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The Best Time to Spray Weed Killer

The Best Time to Spray Weed Killer

The time to spray weed killer is a much-debated subject in the gardening community. Some people say that it should be applied when weeds are actively growing, while others say that it should be applied when the ground is frozen. The following post focuses on all the aspects and questions you may get when picking the best time to spray weed killer.

The Difference Between Pre-Emergence and Post-Emergence Herbicides:

There are two types of weed killers: pre-emergence and post-emergence. Pre-emergence herbicides kill weeds before they germinate, while post-emergence herbicides kill weeds that have already germinated.

Pre-emergent herbicides are usually applied in the spring before the weeds have started to grow. Post-emergent herbicides can be applied either in the spring or fall, depending on the type of weed killer you are using.

1) Pre-Emergence Products

Use these weedkillers on specific lawns (as recommended by manufacturers) to try and disrupt the summer weed’s lifecycle. The primary chemicals are Dithiapyr and Benefin.

They work by inhibiting cell division in the weed, so it can’t grow.

They must be watered in to be effective and will take a few weeks to start working.

Some common brands are Scotts Halts Crabgrass Preventer and Bayer Advanced Season-Long Weed Control.

Pre-Emergence Products

You apply these before weeds can grow, such as in early spring, and then a second spray 8 weeks later [1]. You can then repeat the week killer after 8 weeks if necessary.

There are many pre-emergence herbicides on the market, but they all work in a similar way.

You would apply pre-emergence herbicides before weeds can grow, such as early in the spring, and then approximately eight weeks later, you would apply it again.

Be careful when using pre-emergence herbicides on new lawns – they can inhibit grass growth as well!

Summer weeds should be dealt with by using pre-emergence herbicides, which are designed to interfere with the weed life cycle.

2) Post-Emergence Products

These weedkillers work after the weed has germinated and are usually a contact herbicide.

This means that it kills the weed by damaging its cellular structure.

They come in both liquid and granular forms, with varying degrees of success against different weeds.

Some common brands are Ortho Weed B Gon Max Control for Lawns Granules, Scotts Weed Out Concentrate, and Bonide Kleen-Up Weed & Grass Killer.

Pick these weedkillers as a last resort – they can damage your lawn if used incorrectly! You would apply post-emergence herbicides when the weed is visible, such as in late spring or summer.

Post-Emergence Products

Pre-emergence herbicides should be used in the early spring before the weed has germinated, while post-emergence herbicides should only be used as a last resort and when the weed is visible.

For example, the most popular post-emerged glyphosate is absorbed by the plant tissues, where it kills the plants’ living cells. This weed control works best on weeds that are still small.

Make sure to read the instructions on the bottle carefully!

Take Care About Safety

Weed killers interfere with the development of weeds by blocking protein synthesis or causing root deterioration. Herbicides are not as hazardous to people as pesticides but you need to use them carefully [2].

Be sure to read the instructions on the herbicide bottle carefully, as each herbicide works differently!

Some general tips for using weed killers safely:

  • Wear a long-sleeved shirt along with long trousers and closed-toe shoes when spraying;
  • Avoid getting the herbicide on your skin/eyes;
  • Do not eat, drink, or smoke while you are spraying;
  • Wait until the spray has dried before going back inside your house;
  • Also consider wearing gloves, goggles, a respirator;

Also, consider keeping your pets indoors before reading the label to find out how long you must stay away from the treated area.

Keep teenagers and children at a safe distance from the treated area for at least 24 hours after application, as well as before and after.

Remember to use common sense when applying weed killers — if it’s windy out, don’t spray; if it’s raining, wait until later. And always follow the specific instructions that come with your herbicide!

Take Care About Safety

Spraying Weed Killers by the Seasons:

1) Winter

Use herbicides during the winter season because weed growth is at a minimum. The cold weather will also kill any plants that are not killed by the herbicide. If the chemicals freeze overnight, they may lose their efficacy.

Make sure to apply herbicides in late winter or early spring when the soil is still cold. This will ensure that the herbicide seeps down into the ground and kills the weed’s roots.

If you’re looking for a spot treatment, use a weed killer that is specifically designed for colder weather. These products work best on perennial weeds like dandelions.

