Stopping weeds early—before they can emerge from the soil—is the goal when applying a pre- emergent herbicide. A pre-emergent prevents the sprouting of undesirable weed seeds, so it’s a beneficial partner in the war against weeds in lawns, flowerbeds, and even vegetable gardens.
The best pre-emergent herbicide product will vary, depending on the size of the area requiring treatment and the type of weeds the gardener wants to kill. Ahead, learn what to look for when shopping for a pre-emergent weed killer, and find out why the following products can all help prevent unwanted weeds this year.
- BEST OVERALL: Quali-Pro Prodiamine 65 WDG Pre-Emergent Herbicide
- BEST BANG FOR THE BUCK: Miracle-Gro Garden Weed Preventer
- BEST FOR FLOWERBED: Preen Garden Weed Preventer + Plant Food
- BEST FOR PESTS: Preen Weed Preventer Plus Ant, Flea, & Tick Control
- BEST FOR LAWNS: Scotts Turf Builder Halts Crabgrass Preventer
- BEST NATURAL: Preen Natural Vegetable Garden Weed Preventer
What to Consider When Choosing the Best Pre-Emergent Herbicide
Pre-emergent herbicides are well suited for lawns and gardens where desirable grass and plants are already established. However, gardeners should not apply these products where they plan to plant beneficial seeds, such as starting flowers or vegetables from seeds or overseeding a lawn. These products vary in form, strength, and in the type of ingredients they contain. Many are labeled as “weed preventers.” Read on to discover more about these and other important factors to consider when selecting the best pre-emergent herbicide.
Pre-emergent herbicides are available in two primary forms: liquid and granules. While they both work in the same manner—by preventing weeds from emerging from the ground—groundskeepers and gardeners may prefer applying one form over another. Either type will help reduce the need for manual weeding.
- Liquid: Available either concentrated or full-strength for use in a pump-type sprayer, liquid pre-emergent herbicides are easy to apply and are well suited for treating lawns to protect them from crabgrass and other weeds. Concentrated liquids are the form of choice for many commercial applications, such as golf courses and parks.
- Granules: Granules resemble tiny grains and can be applied by a drop spreader, a broadcast spreader, or simply shaken out of a cup onto the soil to control weeds. The granules dissolve and seep into the soil after watering to form a weed-germination barrier.
Rather than targeting different types of plants, as many post-emergent herbicides do, pre- emergent herbicides target plants in different stages of growth. A pre-emergent will stop a seed from developing roots or a shoot, but it will not harm a larger plant’s roots. Also, a pre-emergent herbicide will not kill the roots of perennial weeds, such as bindweed or witchweed, that may lie beneath the soil. This can be a source of confusion for gardeners who see weeds emerging after the application of a pre-emergent herbicide. To eliminate perennial weeds, it’s best to wait until they emerge from the soil and then treat them directly with a post-emergent herbicide.
While many pre-emergent herbicides will prevent the germination of a majority of seeds, some weed seeds, such as crabgrass, may survive some of the weaker types of pre-emergent herbicides. For this reason, manufacturers often combine two or more of the following types of pre-emergent herbicides in a single product.
- Siduron: Siduron is commonly found in products designed to stop the seeds of weedy annual grasses, such as foxtail and crabgrass, from germinating.
- Trifluralin: Trifluralin is chiefly found in pre-emergent herbicides for use in flower and vegetable gardens as it prevents the germination of a wide variety of seeds.
- Isoxaben: Isoxaben is mainly used in agricultural crops to control broadleaf weeds, such as clover and bindweed.
- Dithiopyr: Dithiopyr is found in many types of pre-emergent lawn products—it controls crabgrass, a common lawn annoyance, in addition to other weeds.
- Pendimethalin: Pendimethalin is the only pre-emergent herbicide that also features some post-emergent properties. It’s used on lawns and agricultural crops, such as cotton and corn.
- Benefin: Benefin is found in herbicides used in vegetable gardens. It’s also useful for preventing grassy weeds in fields of legume-type crops, such as clover and alfalfa.
- Corn gluten: Corn gluten is the only natural pre-emergent herbicide currently on the market. An organic weed killer, it will stop many weed seeds from germinating. If a product contains corn gluten, it probably does not contain any additional chemical herbicides.
Pre-emergent herbicides form a barrier in the soil that stops successful weed seed germination. The average product will protect an area for 1 to 3 months, but some offer even longer control. Many manufacturers recommend applying pre-emergent herbicide products in the spring at about the time forsythia blooms are beginning to fade and then applying once more in early fall to prevent blown-in weed seeds from germinating. While the use of a pre-emergent may not stop all weeds from germinating, it will eliminate the majority of them, even if used only once per year.
Safety and Application
Most pre-emergent herbicide products are safe when used as directed. The key to maximizing safety is planning ahead and applying when children and pets are not around.
- Read the label. Unlike other products that come with safe-use instructions, herbicides bear this warning: “It is a violation of Federal law to use this product in a manner inconsistent with its labeling.” When misused, chemical herbicides can pose a danger to residents of the home, to animals, and to the environment.
- Protect the body. If they are inhaled or make contact with skin, some pre-emergent herbicide products may cause respiratory symptoms or skin irritation. Wear gloves, long sleeves, long pants, a dust mask, and eye protection during application.
