As cooler weather rolls in, many homeowners focus on raking leaves and preparing their lawns for winter; however, fall is also the best season for weed control. Broadleaf weeds, winter annuals, and even invasive grasses like annual bluegrass thrive during this transition.
Soil temperature, weed type, and timing all play a role in whether herbicide applications succeed or fail. The strategy is different than springtime maintenance.
Fall is (Arguably) the Best Season for Weed Control
Weeds don’t slow down when summer ends. In fact, fall weeds often become more active as cooler temperatures arrive.
Broadleaf weeds such as dandelions, chickweed, and clover send energy to their root system in fall, making them more vulnerable to weed control treatments. This is when post-emergent herbicide applications are most effective because the chemical travels with nutrients deep into the plant.
"By fall if you have weeds then you need to use a product that will kill typically broadleaf weeds and not the grass. Several makers have these on the market," shared Lou Manfredini, Ace Hardware’s Home Expert.
Waiting too long can reduce results. "Once temperatures are consistently below 50 degrees then that will be too late to see any effects and you are better off waiting until the following spring," he adds.
The Balance of Soil Temperature and Timing
Soil temperature matters more than the calendar.
While many think “first frost” signals the end of lawn care, soil temperatures often remain warm enough for weeds to keep growing.
"The weed killer works best when soil temperatures are between 50-75 degrees which usually corresponds to the air temperature," adds Manfredini.
Pre-emergent herbicides help block weed seeds from sprouting, especially problem grasses like poa annua (annual bluegrass) and other winter annual weeds. Meanwhile, post-emergent herbicides target visible growth of broadleaf weeds and creeping weeds such as ground ivy and creeping Charlie.
To time applications effectively, pay attention to both soil temperature and recent weather conditions. A soil thermometer can help you gauge when it’s right.
Common Fall Weeds to Target
Even though summer is over, weeds don’t disappear. In fact, fall brings a new wave of lawn weeds that take advantage of cooler soil and reduced competition.
"[You'll find] the same weeds that came in the spring and summer," shares Manfredini, quickly listing some common competitors including Dandelions and crabgrass. The growth can be fierce, even disrupting determined grasses like Kentucky bluegrass or perennial ryegrass, stealing nutrients and moisture before winter.
Below are some of the most common weeds to watch for in fall:
- Dandelions – Broadleaf perennials that spread quickly through seeds. Yes, you can pull them, but you have to do it right.
- Chickweed – A winter annual broadleaf weed that thrives in cool, damp soil.
- Annual bluegrass (poa annua) – A winter annual grass that germinates in fall and produces seed heads in spring.
- Creeping Charlie (ground ivy) – A tough perennial weed that spreads by stolons and crowds turf grass.
- Crabgrass – Though typically a summer annual, lingering seeds can sprout late if soil stays warm.
Each of these lawn weeds requires a slightly different approach.
Pre-emergent weed control stops annual weeds and annual bluegrass before they sprout, while post-emergent weed killers work on active growth.
For persistent perennial weeds like Canada thistle or creeping Charlie, multiple herbicide treatments may be needed over several treatment cycles.
FAQ
When should I apply a pre-emergent herbicide in fall?
Apply a fall pre-emergent treatment when soil temperatures cool to about 70 degrees but remain above 55. This timing prevents winter weeds from germinating while still catching weed seeds at the right stage.
Can I still use a weed and feed product in fall?
Yes, some granular products combine fertilizer applications with weed killer (we covered fall fertilization in more detail earlier this month). These can strengthen turf grass before winter while reducing fall weeds.
Remember: Check the application rate and timing for your specific grass type, and don't wait until too late in the season. If you wait until it's dormant, you've waited too long.
What’s the difference between pre-emergent and post-emergent herbicides?
Pre-emergent herbicides prevent weed seeds from germinating. Post-emergent weed control products attack weeds already visible.
Both have a place in a fall lawn care program depending on whether you’re targeting winter annuals, perennial weeds, or broadleaf plants.
