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Can You Spray Roundup after Rain

Weed control in a garden can seem daunting. Thankfully, herbicides like Roundup can make it easier. However, gardeners might be tempted to spray the weeds as soon as the rain ceases when the weather is not nice and sunny. Is this a good or bad idea?

What is Roundup

As a new herbicide or weed killer in the 1970s, Roundup was good news for most gardeners. Along with other pesticides that use the active ingredient glyphosate, it quickly became widespread in use. Monsanto, a US-based agricultural chemical company, initially made the herbicide commercially available.

Originally formulated for large-scale farming needs, Roundup weed grass killer soon found in the home, backyard garden versions. The brand has since become a go-to household weed killer at the consumer level. Some variants are now available, like Roundup Max Control and Roundup Extended Control, offering avid gardeners many choices. (Read How Long Does it Take For Grass to Grow)


How Roundup Works

The active ingredient glyphosate is a non-selective systemic herbicide. How it works is it can exterminate practically any kind of vegetation via absorption through the foliage. A plant’s vascular system soaks in the weed killer to all parts of a plant.

This includes the roots, which thus kills it quickly. Weeds are usually dead in a day. Glyphosate will not absorb into the roots through the soil, and it has to come into contact with the leaves to penetrate the weeds.

Can You Spray Roundup after Rain

Roundup is most effective when used on dry foliage. If the herbicide comes into contact with wet foliage, it may not be as well absorbed. Rather than be absorbed into the leaves, it could simply wash away with water.

Most of the weed killer ends up running off with water onto the soil, where it is not effective. While some herbicides can stick to the foliage for absorption, they may be insufficient to kill weeds.

Home-Recommended Solutions

A roundup solution that is ready to use (no preparation needed) is the best kind for hobby gardeners. It contains a diluted solution that is a mere 2 percent glyphosate. This potency is good at getting rid of weeds and unwanted shrubs.

Using Roundup on wet leaves dilutes the glyphosate and water, further lessening the already mild potency of the solution meant to be soaked by foliage.

Effective Wet-Day Usage – How Long Does Roundup Need Before Rain

Whenever rain seems likely, it is advisable to spray before the downpour. Be aware that Roundup requires just 30 minutes to absorb into the foliage. After 30 minutes, rain cannot wash it off, so Roundup before rain is the optimal time to use it.

On the contrary, after rain, it could require a few hours for leaves to totally dry, particularly if the conditions are humid. Furthermore, when spraying before the rain, do so only if winds are not preceding the downpour. Spraying weeds while windy may result in herbicide drift as the droplets are disturbed by the blustery condition.

Once again, the magic time frame is to apply Roundup 30 minutes before rain, ideally even earlier, but not later.


Effect on Nearby Plants

If rain begins to pour sooner than 30 minutes after spraying Roundup, the rain will likely wash off the chemical. There is no need to fret and worry about the herbicide washed off harming surrounding plants in such a case. The solution’s active ingredient, glyphosate, will penetrate around 6 inches into the soil.

Nevertheless, it sticks to the soil and does not travel through it to penetrate other plants in the vicinity.

Roundup and Its Efficacy with Wet Leaves

A few plant-care products like fertilizers need plants to be a bit damp for the products to adhere to the leaves. Roundup is surely not one of those products. It does its work best if the leaves are thoroughly dry and it has a fast absorption rate.

Safety Precautions When Using Any Herbicide

Before using any weed killer, fertilizer, pesticide, or plant care product, always use garden shoes, long slacks, a long sleeve top, gardening gloves, a mask, and safety goggles. This is to prevent any contact with the skin and the eyes. Also, make sure not to inhale the fine mist or powder.

Prepare any formulations with the utmost care, following directions. Since it is a non-selective weed killer, Roundup will exterminate many varieties of plants , including your prized ones. Be sure to spray only the weeds and shrubs.

It is recommended that this is done early in the day or evening when temperatures are above 60 degrees Fahrenheit with little wind disturbance.  Always wash your clothes after applying Roundup or any plant care product. Be sure to wash well using hot water and soap to remove any chemical residue.

It is also good to keep pets and kids away from a sprayed place until the area is arid.


Spraying Roundup after Rain

Even though not ideal, there are times when spraying after a downpour might be the only option. As such, after rain, wait until the foliage is dry before spraying the leaves with Roundup. This could be a wait of hours, so be patient to be able to control weed proliferation.

Efficacy of Roundup with Dew

As most gardeners know, dew settling on leaves creates a thin film of water droplets or moisture. Misting moist weeds with Roundup early in the day when dew still lays on the foliage could compromise its efficacy. (Learn Why Won’t My Peppers Turn Red)

Spraying the herbicide when heavy dew is present can surely cause both the product and moisture to slip off the leaves and to the ground before the leaves have a chance to absorb the solution. Since early in the day is the best and most convenient time for most gardeners, wait for a morning after a night of thick cloud cover.

Such atmospheric conditions aid in keeping heat close to the ground. This prevents dew from forming early in the morning.

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