The end of summer means the end of yard care, right? Wrong. Applying a fall pre-emergent treatment is one of the best steps you can take toward a healthy lawn. The gap between the harsh heat of summer and the cool temperature of fall is a critical time to prepare your lawn for both winter and the following spring.
Keep reading to learn more about pre-emergent herbicides and how to apply them or select one of the sections below to understand how to better prepare your lawn this fall.
What are Fall Pre-Emergents?
Pre-emergent herbicides help prevent weeds from growing or sprouting when applied on the lawn prior to the target weed seeds germinating. Depending on where you live, fall pre-emergent applications should be made between August and November.
Winter can bring about certain weeds, also known as winter weeds, in your lawn. Chickweed, clover, poa annua (annual bluegrass), and filaree are all weeds that germinate in the winter and emerge in your lawn between late February and early March. You want to apply the pre-emergent herbicide before the seed germinates and the weed grows. If you already have winter weeds in your lawn, you will use a post-emergent herbicide.
Pre-emergent herbicides for lawns come in both a liquid form, which you would apply with a sprayer, and a granular form, which you would apply with a granular spreader. Pre-emergent granules look like sand.
It is hard to kill weeds once they have germinated. By using a fall pre-emergent herbicide treatment, you can prevent weeds from germinating, saving you time and money later in the year and through the spring.
Pre-emergent herbicide applications are especially helpful if you know you have certain weeds that grow in your yard every spring. It helps to find out what type of weeds you have to determine the best fall pre-emergent treatment. While you will still need to apply a pre-emergent in the spring, the fall weed control is helpful in case spring comes early and the weather warms before you are able to treat in the spring.
When to Apply Fall Pre-Emergents?
Apply a fall pre-emergent herbicide to your yard when your soil temperatures begin cooling toward 70 degrees F. This is typically between August and November depending on your location. Northern areas may reach this window earlier, while southern areas may not reach it until later in the fall. This is true for both cold-season and warm-season grasses.
A good rule of thumb is to start planning in August. Begin watching the soil temperatures in your lawn as summer heat subsides and apply your pre-emergent weed preventer before winter weed seeds have had a chance to germinate.
To get professional level results, use a split application approach. This involves making two pre-emergent applications 6 to 8 weeks apart using a half-rate for each application. Seeds do not all start germinating at the same time, and using a split application helps extend the weed barrier for your lawn.
As soil temperatures begin dipping below 70 degrees F, winter annual weeds like poa Anna, chickweed, henbit and clover start to germinate. To stay ahead of these weeds, it is important to apply your fall pre-emergent herbicides before the soil temperatures drop and the weeds germinate. This ensures the pre-emergent herbicide can create a barrier before any weeds can take root.
Apply your winter weed prevention product before temperatures drop. Contact your local extension office for more detailed information on the local climate and when to apply your fall pre-emergent herbicide treatment. Timing for an effective fall pre-emergent application can depend on a variety of factors including the location of where you live, climate, and the type of weeds you are trying to control.
Be sure the air temperature outside is below 85 degrees during application. If it is warmer than 85 degrees F, the plants will not absorb as much of the herbicide, which could lead to decreased weed control. If you are wondering how late you can treat weeds in the fall, pre-emergent herbicides are only effective if applied before annual grass weeds germinate. While it's best to apply early, putting down a pre-emergent herbicide before temperatures drop can help control winter weeds and set your lawn up for success next spring.
You will also need to follow up with a spring pre-emergent application around February or March, before the weather warms in the spring. This ensures another barrier is in place before summer annual weeds begin germinating in the spring as soil temperatures begin to warm.
How Do I Choose the Best Fall Pre-Emergent Herbicide for My Lawn?
There are plenty of pre-emergent herbicide options available, giving you a wide range to choose from. The best fall weed control for your lawn will depend on your turf type, equipment, and the plants you are combating.
First, you must determine what type of turf grass you have. Most pre-emergent herbicides are labeled for use in certain grasses and not others. A pre-emergent herbicide that will work on zoysia grass may not be the best option for St. Augustine grass, and vice-versa. Once you know the type of lawn you have, you can then narrow down your pre-emergent choice. Be certain to read the label of any weed preventer you are considering using to determine if it is compatible with your grass type.
