Best Time To Apply Roundup

So, I got ready with my full pants, long sleeves, plastic gloves, and safety glasses to battle the countless weeds in my yard. With my sprayer filled with Roundup, I stepped outside just to wonder if it is the best time to apply Roundup on those weeds.


Best Time To Apply Roundup

So, have you ever wondered about what is the best time, like me? Because the ideal temperature as suggested by the manufacturer to apply Roundup falls between 53 degrees and 77 degrees Fahrenheit.

People who do not know much about Roundup, keep reading. Roundup comes from the Monsanto company, which contains glyphosate. Glyphosate refers to a broad-spectrum herbicide that is used for killing all plants that come in contact with it.

Several manufacturers make herbicides utilizing glyphosate with other inert ingredients and herbicides. You can get glyphosate-based herbicides at any garden, home improvement, and farm supply outlets. When using Roundup, you always should follow the usage instructions of the manufacturer.

Roundup is a weed killer that is usually applied to the leaves of unwanted plants like weeds. For ensuring success, you should spray the leaves of weeds until they are fully wet but do not let them drip. You should spray when weeds are growing actively in the summer and spring.

So, the cells of plants pull up glyphosate into the center of plants and kill them down to their roots. As Roundup is a non-selective herbicide, you should avoid spraying it on windy days and overspray might kill your favorite garden plants. Plus, do not spray when it shows rain in the weather forecast. If it begins to rain within six hours, reapply Roundup for killing the weeds.

When is it too hot to spray Roundup?


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Temperature affects the translocation, absorption, and metabolic degradation of the herbicide that you apply to the plants. If you apply herbicides under the wrong conditions, it can fail drastically. However, the reason might not be the herbicide resistance. So, when is it too hot to spray Roundup? Efficacy is great at 20 degrees Celsius than 30 degrees Celsius.

Spraying Roundup is more effective at lower temperatures than under hot weather conditions. When you apply herbicide on cold days, weeds might appear vulnerable to the field rate of Roundup but when you apply the same rate in summer, there might be various survivors.

So, when glyphosate is rapidly taken up, it tends to restrict its own translocation, which could mean that symptoms might appear more in warm temperatures, killing plants is way less reliable.

Best Temperature to Spray Roundup

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Roundup works best while you are applying it to the plants that are growing actively. Usually, this happens in the fall as plants store energy and in the springtime of the year when plants break dormancy. However, Roundup is effective throughout the season against plants. Also, it is pretty easier to look for the right application conditions throughout the summer as compared to fall or spring.

Gardeners can apply herbicides like Roundup when the air temperature remains between 60 degrees and 85 degrees. Fall and spring seasons are too cool for effective herbicide application. You should avoid windy weather conditions and also when you are expecting rain while applying the herbicide.

These conditions do not affect the herbicide’s effectiveness but restrict the unintended transfer of its chemicals to your desired plants that surround the unwanted one. As glyphosate kills all the plants, chemicals washed off the plant’s leaves by rain or blown in the wind can transfer to other garden plants.

Check out this video to learn more about the best temperature to spray Roundup.

Warm Climates

The best times to apply Roundup are late afternoon and early morning in warm climates in summer, like USDA hardiness zone 9 or higher. You should not apply Roundup early afternoon or around midday in summer. This is because midday heat slows down the growth of the plants and chemicals dry out quickly on the leaves. This reduces the herbicide amount that weeds can absorb.

In warm climates in winter, weeds continue growing. At that time, the midday is the best time to apply when the temperature reaches the highest.

Cold or Cool Climates

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Roundup works best when you apply it in the afternoon, midday, or late morning in cold or cool climates. At dusk, the growth of plants slows down and buckles up when the sun rises. Early morning dew could cause Roundup to run off. Thus, it is best to apply it once dew has completely gone.

Points To Remember Regarding The Best Time To Apply Roundup

It is important to examine the weather forecast before you apply Roundup in your garden. So, bear some important points in mind before you spray Roundup.

  • Select a dry, calm day
  • Best to apply when the foliage is growing and green, usually in the summer and spring
  • Do not spray when it is windy as drift might harm your desired plants
  • Do not spray when it is raining outside and if it rains within six hours, you have to reapply the herbicide
  • Do not spray Roundup in extreme cold and hot conditions
  • Do not spray Roundup in extreme cold and hot conditions

When is Roundup safe for pets and children to walk on?

According to the label, Roundup is safe for pets and children as soon as it's dry and has dried completely. But according to the National Pesticide Information Center, pets who come in contact with wet glyphosate products may drool, have upset stomachs, lose their appetites, and become sleepy.

You should wait at least 4 hours before re-entering a treated area. Also, stay away from pets while you're applying your product. It's best practice to stay out until you know that all plants have dried up - which can take anywhere from 30 minutes to 3 hours, depending on conditions.

How long does it take for Roundup to work?

Roundup will dry in 30 minutes to 3 hours. Usually, results are visible within 12-24 hours of application. You will see the weeds yellowed and wilted. And within a week, you'll notice them turning dark brown and then dying. But depending on weather conditions may take longer.

It's always important to read the product label before using any weed killer so that you can properly determine how much of the product to use and when is the best time of day, as well as other potential side effects.

How long does Roundup take to work before rain?

According to the label, they recommend using it on dry, warm days. If it's about to rain, don't worry - all of the products should dry in 30 minutes to 3 hours - some even faster.

How long will this kill the grassroots?

It will take 1-2 weeks for the entire plant to die. Once again, it depends on weather conditions.


Now, you know what the best time to apply Roundup is, Roundup works best within specific temperature ranges. Roundup for weeds control various lawn weeds but it usually does not harm grass.

When the temperature is too low, it may not be that effective and if the temperature is too high, it could damage turf grass. During hot or cold times of the year, you have to wait until the daytime temperature reaches within the right range before applying Roundup in your garden or yard.

If you still have any queries, post it in the comment section below.

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