Generally speaking, it can take between 2 and 4 weeks for weed killer to begin to work, but there’s a lot of variance in that number.
The speed with which your weed killer works depends on many different factors.
To determine how quickly your weed killer will work, you’ll need to ask yourself a few questions.
This article presents 6 questions and answers for your consideration when determining how quickly your weed killer will work.
Weed Killer Q&A
1. What Kind Of Weed Killer Am I Using?
Commercial weed killers are specially formulated to damage or destroy weeds significantly.
Some are also explicitly formulated that they only affect certain weeds.
This is why you must clearly identify the weeds you want to eliminate and then read weed killer packaging labels carefully to ensure you choose a product that will work in your circumstances.
If you choose the right weed killer, it will work quickly.
But if you choose the wrong one, it will not work at all and may damage your lawn or desired plants.
2. What Kind Of Weeds Am I Battling?
If you are trying to eliminate broadleaf weeds distributed throughout your lawn, you should look for a selective weed killer.
This type of herbicide harms only specific plants while leaving grasses alone, such as:
- Dandelions
- Clover
- Thistle
- Chicory
Even so, check to ensure that the product you choose is safe for the type of grass you have.
If you have an area that you want to clear of all vegetation- both weeds and grass- you can go with a non-selective weed killer, such as Roundup (glyphosate), which kills everything in its path.
This product is also helpful if very carefully applied to targeted plants.
You can also use a non-selective weed killer to combat winter weeds on some lawns during the dormant season.
For example, when grasses such as Bermuda, Zoysia, and St. Augustine are dormant, they are not harmed by non-selective herbicides.
3. How Old Are The Offending Weeds?
If you act preemptively and apply a pre-emergent herbicide before your weeds have a chance to sprout, you could effectively say that you’ll have immediate results because you may never see the weeds you are battling.
Pre-emergent herbicides are typically applied late in the fall to discourage winter weeds and late winter to discourage spring weeds.
If you are combating established standing weeds, the battle may take quite a bit longer, depending upon the type of weed and the product you choose.
Again, this is why it’s crucial that you accurately identify your weeds, choose a product intended to eradicate them, and then follow packaging instructions exceptionally carefully.
4. What Time Of Year Is It?
In the wintertime, you will be mainly dealing with annual weeds.
Even though they tend to germinate and begin growing in the wintertime, they will continue to grow and thrive well into the spring.
Therefore, it’s best to take care of the weeds early in the winter.
If you let them live, mature, and go to seed, you’ll have a new crop starting when the cool autumn weather returns. [source]
Application of a pre-emergent herbicide late in the autumn and early in the spring should keep annual weeds at bay.
Biennial and perennial weeds typically spread by traveling roots, as well as by seed.
These plants live for 2 or more years and include such demanding customers as:
- Japanese Knotweed
- Wild Carrot
- Ground Ivy
- Dandelions
- Poison Ivy
- Bindweed
- Ragweed
- Plantain
- Burdock
- Thistle
If you live in an area with cold winters, these may mostly die back in the wintertime, but the roots will continue to lie in wait until the warm weather comes.
In the autumn, it’s best to deal with perennial weeds using a systemic herbicide, such as Roundup.
Your goal is to have the product move through the plants’ nutrient system completely before winter comes.
With practical application in the fall, you are sure to see a reduced return of these weeds in the springtime.
Even so, it would be best if you watched for sprouts in the spring and spot treat them with glyphosate as they appear. [source]
5. How’s The Weather?
If you apply the suitable herbicide on a clear, still day, you may see your weeds begin to wilt within a few hours.
However, this does not mean the job is done.
It may still take as long as a month to eradicate the weeds, roots, and all thoroughly.
If you apply herbicide on a day when rain is predicted, you run the risk of having your product washed away before it can do its job.
Likewise, if you use it when the wind blows, you will have trouble controlling it.
This can result in overspray damage to surrounding plants and ineffective application to weeds.
6. How Will My Chosen Weed Killer Work?
There are three main ways weed-killing chemicals work.
They are:
- On contact: If you have actively growing, green, annual weeds, you will apply this sort of herbicide directly to the leaves early in the morning on a clear day.
The chemical will soak into the leaves and kill the plants’ foliage.
Generally speaking, this product should produce complete results within a couple of weeks.
- Absorption: Focused systemic herbicides move throughout the plant’s nutrient transport system and kill all parts of the plant.
This is a good choice for perennials (weeds that come back year after year).
Also, if you have a lot of unwanted clover in your lawn, a systemic herbicide can be helpful.
- Root uptake: A residual weed killer is carried to the weed through the soil.
The roots take it up.
You wouldn’t want to use this type of weed killer in your lawn or garden because it will ruin the soil for both wanted and unwanted plants.
Residual weed killer is an excellent product to use in areas where you never plan to grow anything, such as:
- Gravel driveways
- Paths
- Between pavers
- Cracks in existing patios and other concrete surfaces.
Careful Planning Produces The Quickest Results
It’s easy to see that the effectiveness and the amount of time it takes for weed killers to kill weeds depends on many different factors.
That’s why the purchase and use of weed killers should never be an impulse buy.
Instead, no matter how angry you are at your weeds, take the time to work through these questions so that you can make an informed purchase that will target and kill the weeds you have.