Products like Roundup are not as effective during winter because they rely on heat to activate.

Some people choose to spray their lawns with weed killers in late fall so that any new growth killed over the winter will not be visible in the springtime.

2) Spring

Because it’s warm in the spring, you have a better opportunity to apply pre-emergent ahead of time to keep weeds from germinating. Then, 8 weeks later, use post-emergent to destroy the more tenacious weeds while they’re still small.

Weeds will start to grow at the beginning of spring, so it’s important to spray weed killers at this time. You can either use a pre-emergent or post-emergent herbicide.

Pre-emergents should be applied before weeds germinate, while post-emergents are best used on actively growing weeds.

Products like Roundup work well in the spring because they rely on heat to activate.

3) Summer

In the summer, we must ensure that we spray at the end of the season. You will reduce the issue for next spring by treating weeds in the late summer. You may want to apply the product in the early morning or afternoon and wait for it to dry before you mow. The spray might evaporate in direct sunlight.


Summer is the best time to spray weed killers because there is more sunlight and the temperatures are warmer.

Products like Roundup are most effective during summer because they rely on heat to activate.

4) Fall

This is an excellent time to use weed killers because weeds are most vulnerable. Weeds will have a hard time surviving the winter after being sprayed post-emergent. You should apply two applications of herbicides in October, two weeks apart. If they don’t wilt immediately, wait until spring when we’ll see that the majority of them won’t return [3].

You should use weed killers during the fall season because weed growth is at its peak and the temperatures are cooler. This will help the herbicide to work better.

Some people choose to wait until after Columbus Day weekend to spray their lawns with weed killers in order not to kill any flowers that may be blooming.

Weed killers can be applied at any time of year, but it’s important to remember that different products work better at different times. Make sure to read the product label carefully so that you know when is the best time to apply the herbicide.

Spraying by Time of Day

Many weed killers must be used at particular times of the day. One mistake that many people make is to overlook the influence of their local climate on when to spray weeds:

  • Warm climate. When you’re looking to spray your weeds, it’ll be either in the afternoon or early morning. The temperatures won’t reach above the mid-’80s, and nighttime temperatures will be around 60 to low 70’s degrees Fahrenheit;
  • Cold climate. If you live in a hot, humid climate, it’s not the best time to spray if dew or grass and weeds have dried up. The influence of nighttime cold decreases as the temperature falls, so you can only apply weeds when there is no snow or ice around mid-day when the sun is at its strongest;
  • Temperate climate. Your plants are least active in these regions from early evening until the next morning. The optimum hours for obtaining fruits are between late morning and early afternoon when the sun is at its weakest [4];

Spraying by Time of Day

Weather Conditions:

1) Rain

If rain is in the forecast, it’s best to reschedule your weed spraying. The herbicide will not work as well if it gets wet and could potentially wash away.

It is necessary not to spread the product immediately after it has rained. Otherwise, the herbicide will be severely diluted and just disappear being eventually less effective as claimed. You have to wait no less than 24 hours and spread the product on the plants before and/or after the rain.

If you’re using a backpack sprayer, it’s best to wait until the rain has stopped and the ground is dry before spraying. This will help prevent any weed killer from getting on your clothes or shoes.

If the region receives a lot of rain, you may choose weed killers that are rainfast within 2-4 hours after application.

2) Wind

Wind can also impact how well the weed killer works. If it’s too windy, the herbicide could drift onto unintended plants and damage them. Try to spray on a day when the winds are light.

Use a sprayer to apply herbicide so you can minimize spray drift. Usually, this occurs when herbicide blows to other parts of the yard during windy weather and kills unintended plants.

When the wind is strong, there’s no sense in spraying, therefore we must wait for it to die down, which usually takes place in the morning and at night.

3) Temperature

Herbicides work best when the temperature is between 65 and 85 degrees Fahrenheit. If it’s too cold or hot, the herbicide will not be as effective. Try to spray during this temperature window for optimal weed control.


The best time to spray weed killer in most cases is early morning or evening when temperatures are cool. Early morning hours tend to have light winds and low humidity, while evening hours often have lower temperatures and less wind.

Choose a day that meets these weather conditions for the most successful application!

