12 Best Pre-Emergent Weed Killers 2020 + Buyer’s Guide & FAQs

If there’s one thing that’s better than killing weeds in your garden – it’s preventing them from appearing in the first place.

That’s why botanical science boffins created products that do exactly that – and if applied correctly, can keep weeds at bay for up to a year.

Pre-emergent weed killers are designed to stop unwanted vegetation before it has a chance to germinate, so it’s possible that you won’t even see weeds rearing their ugly heads for the season.

Because prevention is much better than cure.

Read on to discover the best pre-emergent weed killers and find the one that’s right for you. A full buyer’s guide and FAQ section will follow.

Let’s nip those weeds in the bud.

12 Best Pre-Emergent Weed Killers 2020

Scotts Halts Crabgrass & Grassy Weed Preventer

For the very best in lawn care, you can do a lot worse than Scotts, a household name when it comes to building turf like a putting green. This is their crabgrass and grassy weed preventer, a granular product that you apply over your lawn using a spreader.

It can be applied in the spring to prevent crabgrass and other problem weeds for the season, and it can also be applied in the fall to keep winter weeds at bay.

It’s not affected by weather after application, and a 10 lbs bag will treat an area of up to 5000 square feet. This is probably the best pre-emergent weed killer for Bermuda grass as it won’t harm it if you’re cultivating a Bermuda grass lawn.

Pros

  • Name to trust.
  • Great coverage for the price.
  • Highly rated.
  • Easy to apply.
  • Very effective.

Cons

  • Application timings need to be just right for success.

Conclusion

A popular, tried and trusted product for keeping crabgrass and other grassy weeds away from your lawn for summer and winter. Just make sure you apply strictly according to the instructions for desired results.

If, however, you are not cultivating Bermuda grass, then you may want to read this article on the best weed killers for Bermuda grass.

Roundup Landscape Weed Preventer

As well as making some of the best post-emergent herbicides, the most recognizable weedkiller brand also manufactures a line of weed preventers. This also comes in granular form, but this time designed to be spread around annuals, established flower beds, and around trees and shrubs.

It creates a protective barrier in the soil, so you will be weed-free for up to six months, and you only need to apply it once per year before unwanted foliage has a chance to grow.

Simply apply using the easy-applicator, mulch, and then water to activate to prevent over 40 types of grassy and broadleaf weeds.

Pros

  • Won’t harm desirables.
  • Long-lasting protection.
  • Good coverage.

Cons

  • Can be a chore to spread around larger areas.
  • Reports that the built-in applicator isn’t the best.

Conclusion

Like all pre-emergent weed killers, you need to exhibit a little patience to see if it’s going to do the job, and this Roundup product is no exception. And check out this review if you’re looking for more good weed killers for flower beds.

Preen Garden Weed Preventer

When it comes to pre-emergent weed killers, Preen products were never going to be far away – and now we have two in a row. First up is their standard weed preventer, a 16 lbs tub of granules that comes with a scoop spreader.

Distribute around bedding areas and then water to activate, and keep your garden weed-free for up to three months.

Safe to use in proximity to over 200 species of flowers, vegetables, trees, and shrubs, you’ll have peace of mind applying this even near your edibles. Best of all, it can be applied at any time throughout the season – just so long as you’ve cleared the area of existing weeds beforehand.

Pros

  • Name to trust.
  • Easy to apply.
  • Very highly rated.
  • Good coverage.

Cons

  • Doesn’t last that long – second application might be required.

Conclusion

One of the best pre-emergent weed killers for vegetable gardens, this is safe to use (as directed) just about anywhere – except for your lawn. Also, like all granular weed preventers – they need to dry after first watering to be considered pet safe – so bear that in mind if you have a fur baby that likes to eat stuff.

Preen Granular Garden Weed Preventer

This next Preen entry has all the benefits of the previous product, but this time with the addition of plant food.

As such, it’s the best pre-emergent weed killer for flower beds, as the balanced fertilizer is designed to promote blooms, increase yields for vegetables, and create strong and healthy root systems.

Again, perfectly safe for use around 200 established flowers, vegetables, trees, and shrubs, one application will feed your plants and prevent weeds for up to three months. The 16 lbs tub with applicator scoop covers 2,560 square feet, and it can be used throughout the season for effective results.