Next, you can narrow your selection further by knowing which weeds you need to target. As some weeds are better controlled by different fall pre-emergent active ingredients, knowing which weeds you have had or need to prevent will help you narrow down your options to a selective herbicide that is labeled for pre-emergent control of your target weeds.
If you just moved into your home, have not identified which winter weeds your lawn has had previously, or need to target several weeds at once, a selective herbicide for pre-emergent control labeled for a broad spectrum of weeds is a smart choice. Selective herbicides target specific weeds and come in both liquid and granular forms, and in both pre-emergent and post-emergent formulas. Read the label of the selective herbicide to determine if it will cover the weeds commonly found in your lawn if it is labeled as a pre-emergent, and what effect it will have on your lawn.
There are also non-selective pre-emergent herbicides that will prevent the growth of any vegetation where applied. Always read the label to ensure the product you're using is compatible with your grass.
Finally, you can narrow your selection even further by the mode of application. Liquid pre-emergent herbicides are applied with a sprayer and granular pre-emergents are applied with a spreader. Sprayers are also available in backpack form for easy application, while portable spreaders are helpful for hard-to-reach areas of your lawn. Both applications are equally effective, so the choice depends on which pre-emergent application will be compatible with your turf type, the equipment you may already own, and your comfort level.
Common Fall Pre-Emergent Herbicides
There isn't one best fall pre-emergent herbicide for every lawn. The right fall weed preventer depends on your grass type, the weeds you're trying to prevent, your preferred application method (liquid or granular), and how long you want the product to provide residual weed control.
Below are some of the most common fall pre-emergent active ingredients and when they're typically used.
Pendimethalin
Pendimethalin is a broad-spectrum pre-emergent herbicide that helps prevent many annual grassy weeds, including annual bluegrass (poa Annua), as well as broadleaf weeds like chickweed and henbit. It is available in both liquid and granular formulations, making it a popular choice for homeowners and professionals looking for dependable fall weed prevention.
Popular products:
Isoxaben
Isoxaben is an excellent choice when your primary goal is preventing broadleaf winter weeds. It provides effective control of weeds such as chickweed, henbit, clover, and other broadleaf species before they emerge. Isoxaben is commonly used in lawns, landscape beds, and ornamental areas where broadleaf weed prevention is the priority.
Popular products:
Prodiamine
Prodiamine is one of the most popular active ingredients for fall and spring pre-emergent applications because of its long-lasting residual control. It helps prevent many annual grassy weeds, including annual bluegrass (poa Annua), along with selected broadleaf weeds. Its extended residual makes it a great option for homeowners looking for season-long weed prevention with fewer applications.
Popular products:
Dithiopyr
Dithiopyr provides broad-spectrum prevention of many annual grassy and broadleaf weeds. While it's best known for crabgrass prevention, certain dithiopyr products also provide early post-emergent control of young crabgrass, making them especially valuable in spring applications. It can also be used in the fall to help prevent winter annual weeds when applied at the proper time.
Popular products:
Need Help Choosing the Best Fall Pre-Emergent?
If you're unsure which fall pre-emergent herbicide is right for your lawn, our lawn care experts are happy to help. You can also explore the DoMyOwn Turf Box, a customized lawn care program that includes products based on your location, grass type, and lawn size sent directly to your door when you need them.
What Weeds Does a Fall Pre-Emergent Prevent?
A fall pre-emergent herbicide helps prevent many winter annual weeds before they have a chance to germinate and establish in your lawn. Depending on the active ingredient and product you choose, a fall weed preventer can target a wide range of grassy and broadleaf weeds that begin growing in late summer, fall, and early winter.
By stopping these weeds before they emerge, you'll have fewer weeds competing with your turf throughout the winter and a healthier, cleaner lawn when spring arrives. Many homeowners who skip a fall pre-emergent application end up battling weeds in early spring that actually germinated months earlier.