4) Extreme Heat or Cold

Extreme cold or heat can also impact how well the weed killer works. If it’s too hot, the herbicide could volatilize and go away before it has a chance to work. If it’s too cold, the herbicide could freeze and not be effective. Try to spray when the temperature is moderate.

Humidity is also important. Because liquid evaporates before it can absorb in extremely hot conditions, and freezes in extreme cold, humidifiers aren’t effective at those temperatures.


1. Why does the time of year affect weed killers?

The best moment to spray weed killer is in the spring. This is because you may find weeds when they are still in their early growth stage before they have had a chance to fully develop. Spring has the benefit of being both warm and wet, which makes it ideal for weed control [5].

2. What are the best conditions when applying weed killer?

It depends on the weed killer type. Systemic herbicides, for example, are most effective when applied in the early morning, mid-day, and late afternoon in chilly or cold weather. Plant growth slows down at dusk and resumes at dawn the next day.

Herbicides may run off due to heavy early-morning dew, so it’s best to put them out after the dew has vanished [6].

Some of the best conditions to apply almost any weed killer are:

  • When it’s unlikely to rain for at least 6 hours. You don’t want the weed killer to be diluted by the rain. When the plant absorbs this, it will be less effective because of its dilution;
  • On a calm day. A gust of wind may carry the spray away from the intended region. On a more tranquil day, it’s ideal to aim for a certain area;
  • Avoiding high sunshine, frost, or freezing temperatures is recommended. In hot rather than cold weather, weed killers are more effective, but both ends are difficult;

Hot and dry weather encourages plant hardiness along with proper development, which lowers the amount of herbicide that enters and travels through the plant. If you’re using herbicide-based weed killers, the heat will make them less efficient, so target weeds in the spring or fall.

It’s also not a good idea because it makes it difficult to grow plants. Plants utilize their metabolism to break down herbicides. However, plant metabolism slows down in the cold. As a result, the amount of time it takes for the plant to react to the herbicide and be destroyed is prolonged.

It might be difficult to adequately manage your weeds when you have a long list of criteria to consider. A weed killer that doesn’t include herbicides is a good way to avoid these issues. This is because it will be less susceptible to the weather and other circumstances [7].

3. Does the type of weed impact how effective weed killers will be?

Yes, weed killer’s effectiveness varies depending on the sort of weed you wish to eliminate. This is due to its life cycle.

There are numerous distinct sorts of weeds, and you’re undoubtedly aware of that. If you haven’t already, check out our complete guide to invasive weeds here. All these various types of weeds have varied life cycles, however, this influences the optimum season for removing them.

Some weeds develop in the fall and winter, but others do so in the spring and summer. Some weeds are more enduring and will take two years to complete a life cycle before dying. Some will return year after year.

4. Does rain affect herbicides?

Yes, rain affects herbicide effectiveness since it washes away any solution that must be applied to the surfaces. Some herbicides need 6 to 8 hours of dry, rain-free weather for the solution to enter into the root zone, and these parameters should be stated on the label [8].

5. Can I spray weeds before it rains?

You’ll need to give the herbicide ample time to work before any rain falls while spraying weeds. Depending on the brand you select, it’s suggested that you spray 30 minutes to an hour before the rain, if not sooner, depending on the situation [9].

6. Can I spray weed killers when it’s hot and dry?

It is generally advised that you should wait until the weeds have had some rain before spraying them, rather than doing it when they’re dry. When plants are distressed, they thicken their cuticle, which reduces the amount of moisture in the leaves. The uptake of herbicides is reduced when the moisture level decreases during hot dry periods. If you live in a hot environment, this will have an impact on when to spray weeds.

When there’s a sign of rainfall, some gardeners spray moist-stressed weeds believing they’ll lessen weed seed germination. However, waiting for new leaves to appear after the rain is a better strategy, resulting in more effective weed control.

7. Do you have to pull weeds after spraying?

After spraying, you should be able to see changes in a day or two. You’ll have to remove them manually after they die, which is difficult, but not nearly as challenging as pulling a live weed. These pesticides have the disadvantage of leaving some weeds alive [10].