Pros

  • Name to trust.
  • Easy to apply.
  • Very highly rated.
  • Good coverage.

Cons

  • Again, a second application might be required to cover the season.

Conclusion

A quality weed preventer and plant food in one handy bucket. Keep weeds at bay while giving your desirable plants the boost they deserve and reap the rewards later in the season.

The Andersons Granular Pre-Emergent Weed Control

Made with .48% of the active ingredient prodiamine, this is a professional turf barricade from the Andersons that is designed to prevent summer annuals from appearing in your prized lawn. This includes crabgrass, goosegrass, and foxtail.

Most effective when applied in spring and prior to soil temperatures reaching 55 degrees, the DG pro formulation allows for more particles per square inch of the chemical, which significantly improves coverage and leads to better control of the weeds.

One of the best pre-emergent weed killers for lawns there is. This is a commercial-grade product for use around the home that won’t let you down.

Pros

  • Highly rated.
  • Excellent coverage.
  • Long-lasting results.
  • Summer and winter protection when applied twice a year.

Cons

  • Conditions must be just right for success.
  • The directions aren’t the best and difficult to read for some.

Conclusion

It might be a bit tricky to figure out the fine print, but once you do, you’ll have a professional turf protector that will last the season if applied at the right time.

Monterey LG 5130 Weed Impede Herbicide

Up next is Monterey’s Weed Impede herbicide, the first pre-emergent product in our review that comes in liquid form.

It’s a surface-applied herbicide used for the control of many annual kinds of grass and broadleaf weeds in ornamental plantings, rock gardens, bulbs, and ground covers.

Just one gallon can treat between 40 and 80 thousand square feet. Best applied with a pump-sprayer and mixed with the right amount of water, this will keep just about anything unwanted from sprouting up wherever it’s applied.

It also contains an orange dye so you can see exactly where you’ve treated – which is a bonus not to be underestimated, and highly useful for improving your accuracy.

Pros

  • Potent formula.
  • Unbeatable coverage.
  • Compatible with post-emergent herbicides.
  • Able to cultivate after application.
  • Long-lasting protection.

Cons

  • It’s on the pricey side.
  • Not safe for use on your turf.

Conclusion

Probably the best pre-emergent weed killer for gravel, this is a top-quality vegetation control from Monterey – if you don’t mind spending a little more for the best results.

Concern Weed Prevention Plus

Concern’s Weed Prevention Plus is an all-natural pre-emergent weed preventer that is safe for use around people and pets, so ideal if you have furry friends or little feet running around.

It prevents weeds while fertilizing your lawn, and one bag can cover up to 1,500 square feet.

Designed to be especially effective against crabgrass and dandelions (the banes of good lawn care), it also adds a lawn food for a healthy turf you can be proud of.

The active ingredient is natural corn gluten, meaning you can avoid those harsher chemicals with this product if you prefer.

Pros

  • Easy to use.
  • Eco-friendly.
  • Non-toxic.
  • Highly rated.
  • Safe for use anywhere in the garden.

Cons

  • Not as potent as stronger products – but that’s the trade-off when it comes to being green.

Conclusion

I’m always a big fan of natural weed preventers, and you can feel at ease to use this anywhere you like to form a protective weed barrier in your garden. Check out this article for more pet safe weed killers to protect the family fur babies, too.

RM43 43% Glyphosate Plus Weed Preventer

You might be wondering what RM43 is doing on this review of pre-emergent weed killers, and that’s because it works as a weed preventer as well as a spot treatment for existing growth. ANY growth – including murdering nettles.

After application, this will keep any area vegetation-free for up to one year, as well as destroying existing weeds in the process. As such, bear in mind it will kill anything green that it comes into contact with, so care should be taken around your desirable blooms.

Still, there’s not much out there that’s as potent or effective for keeping an area barren of plant life should you so choose. One gallon can treat up to 17,297 square feet, so you have a professional herbicide that is ideal if you need to control larger areas.

Pros

  • Very highly rated.
  • Long-lasting protection.
  • Pre and post-emergent.
  • Kills everything.

Cons

  • Kills everything.
  • High glyphosate concentration.

Conclusion

If you want to keep an area of your garden or yard clear of any plant life for up to one year – then look no further.

Tenacity Turf Herbicide

Like the RM43, Tenacity is a pre and post-emergent herbicide – which is why it’s justified its inclusion here. However, that is where the similarities end, as this is a selective herbicide that is safe for use on your turf lawns for getting rid of nuisance weeds only.

Very cost-effective, it’s used for residual control of undesirable plants in turf grasses, and will keep over 46 different broadleaf and grassy weeds away, with an active ingredient that is actually a naturally occurring compound.

Allow your new grass to flourish as Tenacity prevents invasive weeds from choking out your desirable lawn. And check out this article if you prefer to rid your lawn of weeds without harsh chemicals.

Pros

  • Very highly rated.
  • Excellent coverage for the price.
  • Naturally based ingredients.
  • Kills and controls a large variety of lawn weeds.

Cons

  • Not safe for use around desirable plants.
  • The syringe is useless – use a teaspoon when mixing.
  • Initially expensive upfront.

Conclusion

Quite possibly one of the best pre and post-emergent herbicides for your lawn, this works by inhibiting the production of chlorophyll. If you’ve tried everything else, then this might just take your lawn game to the next level, but it might seem a little on the steep side at first.

Quali-Pro Pre-Emergent Herbicide

This is a professional-grade, pre-emergent formula that contains a very high concentration of prodiamine at 65%.

Effective when used around nurseries, landscaping, turf lawns, and trees and shrubs, it’s this kind of product that the pros use when maintaining sports fields such as golf courses and putting greens.

It can be applied in both spring and fall for season-long control and inhibition of crabgrass and broadleaf weeds, and a little goes a very long way with this five-pound bottle.

Best used in a tank sprayer for covering larger areas, Quali-Pro have developed a genuinely effective pre-emergent herbicide with this formula.

Pros

  • Highly rated.
  • Commercial-grade.
  • Protects against a wide variety of weeds.
  • For use all-around your property.

Cons

  • Can be tricky to figure out quantities for smaller yards and gardens.

Conclusion

With the high concentration of prodiamine, this is one of the most effective, professional weed preventers there is. While it’s more suitable for larger areas, if you want that putting green lawn – then you’ve come to the right place.

Dow Snapshot Pre-Emergent Herbicide

Snapshot is another professional-grade pre-emergent herbicide that is designed for use on desirable lawns and turf grasses. This time it comes in a granular form and can be used to control weeds before they have the chance to emerge.

After application, you can look forward to eight months of a weed-free landscape, as it controls 111 broadleaf weeds and grasses for infringing on your property and choking out desirable plants.

The weeds it is effective against are all listed, and a 50 lbs bag should keep you going for some time.

Pros

  • Commercial-grade product.
  • Can be applied through the season.
  • Very effective.
  • Long-lasting residual performance.

Cons

  • The large bag is difficult to manage.

Conclusion

Another commercial alternative to the named brands, this is a professional pre-emergent weed control option for anyone who has a lot of land to cover. Or, if you simply don’t want to purchase the stuff again for a long time.

Dimension 2EW Dithiopyr Pre-Emergent Herbicide

Our final entry in this review of the best pre-emergent herbicides is this Dimension 2EW product with the active ingredient dithiopyr – a root growth inhibitor.

This specialty, professional-grade herbicide provides pre-emergent and early post-emergent control of crabgrass, as well as 45 other nuisance weedy grasses and broadleafs.

In order to achieve post-emergent control, you should be looking at using two pints of the product per acre. Easily mixed in spray tanks, it’s also compatible with other specialty herbicides for maximum effectiveness and control of a wider range of weeds and is residual in the soil for around four months.

Pros

  • Commercial-grade product.
  • Highly rated.
  • Very effective.

Cons

  • Should only be used on established turf grasses.
  • Surfactant advised.
  • Initially expensive – but value for money in the long run.

Conclusion

A powerful, effective treatment for preventing crabgrass and many other unwanted weeds. Take great care to follow the instructions to the letter – as you can and will damage existing grasses if applied incorrectly.

How to Choose the Best Pre-Emergent Weed Killer

Person spraying herbicide on ground

In this next section, you’ll find further information and advice for choosing the right pre-emergent weed killer for you.

How Pre-Emergent Herbicides Work

Pre-emergent herbicides are most often used well before plant life has germinated – either in early spring or late fall.

They work by inhibiting a key enzyme that provides an invisible barrier through which seed growth cannot pass. Effectively, a pre-emergent herbicide neutralizes a plant before it has the chance to germinate.

Some products will also contain a fertilizer to feed desirable plants or an established turfgrass at the same time.

Any seedlings that have big ideas for seeing the light of day will be terminated by this invisible film in the soil, created when a pre-emergent herbicide has been applied correctly and watered to activate.

Quantity/Coverage

How much pre-emergent herbicide you need will obviously be determined by how much land you need to cover.

As mentioned, a pre-emergent herbicide is specifically designed for distribution over a wide area, so getting the coverage you need isn’t that challenging.

Again, just make sure you’re referring to the instructions when mixing liquid formulas – as achieving the right balance of water (and surfactant – if required) can often be the trickiest part of the process.

Liquid or Granules?

Pre-emergent herbicides are available in granular or liquid form.

Granules are much easier to use and usually come with a scoop of some kind to assist with their application.

However, using a dedicated spreader is better if you have a larger area to cover – but they’re always sold separately. If you don’t have access to such a device, I would recommend picking one up second-hand to save a bit of cash.

While granular pre-emergent herbicides are usually cheaper than liquid versions, you’ll get much better coverage with a liquid.

And when it comes to the effectiveness of a pre-emergent – accurate and extensive distribution is key – which is where liquid herbicides excel.

Still, it can be a bit of a challenge to get mixing quantities right – especially if you’re using a surfactant (an additional liquid product that breaks surface tension and improves herbicide absorbency).

And liquids need the right kind of applicator to do the job, usually in the form of a tank or backpack sprayer. This I would recommend purchasing brand new – so you know that no other chemical has been used in it and you’re not risking any kind of cross-contamination.

Once both versions have been applied, you need to add water to activate. This is where liquid has another advantage, in that it will take less hosing or rainfall for the herbicide to begin working its magic in the soil.

Whichever version you choose, diligently read and understand the instructions before use.

Selectivity/Targeted Weeds

When choosing any kind of weed killer or preventer, you need to be aware of its selectivity.

Herbicides can be selective, or non-selective. Selective means that they will only treat certain types of plant life. Non-selective means they will attack anything.

When it comes to pre-emergent herbicides, it’s important to learn what the chemical is going to kill, and what it’s going to leave alone – if anything.

This is particularly true if you want to apply a herbicide to your lawn. You need to make sure it’s not going to harm existing, desirable plants and grasses.

This is where having an understanding of weed types is highly beneficial. Check out the video below for an excellent guide.

Advantages and Disadvantages of Pre-Emergent Herbicides

The Pros

Naturally, as with all such chemicals, a pre-emergent herbicide comes with its pros and cons. Let’s start with the good news.

Pre-emergents stop weeds in their tracks, meaning that with proper application and at the right time, you might not see a single weed in a treated area for the length of the season.

And speaking of time, a good pre-emergent will be effective for up to one year, and no less than three months – depending on quality.

Finally, the coverage square footage of a pre-emergent herbicide is a very attractive proposition for anyone with larger yards and gardens. Applying this solution is usually much easier and faster than a post-emergent weed killer.

Once again – prevention is much better than cure. For more information, have a look at this article on when to apply weed control.

The Cons

Now for the bad news. Post-emergent herbicides are useless on already established weeds and grasses – and you’d be surprised at just how many people get this wrong and complain when it has had no effect.

(There are one or two products that incorporate both types of herbicide, however, and will kill existing weeds and then keep the treated area plant-free. Still, standard pre-emergent weed killers do not kill visible weeds.)

Also, the timing and temperature of applying pre-emergent needs to be just-so – especially for the effective treatment of crabgrass.

If you’re too late or too early in spring or fall then you won’t have effective results. Whichever product you decide to try, make sure you adhere to the directions completely.

Last but certainly not least, pre-emergent weed killers are rarely pet-friendly. It’s highly advisable you keep children and animals inside – at least until the product has been watered into the soil, and has had a chance to dry.

FAQs

What month do you put down pre-emergent?

Always refer to a particular product’s directions (as they can vary from brand to brand) for the best month to apply the formula. By and large, you’ll want to be putting down a pre-emergent in the early spring or fall.

Certain pre-emergents can be applied throughout the season, but for the most part, the barrier should be down before weeds have a chance to grow – so get in early.

It will also depend on what weed you want to target, so again, make sure you know thy enemy before charging into battle.

Choosing the right product and using it at the right time is essential for your success.

What is the best time to apply a pre-emergent weed killer?

Again, it depends on the type of weed you’re looking to control, and the pre-emergent you’re using. Always read the label.

Check out the excellent video below for advice on using a pre-emergent in the spring – which is when most gardeners will be keen to block forthcoming weeds.

What is the best soil temperature for applying a pre-emergent weed killer?

For best results, you should be applying a pre-emergent herbicide BEFORE the soil has been at a temperature of 55 degrees or above for between 36 and 72 hours.

55 degrees is like DEFCON 1. When the soil temperature goes above that number for a sustained period of time, that’s when seeds begin to germinate, weeds start to become a problem, and then you’re at war.

You can use a soil thermometer, or you can contact your local county extension service for agricultural advice and soil readings in your area.

Alternatively, use this excellent soil temperature map and locate your area.

However, you’ll find that the soil will be around this temperature from March to April for the spring application of pre-emergents.

How long does pre-emergent last?

The residual effects of a pre-emergent herbicide will depend on the particular product you’re purchasing.

Generally speaking, you’ll find they last between 3-12 months. Check the label or specifications for further details before adding to the cart.

Can you put down too much pre-emergent?

Yes – and it can be a seriously grave error if you do with potentially disastrous results.

ALWAYS make sure you adhere to the guidelines on the product label – and like any drug or medicine you might take – never exceed the stated dose.

Also, be aware that the misuse of chemicals in and around your home and property can land you in serious trouble with the law. So, be sure to read that label thoroughly.

How soon can I seed after pre-emergent?

Depending on the pre-emergent (some products you won’t be able to seed at all) you should be waiting between 7-10 days before attempting any new work.

Can I put down pre-emergent and fertilizer at the same time?

Yes, and there are products that contain both – particularly in the Preen and Scotts ranges.

Just make sure you water them both down into the soil well.

Should you mow before pre-emergent?

Lawn mower on green grass

You don’t have to, but it is recommended that your lawn isn’t a jungle when you apply a pre-emergent herbicide. You want the product to be watered into the soil, and that will be easier to accomplish if the grass isn’t too high.

Don’t mow your lawn for a few days after application though, so you can allow the stuff to take hold.

Will rain wash away pre-emergent?

No – in fact, quite the opposite.

Unlike a post-emergent weed killer, you want it to rain after you apply a pre-emergent, because it will save you from having to water the area you’ve treated, and activate the herbicide defense barrier in the soil.

Can you put pre-emergent on wet grass?

No. It won’t be as effective.

Apply the herbicide before it’s due to rain on dry grass and soil, and then water it yourself if no rain is forecast.

Should you water after using a pre-emergent?

Yes! That is how you allow the chemical to activate and get to work protecting your soil and preventing weeds from germinating.

It’s best to add around 1/4-inch of water to the treated area once you’ve applied the herbicide.

Does pre-emergent kill existing weeds?

It depends on the product. Certain pre-emergent weed preventers also incorporate post-emergent weed killers – so they’ll kill anything they come into contact with and keep that area totally plant free for the foreseeable future.

However, by and large, pre-emergent herbicides are useless for killing already established weeds – particularly if they’re already visible through the soil or concrete.

Check out this article for the best weed killers for driveways if you need a post-emergent product that will destroy unwanted plant life where it shouldn’t be growing in the first place.

Summary

The world of herbicides is a complex one, and finding the right product and figuring out the right time for application can be a real headache.

I hope this article and review has helped you choose the best pre-emergent weed killer for your garden project, and that you have much success in keeping weeds at bay as a result.

For my lawn, I would choose the Tenacity product, and possibly the Preen Weed Preventer with plant food for around desirable foliage in landscape beds.

Let me know which pre-emergent you would choose and why.

Happy weeding!