What time of year to spray post-emergent? Fairhaven, MA
- May 9
- 10 min read
by Jorge Melo | New England Tree & Landscape Inc.
UMass research shows crabgrass starts germinating in Massachusetts soils when surface temperatures hit 55°F for four or five consecutive days, usually right around the forsythia bloom in late April.
Most homeowners across Fairhaven and New Bedford miss that pre-emergent window, watch the weeds explode in summer, and end up needing post-emergent rescue work instead.
So, what time of year should you spray post-emergent? Here is the short answer: spray post-emergent when the weeds are actively growing, and the lawn is not stressed.
For broadleaf weeds like dandelion, white clover, chickweed, and plantain on South Coast Massachusetts lawns, spring and especially early fall are the strongest windows.
For crabgrass that already escaped, late spring through summer is the post-emergent window while the plants are still young.
Post-emergent timing changes with the weed, so the calendar answer depends on what you are looking at in your lawn.
The short answer: it depends on the weed you are targeting
Post-emergent is not one season on the calendar. It changes with the weed.
If you are dealing with dandelions, clover, chickweed, plantain, or other broadleaf weeds, do it in the spring and fall, with early fall usually being the strongest window in Massachusetts.
If you are dealing with crabgrass that has already come up, do it in the late spring through summer while the plants are young and actively growing.
If you seeded the lawn recently, the rules change again, and you may have to wait before any broadleaf product touches the new turf.
Weed type | Best window | Main caution |
Broadleaf (dandelion, clover, chickweed, plantain) | Early fall (mid-Sept to mid-Oct), then late spring | No spraying above 85°F or on stressed turf |
Crabgrass (already emerged) | Late spring through summer, while plants are young | Mature crabgrass resists post-emergent control |
Winter annuals on new fall turf | Only after at least three mows | Many products injure new seedlings |
What post-emergent weed control actually means
Post-emergent herbicide is a weed killer used after weeds have already come up. Pre-emergent works on seeds before they sprout.
A selective herbicide kills certain weeds without killing the lawn.
The most common active ingredients for broadleaf weeds in cool-season turf are 2,4-D, dicamba, and triclopyr.
For escaped crabgrass, quinclorac is the most common active ingredient in homeowner products.
Spraying the wrong product at the wrong time on a cool-season lawn in North Fairhaven or Acushnet Center can damage the turf without solving the weed problem.
When to spray broadleaf weeds like dandelions, clover, and chickweed
Broadleaf weeds are the dandelions, white clover, chickweed, plantain, and ground ivy that show up in almost every lawn we see across the South Coast.
UMass Extension says annual and perennial broadleaf turf weeds can be managed with postemergence herbicides any time the weeds and the cool-season turf are actively growing, but applications are best done in fall and spring (UMass).
Why is early fall usually the best time
As temperatures drop in September and October, broadleaf weeds shift into winter prep mode.
They pull sugars down from the leaves into the roots for storage. Herbicide applied to the leaves rides that same downward flow straight into the root system, which is what kills a perennial weed for good.
A dandelion you spray in the fall is moving the chemical exactly where you need it to go.
That is why our lawn weed control program in Fairhaven leans heavily on early fall treatments across Sconticut Neck, East Fairhaven, and Mattapoisett Center.
Why spring is still a good window
Spring works because the weeds are young, actively growing, and have thinner leaf surfaces that absorb herbicide more readily.
Late April through early June covers most of the South Coast.
The problem is that perennial weeds in spring are pushing energy upward to produce leaves and flowers, not downward to the roots.
You will knock back what you can see, but the root system often survives, and the weed returns. Spring treatment is worth doing on visible weeds.
Plan on a fall follow-up because spring alone rarely finishes the job.
Why summer is usually not ideal
Two things have to go right for a broadleaf herbicide to work.
The weed has to absorb it, then move it down to the roots.
Summer heat and drought disrupt both.
Stressed weeds develop a thicker waxy coating on the leaf surface that blocks absorption.
Even if some herbicide gets in, a plant that has slowed its metabolism in the heat is not actively translocating anything. What does get absorbed stalls out before reaching the roots.
On top of that, the cool-season turf in most South Coast lawns is already under heat stress, and broadleaf herbicides above 85 degrees can injure the grass itself. Spot treating a healthy, well-watered lawn can still work.
Blanket applications in July and August are a waste of product and a risk to the turf.
When to spray crabgrass after it appears
Crabgrass is a summer annual grassy weed, not a broadleaf, so the timing is different.
UMass says crabgrass begins to germinate when surface soil reaches about 55°F for four or five consecutive days (UMass).
In Fairhaven and New Bedford, that lines up with the forsythia bloom in late April. Once crabgrass is visible, you are past prevention.
Late spring to early summer timing
The post-emergent window for escaped crabgrass is late spring through summer, while plants are young and actively growing.
Quinclorac products work best on small crabgrass with one to three tillers. Once those plants mature in mid to late summer, control gets harder.
If you find crabgrass creeping along the pavement edges of a driveway in Howland Mill or the South End of New Bedford, hit it early.
Coastal lawns near pavement and salt exposure tend to warm faster, so crabgrass shows up there first.