Common Winter Weeds Prevented by Fall Pre-Emergents
Many fall pre-emergent herbicides are labeled to prevent weeds such as:
Grassy Weeds
- Annual bluegrass (poa Annua)
- Annual ryegrass
- Rescuegrass
- Little barley
Broadleaf Weeds
- Chickweed
- Henbit
- Hairy bittercress
- Shepherd's purse
- Common mallow
- Speedwell
- Clover
- Filaree
- Lawn burweed
Because each herbicide is labeled differently, always check the product label to confirm the specific weeds it controls. Some products are designed to provide broad-spectrum control of both grassy and broadleaf weeds, while others are better suited for targeting specific weed types.
How to Apply a Pre-Emergent Herbicide
Pre-emergent herbicides come in two forms: liquid and granular. Learn how to do a fall pre-emergent application in the video below.
How to Apply Liquid Pre-Emergent Herbicides
Liquid pre-emergent herbicides are applied with a sprayer, either a hand pump sprayer or backpack sprayer. To use a liquid pre-emergent:
1. Select the pre-emergent herbicide that is compatible with your grass and the weeds you want to control.
2. Select your choice of sprayer, either a hand pump or backpack sprayer.
3. Read the label of your fall pre-emergent herbicide and add the indicated amount of water and herbicide to your sprayer. Be sure to wear long sleeves, protective goggles, and gloves when mixing and spraying chemicals.
4. Add in a spray indicator dye to your herbicide-water mixture. This dye will temporarily color your grass once it has been sprayed, helping you keep track of what grass has and has not been sprayed during the application process.
5. Shake your water-herbicide-dye mixture thoroughly.
6. Then, you would walk the area of your lawn while spraying your herbicide. Watch the video above for a demonstration of a pre-emergent application.
Products needed for Method 1
How to Apply Granular Pre-Emergent Herbicides
Granular pre-emergents are applied with a broadcast push spreader or portable hand spreader. To apply granular pre-emergents in your lawn:
1. Fill your push spreader or hand spreader with the granular pre-emergent herbicide that will work best for your grass type and the weeds you are trying to control.
2. If using a broadcast push spreader, set the spreader to the setting recommended on the label of the granular herbicide. Then, place the spreader on the grass, directly next to your sidewalk or driveway.
3. Place your spreader guard down so that the granules will only broadcast onto your lawn and not your sidewalk or driveway. Walk the length of your sidewalk or driveway.
4. Once you have finished walking the length of your sidewalk or driveway, position your spreader a few feet away from the first "row" where you walked. Open the spreader guard so that the granules will now be broadcast from both sides of the spreader.
5. Walk the length of your lawn. Make sure your granules reach the tire marks from your first application row.
6. Continue walking back and forth across your lawn in rows to cover your entire lawn in granules.
7. If using a portable hand spreader, walk the length of your lawn while turning the wheel of your spreader. Walk in rows back and forth, ensuring the granule is distributed evenly across your entire lawn.
Learn how to calibrate a spreader in the video below so you can apply granular pre-emergent herbicides to your lawn yourself.
Products needed for Method 2
Will a Fall Pre-Emergent Kill Existing Weeds?
No. A fall pre-emergent herbicide prevents new weeds from germinating but does not kill weeds that are already growing. If weeds have already emerged, you will need a post-emergent herbicide labeled to control those weeds.
A combination of post-emergent and pre-emergent herbicides will control existing weeds while preventing future weed growth.
Should You Use a Fall Pre-Emergent and Post-Emergent Together?
Yes, in many cases. If you already have weeds growing in your lawn, using a fall pre-emergent and post-emergent herbicide together can be one of the most effective ways to achieve both immediate and long-term weed control.
A fall pre-emergent herbicide prevents new winter annual weeds from germinating, but it won't kill weeds that have already emerged. That's where a post-emergent herbicide comes in. It targets actively growing weeds while the pre-emergent creates a protective barrier to stop new weeds from sprouting.
When Should You Use Both?
Consider using both a pre- and post-emergent if:
- You already have visible weeds such as chickweed, henbit, or other winter annuals in your lawn.
- You're applying a fall pre-emergent later in the season after some weeds have already germinated.
- You want to control existing weeds while preventing new weeds from emerging throughout the fall and winter.
