a 5litre jar of Roundup herbicide

How Long Does It Take for Roundup to Work? background and application

Understanding the effectiveness and application of common weed killers, such as Roundup, is crucial for every horticulturist and farmer. This article explores the details of Roundup, its origins, and how it works on various weeds. Let’s delve into the history of this essential garden tool.

History and Origins of Roundup

Roundup, produced by Monsanto, now a part of Bayer, was first introduced in the 1970s. It was developed as a broad-spectrum herbicide, a game-changer in both the horticulture and agriculture sectors. Its ability to control a variety of weeds made it popular amongst gardeners and farmers alike.

Understanding Roundup

Roundup is a systemic herbicide, meaning it travels throughout the plant, from the foliage to the root system. The active ingredient in Roundup is glyphosate, a compound that inhibits an essential plant enzyme, leading to the plant’s eventual death.

How Long It Takes Roundup To Work

The time it takes for Roundup to work is dependent on various factors, including the type and size of the weed, as well as the specific Roundup product being used. However, on average, Roundup begins to show visible results within 2 to 4 days for most annual weeds. These are plants that grow from seed and complete their life cycle within one year. For more robust or perennial weeds, which live for more than two years, the action of Roundup may take up to 7 to 14 days to become noticeable.

It’s important to note that Roundup works best when plants are actively growing. This is because glyphosate needs to be transported within the plant, and this happens most effectively when the plant is growing vigorously. Therefore, the time of year and the growing conditions can also affect how long it takes for Roundup to work.

Overall, while Roundup starts working immediately after application, patience is needed to see the full results. The weeds may appear to be doing well for several days after the application, but within a week or two, signs of decline should be clearly visible. Remember, the key to successful weed control with Roundup is correct application and patience.

Roundup and Temperature

Temperature plays a significant role in the effectiveness of Roundup. Optimum temperatures for Roundup application are between 60°F and 85°F. If temperatures are too low, plant growth slows down, leading to slower absorption and action of the herbicide. Conversely, extremely high temperatures might cause the herbicide to evaporate before the plant can adequately absorb it.

Rainfastness of Roundup

Rainfastness refers to the amount of time needed for a herbicide to dry and be absorbed by the plant before rainfall can wash it off. Roundup becomes rainfast about 2 hours after application. However, for optimal results, it’s recommended to apply Roundup on a dry day with no rain forecast for at least 24 hours.

Application Rate of Roundup

The application rate of Roundup varies depending on the specific product and the type of weed you’re dealing with. Always check the product label for specific instructions. Generally, a solution of 1% Roundup (1.3 ounces per gallon of water) should suffice for most residential weed control.

Knapsack sprayer rate: 150ml – 500ml per 10 litres of water covers 1000m2

Boom sprayer application rate in agriculture: is from 3 to 6 litres per Hectare in 100 litres of water.

Weeds That Roundup Can Eliminate

Roundup is effective against a variety of weeds including, but not limited to, dandelions, poison ivy, clover, crabgrass, and more. Its broad-spectrum activity makes it a go-to choice for many when dealing with pesky garden invaders.

Roundup On Grass

Just like with other types of plants, Roundup’s impact on grass depends on several variables, including the type of grass, the product’s concentration, the environmental conditions, and the grass’s growth stage. It is also essential to remember that Roundup is a non-selective herbicide, meaning it will kill most plants it comes into contact with, including grass.

On average, you can expect to see results within 2 to 4 days for annual grasses that are in the active growth stage. This is because these types of grasses tend to have a faster growth rate, allowing the herbicide to be transported more rapidly throughout the plant.

Signs of Roundup’s effectiveness may include yellowing, browning, and wilting of the grass. Perennial grasses, however, may take a bit longer to show signs of Roundup’s action due to their more extensive root systems and slower growth rates. In such cases, visible effects might not be apparent until 1 to 2 weeks after the application.

For optimal results, apply Roundup to the grass when it is actively growing and not under any stress, such as drought. The herbicide should be applied on a dry day, and it’s best to avoid rain or irrigation for at least 24 hours after application to ensure the product is adequately absorbed by the grass.

Usage of Roundup in Horticulture and Agriculture

In horticulture and agriculture, Roundup is used to control a wide variety of weeds, which, if left unchecked, compete with crops for nutrients and sunlight. Understanding how Roundup works and using it effectively can greatly enhance your gardening or farming practices.

Take a look at the many different ways you can buy Roundup on Amazon


Despite its widespread use, it is essential to use Roundup responsibly, taking into account its non-selective nature and potential environmental implications. With the right knowledge, Roundup can be a powerful tool in your gardening or farming arsenal, helping create healthier, more bountiful green spaces and crop yields.