How to Prevent Weeds from Growing in Your Lawn

According to an Extension weed specialist, proper lawn care management and healthy turfgrass are the best ways to prevent weeds from growing in your lawn.

Good lawn maintenance practices such as proper mowing, watering, aeration, and fertilization keep grass thick and healthy, one of the best deterrents against weeds. We’ll share expert tips to explain how to prevent weeds from growing in your lawn.

Before we begin, let’s define our term: What is a weed? A weed is any plant that grows where you don’t want it to. Now, let’s get started.

Use Proper Mowing Techniques

Mow on the Tall Side

Proper mowing is one of the easiest ways to maintain a healthy lawn and prevent lawn weeds. “[Weed] management should focus on creating an environment that favors the lawn and other desirable plants in the landscape, not the weeds,” explains Dr. Leslie Beck, Extension Weed Specialist and Associate Professor at New Mexico State University.

Cut your grass to the recommended mowing height for its type, but mow on the high side of its ideal range. This helps shade the soil and deter weed seeds from germinating. Beck says that the typical mowing recommendation for residential lawns is to keep the grass trimmed at a height of roughly 3 to 4 inches.

But keep this in mind: “Mowing height and especially frequency should be adjusted for the type of turfgrass, the time of the season, and lawn usage in order to maintain a healthy and competitive turf,” instructs Beck. Check out the finer points of mowing in our comprehensive guide: Lawn Mowing Tips: How to Mow a Lawn the Right Way.

Tip: If you set the mower blade too short or have an uneven lawn, the mower may scalp the grass, cutting off parts of the grass plant below the leaves. This opens up the soil to sunlight, creating an ideal environment for weed seeds to germinate. So, err on the tall side when you mow.

Use the One-Third Rule

Using the 1/3 Rule means you should trim no more than a third of the grass blades when you mow your lawn. When you cut your grass too short, it can scalp your lawn. Also, mowing too aggressively can overstress and weaken the grass temporarily, making it more susceptible to weeds.

Tip: Cutting only 1/3 of the grass isn’t the only thing you can do to promote your lawn’s health as you mow: “Keeping sharp mowing blades is…another great option to prevent turfgrass stress and to help reduce open wound areas on the blade where turfgrass diseases can enter,” says Beck.

See Related: How to Sharpen Lawn Mower Blades

Water Strategically

Improper watering leaves turfgrasses vulnerable to weeds: 

• Too little water leaves your lawn thirsty and weak.
• Overwatering your lawn puts stress on your grass and discourages root development. 

“The vast majority of the time, lawns are overwatered,” Beck says, noting that it is important for homeowners to irrigate according to their lawn’s needs rather than having a “set-it-and-forget-it” approach to watering the lawn.

The key to good watering practices is to water deeply and infrequently to encourage deep root growth. Aim for 1 to 1.5 inches of water per week, including rain.

See Related: How Often Should I Water My Lawn?

Take Regular Soil Tests and Add Amendments

Think of your soil as the foundation of your lawn’s health: The right balance of macronutrients — nitrogen, phosphorus, and potassium — and an ideal soil pH, between 6 and 7, create the ideal conditions for a healthy lawn.

“A lawn that is stressed is the most susceptible to weed invasion,” says Beck. “If the turf cannot outcompete germinating weed seedlings by taking up adequate space, water, nutrients, light, etc., then the environment favors the weed and not the lawn.”

Test your soil’s pH and nutrient levels every three years. If you see your grass struggling, you can test it more often. If your test results show an imbalance in your soil’s pH levels, apply amendments and nutrients as needed to boost your soil’s health to help your grass grow strong and resilient.

See Related:

• How to Test the Soil pH of Your Lawn
• What are the Different Types of Soil Amendments for Turfgrass Lawns?
• Fertilizer Numbers: What They Mean and How to Use Them

Apply Pre-Emergent Herbicide

Most homeowners would agree that the best kind of weed prevention is to stop weeds from popping up in your yard in the first place. If you want to be proactive, use a pre-emergent herbicide to kill weeds before they germinate above the soil.

Pre-emergent herbicides work by covering your lawn with a preventive chemical barrier. This barrier disrupts weed growth and kills them before they have a chance to sprout above the surface. 

For optimal results, you must know when to apply pre-emergent herbicides in your yard:

• For warm-season weeds, apply your herbicide in late winter to early spring when the soil temperature reaches 50-55 degrees Fahrenheit.
• For winter weeds, apply the herbicide in late summer to early fall when the soil temperature falls to 70 degrees Fahrenheit. 

Timing is everything with pre-emergent herbicides. Make sure you apply pre-emergent herbicides before germination begins to prevent weeds from growing in your grass. Otherwise, they won’t work, and you’ll have to apply post-emergent herbicides instead.

See Related:

• What Are Pre-Emergent Herbicides?
• How to Apply Pre-Emergent Herbicides
• Best Pre-Emergent Herbicides for Lawns [Reviews]

Dethatch As Needed

Another way to keep weeds from growing is to regularly dethatch your yard. When you start noticing signs your lawn has too much thatch, remove the excess thatch from your lawn.

A little thatch is good for your grass, but too much, usually over 1/2 inch, weakens your lawn and can make it unhealthy and prone to diseases or pests. And those pests include weeds.

When to Dethatch

The best time to dethatch your lawn “is during the mid-to-late spring or early fall when the turf is actively growing and can recover from injury better,” advises Beck. But only a few turfgrass species produce enough thatch to need annual dethatching.

Dethatching by Turfgrass Type

“Turfgrasses that spread by rhizomes and/or stolons such as Bermudagrass, Kentucky bluegrass, or creeping bentgrass will produce more thatch,” she notes. “These types of lawns may need to be dethatched yearly for optimum weed control.”

But grasses that spread by tillers “such as tall fescue and perennial ryegrass don’t produce as much thatch and usually don’t require [de]thatching more than every few years,” she says.

Note: Zoysia and St. Augustine also produce significant levels of thatch, so check the thatch layer yearly if you have either of these warm-season grasses.

See Related: 

• How to Dethatch Your Lawn

Aerate Compacted Soil

Aerate your lawn to keep weeds away. Aeration reduces soil compaction and improves airflow to grass roots. This makes the grass thicker and stronger, which helps to outcompete weeds. But as with all lawn care tasks, timing matters.

“Grasses should be aerated at a time when they are actively growing and can recover from the aeration more effectively,” says Beck. 

Here is Beck’s suggested timing for aeration:

• Cool-season grasses are best aerated in the early spring and/or mid-fall. 
• Warm-season grasses should be aerated during late spring to early summer.

Keep in mind that when and how often you aerate also depends on your lawn. Lawns with clay soil and a lot of foot traffic may need aerating twice a year, while grass in sandy soil with little foot traffic might need aeration only every five years. 

See Related: 

• Guide to Growing Warm-Season Grasses
• Guide to Growing Cool-Season Grasses

Overseed Bare Patches

A healthy yard of thick grass is one of the best methods homeowners can use to keep unwanted weeds out of their yard. Dense grass shades the ground, limiting the amount of sunlight to the earth below, which stops weed seeds from germinating.

“Overseeding bare soil areas in the lawn during the spring and/or fall (depending on [the] type of turfgrass) is a great way to try and get healthy growing turfgrass throughout the growing season to outcompete weeds,” says Beck. 

Yards that are patchy with bare spots or yellowing grass are more prone to weed invasions. If your yard looks a little scraggly, try overseeding to fill in the bare spots.

Pro Tip: If you’ve recently overseeded patches in your turf, heed this advice from Beck: “Caution should be utilized when using herbicides to control weeds in…areas that have been overseeded to avoid injury to newly germinating and young turfgrass.” She continues, “The turf should have at least one growing season to effectively establish prior to making any herbicide application for weeds.” 

See Related: 

• How to Overseed a Lawn in 8 Simple Steps

Fertilize Your Grass

To keep weeds away, fertilize the lawn for full, dense growth. Start by testing your soil to see what nutrients it needs. Then, choose the right fertilizer for your lawn and get started.

Before you begin, a note of caution: It’s tempting, but don’t overfertilize your lawn. This can cause the grass to grow too fast, making it weak and more likely to be taken over by weeds. Follow the results of your soil test for the best results. 

Also, knowing when to fertilize your lawn is critical:

• Fertilize cool-season grasses in early fall or early spring. 
• Fertilize warm-season grasses in late spring or early summer.

When done correctly, fertilizer gives your lawn a boost and contributes to its long-term health. Thick, lush grass is not only pleasant underfoot, but it also crowds out weeds, leaving them no room to grow.

Pro Tip: When choosing a fertilizer, Beck emphasizes that homeowners should “avoid the use of weed n’ feeds, where the herbicide is combined with a fertilizer.” Why? Once again, it’s about timing: Fertilizer and herbicides often need to be applied at different times. 

She notes that herbicides, not fertilizer, should be applied in early spring, before the turfgrass is actively growing. But later in the season, during the fertilization window, the weeds may be too old for the herbicides to work optimally.

She concludes: “Thus, it is safer and you get more bang for your buck to buy a fertilizer and an herbicide and use them both at the most appropriate timing for the target plants.”

See Related: How to Fertilize Your Lawn

Mulch as you Mow

To stop weeds from growing in your lawn, leave the grass clippings as you mow. This natural mulch covers the soil and blocks the sunlight, which is an effective way to prevent many weeds, like crabgrass, from germinating.

In the fall, you can also mulch your leaves, creating an additional layer of fine mulch to block winter weed germination, improve soil health, and protect the lawn before winter. But you may need to mow more often, depending on how many trees you have. 

Here’s a good rule of thumb: Mow when the leaves cover no more than half of the lawn. If the leaf cover exceeds about 50%, mulching the leaves could smother the grass instead, which can lead to lawn diseases.

See Related: 

• Best Mulching Lawn Mowers [Reviews]
• How to Improve Your Lawn With Mulch
• Mulching vs. Bagging Grass Clippings

Choose the Right Grass

When it comes to weed management in lawns, Beck explains that it’s important to choose the right grass for your specific landscape, which will depend on your yard’s sun/shade exposure and soil type, as well as your geographic location and local climate conditions.

• In the warm southern states, heat-tolerant warm-season turfgrasses such as Bermuda, Zoysia, centipede, or St. Augustine works well. If you live in a drought-prone area, choose grasses that are drought-tolerant, like Bermuda, bahia, or buffalograss.
• In the cooler northern states, cool-season grasses like Kentucky bluegrass, tall and fine fescues, and perennial ryegrass, or a cool-season mixture, are common in home lawns.

“If residents need information on what turfgrass might be better for their location and needs, they can contact their local County Extension agent,” suggests Beck.

Hand-Pull Weeds

One of the best ways to get rid of weeds in your lawn is the old-fashioned method of pulling them out. Why? Once they mature, weeds in your yard sow seeds that spread throughout your yard. So, a handful of weeds this year may be an army of weeds a year from now.

Also, certain weeds such as crabgrass or knotweed are aggressive spreaders, so pull them up as quickly as you can to prevent a weed infestation.

My Tip: While you can use a garden trowel to dig up weeds, in my experience, the easiest way to pull up a weed is to use a screwdriver to dig it up by the roots. 

FAQ About Weed Prevention

Tired of a Weed-Infested Yard?

To prevent weeds effectively, it is imperative to take good care of your grass. Proper mowing, watering, aeration, and dethatching are all things you can do to keep your lawn healthy, happy, and most importantly of all, weed-free.

If you are tired of dealing with the weeds in your yard or want to apply pre-emergent herbicides before it’s too late, turn to a lawn treatment company in your area. Let them tackle these unwanted invaders so you can enjoy more grass and fewer weeds throughout the year.

Read More:

• How to Get Rid of Weeds in Flower Beds
• How to Remove Weeds From Gravel (7 Methods)
• Organic Herbicides: A Comprehensive Guide

Main Photo Credit: Lupin / Wikimedia Commons / CC BY-SA 3.0