How to Apply a Pre-Emergent and Post-Emergent at the Same Time
Many homeowners apply a fall pre-emergent herbicide and a compatible post-emergent herbicide during the same lawn care application. Liquid products may even be tank mixed if both product labels allow it. Before mixing products:
- Verify that both labels permit tank mixing.
- Perform a jar test to confirm the products are compatible.
- Always follow the most restrictive label directions if application instructions differ.
If you're using a granular pre-emergent, you can typically apply a liquid post-emergent separately to control existing weeds, provided the granular product does not already contain a post-emergent herbicide.
Using a fall pre-emergent and post-emergent together helps eliminate weeds that are already present while reducing the number of new weeds you'll have to manage when spring arrives.
Can You Apply a Fall Pre-Emergent and Grass Seed Together?
Generally, no. If you're planning to overseed a cool-season lawn this fall, it's best to wait to apply a fall pre-emergent. Pre-emergent herbicides create a barrier in the soil that prevents seeds from developing roots. While this is effective for stopping winter annual weeds, it can also prevent desirable grass seed from germinating.
If your lawn needs overseeding with tall fescue, Kentucky bluegrass, or perennial ryegrass, focus on establishing the new grass first. For the best results, overseed at least 45 days before your area's first expected frost to give seedlings time to develop before winter. Once the new grass is fully established, you can resume a pre-emergent program according to the product label.
If winter weed prevention is your top priority, apply a fall pre-emergent herbicide before soil temperatures reach the ideal germination range for winter annual weeds and postpone overseeding until a future season. Planning ahead helps ensure you don't sacrifice weed control or successful seed establishment.
One exception: Some herbicides, like containing mesotrione (such as Tenacity Herbicide) can be applied at or near seeding for many cool-season grasses, providing limited pre-emergent weed control while allowing desirable turfgrass seed to establish. Always verify that your grass type and application timing are listed on the product label before use.
Can You Apply Fall Pre-Emergent and Fertilizer Together?
Yes, in many cases. Applying a fall pre-emergent and fertilizer together is a great way to protect your lawn from winter weeds while providing the nutrients it needs heading into cooler weather. Whether you can apply them at the same time depends on your grass type, whether you're overseeding, and the products you're using.
When Should You Apply Both?
For many established lawns, combining a fall pre-emergent herbicide with a fertilizer can:
- Prevent winter annual weeds before they germinate.
- Promote stronger root growth before winter.
- Improve overall lawn health heading into spring.
- Reduce the number of lawn care applications needed.
Can You Mix Fertilizer and Pre-Emergent?
Often, yes. Many liquid fertilizers can be tank mixed with liquid pre-emergent herbicides if both product labels allow it. Before mixing:
- Confirm both labels permit tank mixing.
- Perform a small jar test to check for compatibility.
- Follow the most restrictive label directions if application instructions differ.
If you're using granular products, you can only apply a granular fertilizer and granular pre-emergent at the same time if both products are applied at the same rate per 1,000 square feet. If the application rates differ, simply make two separate applications. The order doesn't matter, and they can be applied back-to-back.
Why Fall Weed Prevention Matters
Many of the weeds that become noticeable in early spring actually germinate during the fall when soil temperatures begin to cool. Once they've emerged, pre-emergent herbicides can no longer prevent them, leaving post-emergent herbicides or manual removal as your primary control options.
Applying the best fall pre-emergent herbicide at the proper time helps:
- Prevent winter annual weeds before they emerge.
- Reduce weed pressure throughout the fall and winter.
- Minimize the need for post-emergent weed control in spring.
- Allow your turfgrass to enter spring with less competition for sunlight, water, and nutrients.
- Build the foundation for a thicker, healthier lawn during the growing season.
A fall pre-emergent is one of the most effective ways to get ahead of winter weeds and make spring lawn care easier. When combined with a spring pre-emergent program, it provides season-long weed prevention that helps keep your lawn looking its best year-round.
Applying fall pre-emergents will save you both time and money. For optimal weed control, both a fall and spring pre-emergent application are necessary. Consult our lawn care schedules for the best time to apply pre-emergents herbicides on your lawn.
Ready to apply a lawn pre-emergent? Shop our selection of pre-emergents and selective herbicides or give us a call at 866-581-7378 for assistance.