Weed killer is ineffective when daytime temperatures go below 40℉ (4℃). This typically makes winter a bad time to spray for weeds. However, you can use weed killer sprays in fall, early winter, or in a region with mild winters. As temperatures dip toward freezing, herbicide applications become ineffective. A weed killer spray will not be absorbed by the plant in weather colder than 40℉ (4℃).
When Should You Spray Winter Weeds?
It’s best to spray winter annual weeds such as annual bluegrass (poa annua), shepherd’s purse, and chickweed as soon as they sprout in fall. By attacking these weeds before they become well established, you can quickly clear your entire lawn of pests. Spraying weeds early also ensures the active ingredients in your weed killer will be effective. Herbicide sprays are only good at killing weeds if daytime temperatures are above 40℉ (4℃).
- To wipe out winter annual weeds, spray them when they sprout in fall.
- If your region typically has freezing winters, make sure to spray weeds before temperatures go below 40℉ (4℃).
- In regions with mild winters, wait until grass goes dormant, then spray the easily spotted green weeds in your yard.
If you live in a region where it’s common for winter temperatures to be above 40℉ (4℃), then you can spray weeds throughout the winter. In regions such as the American South and West Coast it can be beneficial to wait until your grass goes dormant, then spray the green, growing weeds with a weed killer of your choice.
What is the Best Winter Weed Killer?
If you’re looking for easy ways to kill winter weeds, Tenacity herbicide is one of our favorite options. Tenacity is a lawn-safe herbicide that will wipe out broadleaf weeds and many grassy weeds. Additionally, it’s been shown to be effective against annual bluegrass in several university studies. If you are spraying winter weeds while your grass is still green, Tenacity is a great choice for most yards. However, it’s not safe for use on actively growing Bermuda grass.
- Tenacity herbicide is an excellent winter weed killer that is safe on most turf grasses.
- Make sure that any herbicide you use is safe for use on your grass if your lawn is green and growing.
- If your lawn is dormant, you can safely use to Roundup to spray weeds without harming grass.
If your lawn grass is dormant and temperatures are above 40℉ (4℃) then you can spray any green weeds and pest grasses with Roundup. Although Roundup is a non-selective herbicide that is harmful to all plants and grasses, it won’t harm dormant grass. So, you can safely attack green patches of winter annual weeds among dormant grass just by using Roundup.
Can You Spray Weed Killer on Grass in Winter?
Many varieties of weed killer are great for both grassy and broadleaf weed control in winter but won’t harm your lawn. Tenacity kills broadleaf weeds and pest grasses but is safe for almost all lawns. The main exception is Bermuda grass, which can be harmed by Tenacity. If you have a Bermuda lawn, consider using a Quinclorac-based herbicide that kills everything but Bermuda.
- If you are spraying weed killer in winter, it’s best to choose a product that is safe for your lawn grass.
- Tenacity is safe for almost all lawn grasses except for Bermuda.
- Use a product with Quinclorac to safely kill weeds without harming actively growing Bermuda grass.
- Chemical weed killers are not harmful to dormant grass.
- If weeds are dormant due to cold temperatures, weed killer will not be effective.
If temperatures are below 40℉ (4℃), neither grass nor weeds will be harmed by any weed spray. This is because systemic herbicides are absorbed by plants during photosynthesis. As temperatures drop, plants cease respiration and enter hibernation. When this happens, herbicide won’t have any effect. This applies to weeds as well as grass. If the target weed has entered dormancy due to cold weather, your weed killer won’t do any good.
Can You Spray Brush Killer in the Winter?
As long as the brush you are trying to kill is still green and the daytime air temperature is above 40℉ (4℃), you can effectively use a brush killer. Powerful brush killers, like Crossbow, are extremely effective at controlling poison ivy, horsetail weeds, and other brush. As a bonus, they won’t harm your grass. However, make certain you spray at the ideal temperature. Brush killer sprayed in cold conditions won’t be effective
Can You Spread Weed and Feed in the Winter?
The ideal time to spread weed and feed is fall, before winter sets in. Even this winter weed and feed is designed to be spread on your lawn in the fall. The herbicides in weed and feed are best at weed control when temperatures are above 40℉ (4℃). If you apply weed and feed in winter, the herbicide won’t be effective.
- Weed and feed is best spread in fall.
- The weed-killing compounds in weed and feed will not be effective in cold winter weather.
- The fertilizer in weed and feed will be wasted if it is spread on a dormant lawn. The fertilizer will wash out of the soil before the grass starts growing again in spring.
Because weed and feed contains fertilizer, it is best spread in fall when the grass is still actively growing. If temperatures have dropped enough that grass growth has halted, most of the fertilizer in the product will wash out of the soil while the grass lies dormant, wasting your weed and feed.
- Scotts Turf Builder WinterGuard Fall Weed & Feed3 weed killer and lawn fertilizer controls listed weeds and feeds grass in the fall for a better lawn next spring
- Fall weed and feed kills over 50 listed lawn weeds, including clover, dandelion, plantain, morningglory, chicory, evening primrose, and purslane
- Apply weed control plus grass fertilizer to a wet lawn when weeds are actively growing and temperatures are consistently between 60°F and 90°F
Can You Use Weed Killer in Winter?
If you want to wipe out winter annual weeds and pest grasses, remember these rules for application:
- Weed killers applied in temperatures below 40℉ (4℃) are ineffective.
- If your grass is green and growing when you apply weed killer, use a product that is safe for your grass type.
- If your lawn is brown and dormant, you can use any weed killer you wish without fear of harming your grass.
- Apply “weed and feed” products in fall—they are not effective in winter.
By following these tips for spraying weed killers, you can control all types of weeds. However, taking action is key. Because weed killer is seldom effective in the dead of winter, begin your weed control measures in the fall to create a weed-free zone.