8. How do you stop weeds from growing back?

There are a few various techniques to remove weeds for good [11]:

  • Pulling the nasty weeds manually, by hand;
  • Using a hoe to remove stubborn and deep weeds;
  • Using chemical weed killers;

The optimum time to remove weeds is when the soil is wet and damp. Weeding on the day after it rains is a fantastic idea. Damp soils are easily removed because they are loose. Otherwise, you run the danger of leaving your roots in place if they get caught in the earth. If the ground is solid and no rain is expected within days, consider watering it down with water and allowing it to soak overnight before performing any work.

1) Pulling Weeds by Hand

If you have time, the most effective and least difficult way to get rid of dandelions is to dig them out by hand. Keep in mind that this method will be ineffective unless the entire plant is removed with its roots. You can simply grasp the plant by the stem and pull gently if weeds with shallow roots are present.

If your weeds have deep roots like dandelions, you’ll need to take greater care when removing them. To loosen the soil around the stem, use a tiny hoe to dig in beneath it; then grip the stem firmly and pull. You may need to dig deeper and attempt pulling repeatedly until you successfully remove all of the roots.

2) Pulling Weeds with a Gardening Tool

Hand-pulling weeds can be time-consuming and strenuous. Gardening tools might be used to assist with this activity. A regular garden hoe may be used for shallow-rooted weeds, but a specialized tool called a winged weeder is required for deep-rooted ones.

To remove weeds with the winged weeder, place the bottom tip of the blade right next to the stem and press down vertically to push the blade into the soil, and then tilt the weeder downwards towards the ground to pull out the entire root. This method may be performed multiple times as necessary. These tools are available from any hardware store.

3) Using a Chemical Weeding Product

You may apply chemical weed killers directly on weeds using a pump-action sprayer or a hand sprayer. It’s not environmentally friendly, so use it only if absolutely necessary. Some, like Ortho’s Weed-B-Gon, kill a variety of weeds including dandelions, crabgrass, and clover. This solution is non-damaging to the lawn. Alternatively, you may get the concentrate and mix it with water to Spray where needed.

Another disadvantage of these chemicals is that they may not kill the weeds entirely. The chemical only kills what it comes into contact with, and if it was not sprayed properly, the weed may survive, so be sure to cover all undesirable plants adequately.

You can also prevent weeds from developing by using weed preventer granules, such as Preen, which work for a few months at most. Some bottles include a convenient dispenser that allows you to apply the granules to plants, bushes, and trees.

9. What temperature should I spray weed killer?

It depends on the weed killer type. In many regions, the temperature after an application of herbicides should be between 65F and 85F. However, with other fall operations, this range is not always feasible. Herbicides can be used at temperatures ranging from 40F to 60F, but weeds may be destroyed more gradually [12].

10. When should I do weed control?

The optimum season to use weed killer is spring, followed by fall.

Spring is when you should try to get rid of weeds before they develop since it’s when they’re most vulnerable. Because it’s when weeds are most susceptible in the winter, fall is also effective [13].

Useful Video: How to Spray Weeds | Beginner Weed Spraying Tips


  1. https://yardandgardenguru.com/best-time-to-spray-weed-killer/
  2. https://housegrail.com/best-time-to-spray-weed-killer/
  3. https://housegrail.com/best-time-to-spray-weed-killer/
  4. https://yardandgardenguru.com/how-to-grow-onions-in-pots/
  5. https://www.weedingtech.com/blog/what-is-the-best-time-of-year-to-use-weed-killer
  6. https://www.hunker.com/13406514/the-best-time-of-day-to-apply-weed-killer
  7. https://www.weedingtech.com/blog/what-is-the-best-time-of-year-to-use-weed-killer/
  8. https://www.hillsirrigation.com.au/spraying-weeds-before-after-rain-is-it-still-effective/
  9. https://www.hillsirrigation.com.au/spraying-weeds-before-after-rain-is-it-still-effective
  10. https://dengarden.com/gardening/How-to-Prevent-Weeds
  11. https://dengarden.com/gardening/How-to-Prevent-Weeds
  12. https://cropwatch.unl.edu/2017/low-temperature-and-frost-may-affect-efficacy-burndown-herbicides
  13. https://www.weedingtech.com/blog/what-is-the-best-time-of-year-to-use-weed-killer