Post-emergent herbicides kill weeds, like dandelions, that are already cluttering your yard. Unlike pre-emergents that stop seeds from sprouting, these treatments kill active growth. You need to choose a type that destroys your specific weeds without harming your grass or plants.
The main types are systemic (kills the whole plant, including roots), contact (kills only what it touches), selective (targets specific weeds without harming grass), and non-selective (kills everything). Each comes in liquid or granular form with different active ingredients designed for specific weeds.
Handling a severe weed takeover is often a job best left to the pros. Lawn Love’s local experts identify your specific weeds and apply targeted treatments to clear them out safely.
| Key takeaways |
|---|
| • Systemic herbicides work slowly but kill weeds completely, including roots (best for perennial weeds) • Contact herbicides act fast but may require repeat applications (ideal for annual weeds) • Selective herbicides target specific weeds without harming your grass (safest for lawns) • Non-selective herbicides kill everything they touch (use only in driveways, sidewalks, or for total vegetation removal) • Liquid formulas work faster, while granular products last longer and reduce drift |
Systemic vs. contact post-emergent herbicides
You need to know how the herbicide attacks the plant to predict results. This determines if the weed dies completely or just turns brown for a few weeks.
Systemic post-emergent herbicides
Systemic herbicides travel through the leaves down to the roots, killing the weed from the inside out.
Seasoned pro Steve Rice, owner of Lawn Kings in Valencia, CA, prefers systemic products when long-term control matters because they kill the deep root systems of weeds at the source.
“The main downside of this slow-kill approach is patience,” Rice says. “You won’t see results for days, but the upside is fewer repeat applications and less regrowth.”
Tim DiAngelis, owner of Lawn Care Plus, in Roslindale, MA, agrees, pointing out that the 7-to-14-day window can be nerve-wracking for customers.
“I’ve had clients panic at day 5 thinking it didn’t work, then suddenly all their dandelions collapse at once on day 10,” DiAngelis says.
- Best for: Deep-rooted perennial weeds like dandelions, creeping bentgrass, thistle, and ground ivy
- Best applied: Spring or fall when weeds are actively growing and temperatures range between 65–85°F.
- How long it takes: Slow. You will see yellowing in 7-14 days. Complete weed death takes 2-3 weeks.
| Pros: | Cons: |
| ✓ Kills the entire plant including roots ✓ Prevents regrowth of perennial weeds ✓ Works on mature weeds ✓ Available in multiple formulas | ✗ Takes longer to show results ✗ More expensive than contact herbicides ✗ Can drift to nearby plants in liquid form ✗ May persist in soil and affect future plantings |
Contact post-emergent herbicides
Contact herbicides kill only the plant parts they directly touch, causing the leaves to dry out or “burn down” almost immediately. DiAngelis says these products—often containing pelargonic acid—work much faster than systemics, often showing “browning in 24–48 hours.”
While the quick results are impressive, they are often temporary. Rice warns that because these sprays only burn what they hit, they often “leave roots alive and weeds coming back.”
This makes contact herbicides a poor choice for difficult, established weeds. DiAngelis adds that while they work for simple annuals, they are “useless for perennials like creeping Charlie that regrow from roots.”
- Best for: Young annual weeds with shallow roots, like chickweed, clover, and small broadleaf weeds. Great for edging driveways.
- How long it takes: Really fast. You’ll see browning and yellowing in just 2-3 days. The roots might survive and grow back.
- Best applied: When weeds are actively growing and temperatures range between 65–85°F.
| Pros: | Cons: |
| ✓ Fast-acting results ✓ Works great on young, tender annual weeds ✓ Minimal soil residue ✓ Can be combined with systemic herbicides ✓ Perfect for spot-treating problem areas | ✗ Doesn’t kill roots, so weeds may regrow ✗ Requires thorough coverage for effectiveness ✗ May need multiple applications ✗ Less effective on weeds with waxy or hairy leaves ✗ Not a long-term solution |
Read more: Common Broadleaf Weeds Found in Your Yard
Liquid vs. granular post-emergent herbicides
You can apply weed killers as a liquid spray or a solid granule. For killing weeds that are actively growing, liquids are superior.
Liquid post-emergent herbicides
Liquid herbicides are mixed with water and applied using anything from simple spray bottles for spot treatments to backpack or hose-end sprayers for larger areas.