- Apply on a calm day. This is more important when applying a liquid spray than granules. Wind can carry the spray, reducing good coverage in the desired area and perhaps contaminating an area where the gardener wants to plant seeds.
- Water after application. If rain isn’t in the immediate forecast, most pre-emergent herbicide products call for watering to encourage the herbicide to seep into the soil and form a barrier against seed germination.
- Wash afterward. Even with care, some of the product may inadvertently land on skin or clothing, so change clothes and thoroughly wash up after application to be on the safe side.
Our Top Picks
To qualify as a top pick, a pre-emergent herbicide should prevent a wide variety of weeds from sprouting and offer easy-to-follow instructions. While the best pre-emergent herbicide will vary depending on the treatment location, such as a lawn or a vegetable garden, it should stop the type of weeds most likely found in those specific areas. All of the following products will reduce hand-weeding and help avoid the need for additional post-emergent treatment of weeds.
Those looking for an effective pre-emergent herbicide to prevent crabgrass in lawns, flowerbeds, and other planted beds and borders need look no further than Quali-Pro Prodiamine 65 WDG Pre-Emergent Herbicide. This professional-quality product is available in a 5-pound granular concentrate. It is designed to dilute and apply with a pump-type sprayer to lawns, under trees, and around bushes and shrubs.
In addition to controlling crabgrass, this pre-emergent controls several other troublesome weeds, including henbit, chickweed, and spurge. Prodiamine is the active ingredient; for the best results, apply the product both in the spring and in the fall.
Reduce weeding tasks without spending a lot of money with the Miracle-Gro Garden Weed Preventer. This granular pre-emergent comes from a well-known manufacturer, and best of all, it’s affordable. Available in a 5-pound jug, the convenient shaker top makes it simple to sprinkle the granules around established plants.
The Miracle-Gro weed preventer works best when applied early in the growing season, and it will prevent weed seeds from germinating for up to 3 months. It can be used in flowerbeds, around shrubs, and in the vegetable garden, but it’s not recommended for controlling weeds in lawns.
Prevent weeds in the rose garden or the poppy patch while boosting plant health. The Preen Garden Weed Preventer + Plant Food creates a barrier in the soil that doesn’t allow weed seeds to germinate, while simultaneously providing nutrients that encourage robust plant growth and large bountiful blooms.
The active ingredient is trifluralin, and it comes in granular form in a hefty 16-pound container—enough to last the average gardener all year. This weed preventer dramatically reduces the number of weeds for up to 3 months, and it includes a handy shaker scoop that allows users to scoop up the granules and then uniformly disperse them on the soil.
Prevent weeds in flowerbeds and perennial borders with Preen Weed Preventer Plus Ant, Flea, and Tick Control. This product is not suitable for lawns or vegetable gardens, but it will stop unwanted weed seeds from sprouting in ornamental beds and around bushes and shrubs for up to 4 months using dithiopyr as the active ingredient.
As an added bonus, this herbicide product contains a pesticide that kills ants, fleas, and disease-carrying ticks. It comes in a 4.25-pound jug with a shaker top to easily dispense the granules. For the best results, sprinkle the product and then thoroughly water the area. Keep pets and children away from the area for 24 hours.
Scotts Turf Builder Halts Crabgrass Preventer stops crabgrass before it can start while protecting the lawn from other weeds for an entire growing season. At the same time, this pre- emergent herbicide feeds the grass to help it develop a deep, healthy root system. The product features pendimethalin as the active herbicide and comes in a 1-pound bag for distribution with a drop spreader or a broadcast spreader.
For the best results, apply this pre-emergent early in the season, soon after the snow thaws, to create a weed-free barrier and a lush lawn. Once applied, it requires thorough watering or at least 0.25 inches of rain within 2 to 3 days.
Those looking for a natural pre-emergent for fruits and vegetables can check out Preen Natural Vegetable Garden Weed Preventer that contains no harsh chemicals, ensuring it’s safe for use around plants that produce foods. Corn gluten is the active ingredient in this pre-emergent, which creates a natural barrier to seed germination and makes it the most eco-friendly of all the herbicides in this lineup.
The product comes in granular form in a 5-pound bag, and it should be applied every 4 to 6 weeks to keep weeds at bay. This natural pre-emergent prevents crabgrass, clover, dandelions, and other weeds.
FAQs About Pre-Emergent Herbicides
Reducing the amount of weeding in a garden or flowerbed is the goal of many gardeners, and applying a pre-emergent herbicide can help. For those new to herbicides, however, some questions are to be expected.
Q. Will pre-emergent herbicide kill crabgrass?
A pre-emergent herbicide will not kill established crabgrass, but it will stop the germination of new crabgrass seeds.
Q. When should I apply pre-emergent herbicide?
For the best results, most pre-emergent herbicides should be applied at least once in the spring and once in the fall. Check the product label for additional instructions.
Q. What is the best temperature to apply pre-emergent herbicide?
Apply a pre-emergent herbicide in the spring when outdoor temperatures are still relatively cool—around the low 50s—before weed seeds begin to germinate.
Q. Will rain wash away my pre-emergent herbicide?
Rain will actually help the pre-emergent herbicide seep into the soil to form a barrier against weed seeds. Only a torrential rain would likely wash away the product.