Why post-emergent crabgrass control is a backup plan
UMass says preemergent applications should be completed before forsythia flowers drop, usually by late April or early May (UMass).
Pre-emergent is the real solution.
Post-emergent is the rescue when the pre-emergent window was missed.
We cover the full strategy in our post on how to get rid of crabgrass in your South Coast Massachusetts lawn, and the timing in our guide on when to apply pre-emergent in Massachusetts.
I missed pre-emergent. Now what?
This is the most common situation we see across Fairhaven and New Bedford.
Spring got busy, the forsythia dropped flowers, and the pre-emergent never went down.
Now it is June, and crabgrass is showing along the driveway. Your options shift to:
Spot-treat young crabgrass in late spring and early summer while plants are still small.
Hit broadleaf weeds with a targeted treatment in late spring if the lawn is healthy and temperatures stay below 85°F.
Plan a strong fall broadleaf treatment in mid-September to mid-October.
Mark next spring's pre-emergent on the calendar so you do not repeat the cycle.
When not to spray post-emergent herbicide
Skip the spray entirely when any of the following are true:
Temperatures are above 85°F. UMass Best Management Practices says not to apply herbicides if temperatures are above or forecast to exceed that mark (UMass). Purdue notes warm-weather broadleaf applications above 80°F should be avoided because turf burn is more likely (Purdue).
The lawn is drought-stressed. UMass advises homeowners to avoid broadleaf postemergence applications when cool-season turfgrasses are heat- or drought-stressed (UMass). If the lawn is browning out or crunchy underfoot, wait for steady moisture or push the work to fall.
The lawn is newly seeded. New seedlings cannot handle broadleaf herbicide until the turf has received at least three mowings (UMass).
The weeds are mature or not actively growing. A flowering dandelion in May is a great target. A seeded-out, hardened dandelion in dry late July is not. Mature plants resist treatment.
I seeded my lawn. Can I still spray?
Mostly no, at least not right away.
UMass says winter annual broadleaf weeds in late summer and fall turf seedlings can be controlled with broadleaf herbicides only after the turf has received a minimum of three mowings (UMass).
Many post-emergent products also carry label restrictions for weeks before or after seeding. If you seeded a thin patch through East Fairhaven, a blanket broadleaf spray over that area can stunt or kill the new seedlings.
The cleaner approach is to plan: spray in spring, renovate in late summer, then follow with a fall broadleaf treatment after three mowings.
We lay out the timing playbook in our guide on when to overseed your lawn in Fairhaven, Massachusetts.
When weed spray alone will not fix the lawn
Thin or patchy turf
If your lawn has more weeds than grass, no spray schedule will fix it in the long term. Bare soil grows weeds. Thick turf crowds them out.
A patchy lawn off Mattapoisett Neck or in Acushnet Heights usually needs renovation work, not another round of herbicide.
Weeds that keep coming back every year
Recurring weeds are a sign that the lawn is too thin, compacted, or underfed to compete.
Stronger fertilization, better mowing height, and core aeration and overseeding make a bigger difference than another spray.
Our lawn fertilizing service and lawn mowing program cover the basics.
When overseeding or renovation makes more sense
UMass says late summer renovation from August 15 to September 15 generally yields the best turf-establishment results because minimal weed competition and cooler conditions follow (UMass).
For lawns that are 40% or more weeds, a fall renovation through our lawn renovation service beats another year of spot treatment.
Post-emergent vs pre-emergent: when each one makes sense
Pre-emergent stops weed seeds from germinating. It goes down before forsythia flowers drop in spring to block crabgrass.
Post-emergent kills weeds that are already up and visible.
You need both.
Skipping pre-emergent forces you into post-emergent rescue mode, which is harder, more expensive, and less reliable.
Our breakdown on when to apply pre-emergent in Massachusetts covers the spring side in detail.
Frequently asked questions about post-emergent timing
What time of year should you spray post-emergent?
Spray when the weeds are actively growing, and the lawn is healthy. For broadleaf weeds like dandelion and clover on South Coast, Massachusetts lawns, early fall (mid-September to mid-October) is the strongest window, with late spring as the second-best option. For escaped crabgrass, late spring through summer, while plants are still young. Skip spraying when temperatures climb above 85°F.
Is spring or fall better for post-emergent weed control?
Fall, for most broadleaf weeds. Purdue, UMN, and NDSU all point to fall as the strongest window for perennial broadleaf weeds because the plants pull sugars and herbicides into their roots before winter. For crabgrass that already came up, the answer flips: late spring and summer matter, since the plants need to be actively growing for the herbicide to work.
When should I spray dandelions in my lawn?
Mid-September to mid-October is the strongest window in Massachusetts. Late spring, around or just after the flower flush, is the secondary window. Skip midsummer treatments on stressed cool-season turf. Our lawn weed control service in Fairhaven, MA times dandelion treatments around those windows for the lawns we maintain through Acushnet, Fairhaven, and New Bedford.
When should I spray clover in my lawn?
Mid-October is the strongest window for white clover, paired with stronger annual fertilization through the rest of the season. Spring spot treatment can help if clover is spreading visibly, but fall is where most of the real control happens. Purdue specifically calls out mid-October and warns against warm-weather applications above 80°F.