According to Rice, this is often the best method for homeowners to tackle active weeds because the liquid “coats the leaf surface directly.” This total coverage allows the plant to absorb the product more efficiently than other methods.
| Pros: | Cons: |
| ✓ Fast-acting ✓ Easy to customize concentration ✓ Good for spot treatments ✓ Works well for large areas with tractor-mounted sprayers | ✗ Can drift in wind and damage desirable plants ✗ Requires spraying equipment ✗ Risk of overapplication ✗ May stain concrete or stone surfaces ✗ Can cause skin and eye irritation |
Application tip: For best results, apply them on calm, dry days when temperatures are between 60–85°F. Be precise; keep the spray away from your flowers and shrubs.
Granular post-emergent herbicides
Granular herbicides are solid particles spread with a broadcast or drop spreader. These products usually settle on the soil and must be “activated” by water—either through a sprinkler or light rain—to break down and release the active ingredients.
While they are easy to spread over large areas, Rice notes that their success depends on precision.
“Granular products rely heavily on proper watering and weather to work as intended,” he explains. If it doesn’t rain or if you over-water, the herbicide may not reach the weed effectively.
| Pros: | Cons: |
| ✓ Less drift than liquids ✓ Easier to apply evenly with a spreader ✓ Longer shelf life ✓ Extended control with some formulas | ✗ Requires watering after application ✗ Slower to act than liquids ✗ Uneven coverage if spreader isn’t calibrated ✗ Risk of runoff into water sources |
Application tip: Water within 24 hours of application, or apply before expected rain.
Selective vs. non-selective post-emergent herbicides
Selective post-emergent herbicides
Selective herbicides target specific weed types—broadleaf weeds, grassy weeds, or sedges—without harming your grass. However, they only work if you match the chemical to the plant. If you use a broadleaf killer on a grassy weed, it won’t do anything.
DiAngelis warns that not correctly identifying the weed you’re trying to kill is an expensive mistake:
“We had a client property where the manager kept buying broadleaf killer for what turned out to be yellow nutsedge—a sedge that laughs at broadleaf herbicides.”
After wasting $200 on the wrong products, the issue was fixed with a single application of a sedge-specific formula. As DiAngelis puts it, “It’s about chemistry matching the plant structure you’re targeting.”
Note: Always check the label to ensure the product is specifically rated for the weeds in your yard to avoid wasting time and money.
Best for: Treating specific weeds in established lawns
Common targets:
- Broadleaf weeds: dandelions, clover, chickweed
- Grassy weeds: crabgrass, foxtail
- Sedges: yellow nutsedge
| Pros: | Cons: |
| ✓ Safe for lawns when applied correctly ✓ Targets specific weed problems ✓ Available for small yards and spot treatments | ✗ Weed-specific, so you may need multiple products ✗ Less effective on very young or very mature weeds ✗ May require repeat applications ✗ More expensive than non-selective options |
Read more: 6 Effective Ways to Get Rid of Crabgrass
Non-selective post-emergent herbicides
Non-selective herbicides kill all plants they contact, including grass, flowers, and shrubs. Because they do not discriminate between a weed and a plant you want to keep, they must be used with extreme caution.
Rice recommends these products for areas where you want to clear away all vegetation.
“Non-selective ones are better for spot treatments in gravel, cracks, or renovation areas, where everything needs to be cleared,” he says.
Best for: Driveways, sidewalk cracks, gravel areas, fence lines, or clearing land before replanting
| Pros: | Cons: |
| ✓ Kills all vegetation without identifying individual weeds ✓ Effective for total vegetation control ✓ Works on multiple weed species at once | ✗ Will kill grass and desirable plants ✗ Reduces vegetation diversity ✗ Can harm soil microbes ✗ Requires careful application to avoid damage |
Read more: How to Get Rid of Torpedograss
Common post-emergent herbicide ingredients
Different active ingredients target different weeds. You must choose the specific ingredient for your weed problem. For example:
- Broadleaf weed killers often combine 2,4-D, MCPP (mecoprop), and dicamba. Triclopyr is also used in broadleaf formulations, particularly for specialized control of clover and woodsorrel.
- Crabgrass killers typically use quinclorac, sethoxydim, or fenoxaprop-ethyl, depending on the growth stage and specific conditions.
- Total vegetation killers use glyphosate or glufosinate.
