breaks the chemical barrier, allowing crabgrass to germinate freely.

Fall Is Ideal

• Cooler temperatures reduce weed pressure.
• Turfgrass grows vigorously in fall.
• You can pair aeration with overseeding and fertilization for maximum benefit.

Schedule fall aeration in late August through mid-September, depending on your local climate. It’s a key part of building a thick lawn that resists crabgrass naturally.

What If Crabgrass Still Shows Up?

Post-Emergent Solutions

If you see crabgrass during summer, it’s too late for pre-emergent. Instead, use a post-emergent herbicide containing quinclorac, which targets crabgrass without harming most cool-season grasses.

Best Practices

• Apply when crabgrass is young (under 4 leaves or <15 cm wide).
• Avoid spraying in high heat (>30 °C).
• Follow label instructions for reapplication if needed.

Mature crabgrass is difficult to kill and may require repeated treatment or physical removal. Often, it’s better to wait until fall and repair the lawn after crabgrass dies off naturally from frost.

Common Mistakes to Avoid

1. Applying pre-emergent too late – The barrier must be in place before seeds germinate.
2. Overwatering – Shallow, frequent watering promotes weeds.
3. Mowing too short – Always maintain 7.5–10 cm mowing height.
4. Seeding too soon after herbicide – Wait 8–12 weeks, or seed in fall.
5. Skipping annual treatments – Crabgrass prevention needs to be repeated yearly.

Midwest Lawn Calendar: Quick Reference

Month	Task
March	Rake leaves, test soil
April	Apply pre-emergent herbicide
May	Mow regularly, fertilize if needed
June	Watch for weed breakthrough
July	Spot treat with post-emergent
August	Plan for aeration + overseeding
September	Aerate, seed, feed
October	Final mow, winterize if needed

Frequently Asked Questions

Q: What temperature does crabgrass die?
A: It dies after the first hard frost in fall, typically around -2 °C.

Q: Can I apply crabgrass preventer in fall?
A: No. Crabgrass is an annual that dies in fall. Apply pre-emergent in spring before germination.

Q: Can I seed and use pre-emergent at the same time?
A: Only with siduron. Most pre-emergents block all seed growth.

Q: What’s the best mowing height to prevent crabgrass?
A: Keep grass at 7.5 to 10 cm (3 to 4 inches) to shade the soil.

Q: How often should I reapply pre-emergent?
A: Every year in spring. Some products require a second application 6–8 weeks later.

Final Thoughts

Crabgrass prevention is all about timing, consistency, and understanding how your lawn responds to seasonal changes. Midwestern lawns face unique challenges, but with a solid plan, you can keep crabgrass out and healthy grass thriving.

Start early with pre-emergent, mow high, water wisely, and focus on fall for repairs. Don’t wait for weeds to take hold—be proactive.

If you’re overwhelmed by the details or need help choosing the right products and schedule, contact a local lawn care service. A professional can tailor treatments to your lawn’s specific needs, helping you stay ahead of crabgrass all season long.

A crabgrass-free lawn isn’t just a pipe dream—it’s a manageable goal with the right steps.