When should I spray crabgrass after it appears?
Late spring through early summer, while crabgrass is still young with one to three tillers. Once the plants mature, post-emergent control gets unreliable. The better long-term plan is pre-emergent next spring, before forsythia flowers drop. Watch the pavement edges of driveways and walkways in places like Howland Mill and the South End of New Bedford, since crabgrass shows up there first.
Is summer too late for post-emergent weed control?
For broadleaf weeds on cool-season lawns, summer is usually too stressful for blanket spraying across South Coast Massachusetts properties. Spot treatment on healthy, well-watered lawns can still work. For escaped crabgrass, summer is part of the rescue window as long as the plants are still young and the temperature stays below 85°F.
Can I spray post-emergent right after overseeding?
No. Most broadleaf products require new turf to receive at least three mowings before treatment. UMass spells this rule out for fall turf seedlings. If you overseeded thin areas in East Fairhaven this fall, wait through the three-mow window. The simpler plan is to spray in spring, renovate in late summer, then follow up after three mowings.
What is the difference between pre-emergent and post-emergent?
Pre-emergent kills weed seeds as they germinate, before the plant breaks the surface. It is the main tool for stopping crabgrass in spring on Massachusetts lawns. Post-emergent kills weeds that are already up and visible. Most lawn programs need both for the best results. Our pre-emergent timing guide covers the spring side in detail.
If weeds keep coming back, do I need renovation instead of more spraying?
Often, yes. If the lawn is more than 40% weeds, the underlying problem is thin turf, compaction, or low fertility. Spraying alone will not fix those. A late-summer renovation in the August 15 to September 15 window through our lawn renovation service usually solves the problem better than another year of herbicide.
Is spot treating better than blanket spraying?
For most home lawns with scattered weeds, yes. Spot treatment hits the problem without stressing the rest of the lawn or wasting product. Blanket applications make sense when more than 30% to 40% of the lawn is broadleaf weeds, or as part of a fall broadleaf cleanup before overseeding the next year.
Do you offer lawn weed control in New Bedford and Acushnet?
Yes. Our lawn care services cover Fairhaven, New Bedford, Acushnet, Mattapoisett, and the surrounding South Coast. We handle properties in the North End and South End of New Bedford, Acushnet Heights, North Fairhaven, East Fairhaven, Sconticut Neck, and Mattapoisett Center, and we tailor weed control timing to each property's lawn type and conditions.
What makes New England Tree & Landscape different?
In our 35+ years of business, we have built our weed control work around UMass guidance and real conditions on South Coast lawns rather than one-size-fits-all calendar sprays. That means fall broadleaf timing, careful summer spot treatment, and honest renovation recommendations when a lawn is past the point where spraying alone will fix it.
Need help with post-emergent timing on your South Coast lawn?
If you are tired of watching the same dandelions, clover, and crabgrass come back every year in Fairhaven, New Bedford, or Acushnet, we can help.
Call New England Tree & Landscape at 508-763-8000, email request@newenglandtreeandlandscape.com, or visit newenglandtreeandlandscape.com for a free estimate on a weed control program built around your lawn, not a generic schedule.
Sources
University of Massachusetts Amherst. "Section 3: Weed Management." Professional Guide for IPM in Turf for Massachusetts, UMass Extension, https://www.umass.edu/agriculture-food-environment/book/export/html/9735.
University of Massachusetts Amherst. "Best Management Practices: Weed Management." UMass Turf, https://www.umass.edu/agriculture-food-environment/turf/publications-resources/best-management-practices/10-weed-management.
University of Massachusetts Amherst. "Biology and Management of Crabgrass." UMass Center for Agriculture, Food, and the Environment, https://www.umass.edu/agriculture-food-environment/home-lawn-garden/fact-sheets/biology-management-of-crabgrass.
University of Massachusetts Amherst. "Crabgrass Management: Homeowner Options." UMass Center for Agriculture, Food, and the Environment, https://www.umass.edu/agriculture-food-environment/home-lawn-garden/fact-sheets/crabgrass-management-homeowner-options.
University of Massachusetts Amherst. "Lawn Renovation and Overseeding." UMass Center for Agriculture, Food, and the Environment, https://www.umass.edu/agriculture-food-environment/home-lawn-garden/fact-sheets/lawn-renovation-overseeding.
University of Minnesota Extension. "Managing Weeds in Lawns." UMN Extension, https://extension.umn.edu/lawn-care/lawn-weeds.
Purdue University. "Dandelions: Friend or Foe?" Purdue Turf Tips, https://turf.purdue.edu/dandelions-friend-or-foe/.
Purdue University. "White Clover in Golf Courses, Sports Turf, and Lawns." Purdue Turf Tips, https://turf.purdue.edu/white-clover-in-golf-courses-sports-turf-and-lawns/.
North Dakota State University. "Managing Dandelions in Your Lawn With Herbicide." NDSU Extension, https://www.ndsu.edu/agriculture/extension/extension-topics/gardening-and-horticulture/lawn-and-yard/managing-dandelions-your-lawn.
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