Use this chart to match the correct chemistry to your specific weed:
| Active Ingredient | Type | Best For | Available Forms |
|---|---|---|---|
| 2,4-D | Selective, systemic | Broadleaf weeds (dandelions, clover, plantain) | Liquid, granular |
| Dicamba | Selective, systemic | Broadleaf weeds (thistle, knotweed, spurge) | Liquid, granular, powder |
| Glyphosate | Non-selective, systemic | All vegetation (total weed and grass control) | Liquid, granular |
| Glufosinate | Non-selective, contact | Nutsedge, ground ivy, foxtail (alternative to glyphosate) | Liquid, granular |
| MSMA (Methanearsonate) | Selective, contact | Crabgrass, nutsedge | Liquid, granular |
| Bentazone | Selective, contact | Yellow nutsedge, annual sedges | Liquid |
| Triclopyr | Selective, systemic | Woody weeds, poison ivy, clover, chickweed | Liquid, granular, powder |
| Fluazifop | Selective, systemic | Grassy weeds only (crabgrass, foxtail, barnyard grass) | Liquid, granular |
How to choose the right post-emergent herbicide
1. Identify your weeds
Before buying any product, you must categorize your weed into one of three groups to pick the right product:
- Broadleaf weeds: Have wide leaves with net-like veins and often produce showy flowers. Dandelions, clover, and chickweed are the most common types.
- Grassy weeds: Look like your lawn grass but behave differently. They have long, narrow leaves with parallel veins. Examples include crabgrass and foxtail.
- Sedges: Triangular, solid stems. Roll the stem between your fingers; you’ll feel three distinct edges or corners—nutsedge is a common lawn sedge.
Can’t identify your weeds? Use a weed identification app or contact a Lawn Love professional for help.
Read more: How to Control Weeds by Type
2. Consider your treatment area
When choosing herbicide, consider soil composition, weed growth habits, and the surrounding ecosystem.
- Lawns: Use selective herbicides only
- Driveways, sidewalks, gravel: Non-selective herbicides work fine
- Gardens and flower beds: Carefully apply selective herbicides or remove weeds manually
3. Match the herbicide to your weed type
Match the herbicide’s action to the weed’s life cycle and your lawn goals for maximum effectiveness:
- Systemic for perennial weeds with deep roots
- Contact for annual weeds that don’t regrow from roots
- Selective for lawn weeds to protect your grass
- Non-selective for total vegetation removal
Read more:
4. Choose your application method
The application method affects precision, speed, and safety. Choose based on your situation:
- Liquid: Best for spot treatments and fast results
- Granular: Better for even coverage and reduced drift; requires watering
Read more:
5. Consider environmental impact
Protect your family, pets, and local ecosystem by choosing herbicides that break down quickly and minimize environmental impact.
Look for:
- Low toxicity formulas
- Quick breakdown in soil
- Minimal runoff risk
- Organic or eco-friendly certifications when available
6. Check compatibility
If using other lawn products (fertilizers, pre-emergent herbicides, insecticides), verify that they can be applied together or how long to wait between applications.
7. Factor in cost vs. effectiveness
Balance your budget with long-term results. Systemic herbicides cost more upfront but may require fewer applications than contact herbicides.
FAQs
Apply when weeds are actively growing, and temperatures are between 60-85°F. Early morning or late afternoon works best to avoid heat stress on plants.
Avoid application of a post-emergent herbicide if rain is expected within 24 hours or on windy days (wind over 5 mph can cause drift).
Concentrated formulas require mixing with water, offering better value for large areas and customizable strength. Ready-to-use products come pre-mixed in spray bottles—convenient for small yards and spot treatments but more expensive per application.
Wait until new grass has been mowed 2-3 times before applying selective post-emergent herbicides. Check product labels for specific waiting periods—most require grass to be established for at least 30-60 days.
Professional weed control services
Choosing the right herbicide, application method, and timing can be tricky. If you’d rather leave it to the pros, Lawn Love’s local weed experts can identify your specific weeds and apply the most effective treatments safely.
Our services also include ongoing maintenance strategies—like proper mowing heights, aeration, and overseeding—to keep weeds from returning. Get a free quote for professional weed control, with most treatments ranging from $50 to $200, depending on your lawn size.
Read more:
- How to Apply Pre-Emergent Herbicides
- How to Get Rid of Chamberbitter
- How to Kill Winter Weeds in Your Lawn
Main Image: Spraying post emergent herbicide on lawn. Image Credit: Shutterstock
Related Posts:
