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Stop Weeds Before They Start with Pre-Emergent Herbicides

Timothy Dahl

By Timothy Dahl
Published February 9, 2023

Pre-emergent herbicides, also known as weed preventers, are a useful tool in your battle against weeds. The best way to fight weeds is to destroy them before they get started. Here’s how and when to use pre-emergents to maintain a healthy and weed-free lawn and garden year-round.

Skill

Beginner

Time

Few Hours

Man spreading pre-emergent herbicide on his lawn.

When to Apply Pre-Emergent for Best Results

A man pouring pre-emergent granules into a lawn spreader.

Timing is everything when applying pre-emergent but as a general rule, apply pre-emergent by season. You’ll need to do this yearly because pre-emergent only remains effective for about three months.

As the timing of seasons can change from year to year, you can also use the ground temperature as a guide when applying pre-emergent. The soil should be between 55 to 70 degrees for pre-emergent to work effectively. Stick a meat probe thermometer in your soil to get an accurate temperature.

The timing for applying pre-emergent can also be determined by your climate, soil condition and weed type. Check with the experts at your local Lowe’s garden center for guidance on specific recommendations for your area.

Preen weed preventer in granule form.

Preen Weed Preventers

A bag of Scotts crabgrass killer.

Crabgrass Killer

A bottle of liquid chickweed killer.

Chickweed Killer

A bag of Preen dandelion weed preventer.

Dandelion Killer

How to Get Rid of Crabgrass

To prevent summer weeds like crabgrass and ragweed, apply pre-emergent in early spring, March to April. Crabgrass is notoriously difficult to remove so remain patient and let the weed preventer do its job. If you see any stragglers, pull them immediately and don’t allow the pulled weeds to sit on your lawn as they can germinate in an untouched area.

How to Kill Chickweed

To thwart winter weeds like chickweed and bluegrass, apply pre-emergent in the early fall, September to November. Chickweeds are edible, so if you plan on consuming them do not use any type of herbicide on your lawn.

How to Prevent Dandelions

Dandelions are the most colorful of weeds, but don’t let their yellow petals fool you as they can take over your lawn in one season. Dandelions can grow year-round, so apply pre-emergent in the fall and spring to catch them all.

How to Apply Pre-Emergent on Your Lawn

A man using a handheld spreader to apply granule pre-emergent herbicide.

Pre-emergent is available in granular and liquid forms. To apply granular pre-emergent, use a hand-held or push spreader to spread it evenly across your lawn. Be careful when spreading pre-emergent around flower beds and gardens as it can damage plants you intend to keep.  

Liquid pre-emergent can be effective against all types of weeds but is particularly potent against crabgrass. Liquid pre-emergent works faster as it goes straight to the weeds and can be applied more directly. Granular pre-emergent requires water to break it down and releases more slowly. You’ll typically find granular to be much less expensive, so unless you are in a rush or your lawn is in a tight space, granular pre-emergent will work just fine.  

To apply liquid pre-emergent, get a garden sprayer and fill it with a mixture of herbicide and water. Check the herbicide label for the proper mixing ratio. A sprayer allows you to pinpoint an exact area for herbicide application, which protects other plants in your yard.

If you already have a spreader or sprayer you use for fertilizer, you can use it for pre-emergent herbicide, too. Just make sure it’s thoroughly cleaned out using a water hose before and after use.

A bag of Roundup weed preventer.

Granular Weed Preventer

A bottle of liquid weed preventer.

Liquid Weed Preventer

A bag of all-purpose weed preventer.

All-Purpose Weed Preventer

When Is Your Lawn Safe to Use After Applying a Herbicide?

A mother and daughter gardening together.

Herbicides are chemicals so always use safety gloves and wear long sleeves when handling them.  

Children and pets should be kept away from a lawn that has been chemically treated for at least 24 to 72 hours. You can also buy a pre-emergent that is safer to use around children and pets, but always reference the label on your herbicide for the recommended timing.                                                                       

Pre-emergent herbicides are an effective weed killer and a valuable tool for preventing weed growth and maintaining a healthy lawn. By applying pre-emergent at the right time of year, you’ll enjoy a weed-free lawn without the annoyance of pulling them.

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