Wondering how long weedkiller will take to kill your weeds? This guide has everything you need to know.
Weed control can be a nightmare for gardeners. No matter how much care and attention you give your outdoor space, it’s inevitable that some weeds will occasionally appear. These unwanted plants can look unsightly and spoil an otherwise attractive display of desired plants. However, they also absorb valuable nutrients from the ground and take up root space, leaving your carefully tended greenery and flora competing with them to survive.
Understandably, most gardeners choose to remove these pesky weeds, and weed killer is one of the most effective ways to do so.
When to Use Weed Killers
The best time to use a weed killer, and ensure the complete death of the weed, is during its growing phase. Generally speaking, this is usually spring and summer. Ideally, weeds should be sprayed before they go to flower. Doing so will prevent annual weeds from reseeding and returning the following year.
While it’s usually best to water plants in the morning or evening, the opposite applies to contact herbicides. Research has shown the best time of day to spray weed killers is around noon, when the sun is at its highest.
Early morning dew can dilute weed killer, making it less effective. Sunlight helps herbicides penetrate the plant, so it is preferable to spray when the weeds can still soak up around 6 hours of sunshine before it gets dark.
How Long Does Weed Killer Take to Work?
Glyphosate is the most commonly used herbicide in the UK and can take weeks to kill weeds completely. Signs of the weed’s ill health may become noticeable in the leaves after only a few hours. However, it takes much longer for the chemicals to reach and destroy the roots.
It’s important to leave enough time to let the weed killer work its magic and kill the whole plant, right down to the roots. If any part of the weed’s root survives, it will likely return at some point.
Even if the weed looks dead on the surface, it’s best to leave around 4 weeks between spraying and pulling the dead weed out. Remember that not all weeds are equal – those with shallow roots will die faster than deep-rooted weeds.
The length of time a weed killer takes to work also depends on its strength. Strong solutions will work more rapidly than less concentrated ones. If it has rained since treatment, the weed killer will take longer to work. Likewise, if the herbicide was applied to the top of the plant, it will need time to reach the roots.
How Does Glyphosate Work to Control Weeds Around Plants in Your Garden or Lawn?
You might wonder how weed killers know the difference between unwanted weeds and desirable plants – why don’t they kill everything in the garden? The truth is that glyphosate herbicides are non-selective weed killers that will destroy all plant growth they come in contact with, whether it’s an ugly-looking clump of groundsel or your most treasured rose bush.
What is Glyphosate?
Glyphosate is the active ingredient in many brands of contact weed killers, including the popular Roundup and Gallup brands. It is a systemic, non-selective herbicide that is strong enough to kill most garden weeds. Glyphosate’s ability to destroy tough perennial weeds resulted in its becoming the most widely used weed control product around the globe.
It gets sprayed on the plant’s leaves, trunk, or shoots, where it enters and spreads to kill the whole plant. Like most herbicides, glyphosate works best when applied to actively growing weeds.
Glyphosate-based weed killers work by stopping plants from synthesizing EPSP – a specific enzyme that renders plants unable to produce the proteins they need for healthy growth. Most plants use this enzyme, so glyphosate kills all plants treated, not just specific weeds.
Targeted Weed Control Using Glyphosate
For this reason, it’s essential to carefully target only weeds. Don’t use so much weed killer that you get lots of runoff, as this can affect healthy garden plants and lawns. Likewise, ensure that you spray on a still day so that weed killer doesn’t get blown onto your prized garden plants.
Once you’ve finished spraying, it is a good idea to lightly water plants to rinse off any stray weed killer and prevent it from being absorbed by the plant’s leaves. Alternatively, you can prune any leaves that have come into contact with the weed killer to prevent them from spreading through the plant.
How Do You Know If Weed Killer Has Worked?
After a couple of days, you’ll start noticing the leaves wilting. A few days later, they’ll begin to turn yellow and then brown, around 7–10 days after application. These are the first signs that the weed killer spray is doing its job.
Reasons a Weed Control Product May Not Have Worked
If the weeds show no signs of deteriorating after around a week, it’s possible the weed killer hasn’t worked. It might be that the weed killer was diluted too much during mixing, so another application with more careful measurements will do the trick.
Drought can prevent absorbed herbicides from being thoroughly distributed around the whole plant. If you plan to kill weeds in the garden during a particularly hot and dry spell of weather, you might want to water them a couple of days beforehand to ensure the solution can be easily absorbed.
Alternatively, it could be that the weed killer itself has been in storage for too long. Outdoor sheds and garages can become very hot and cold during extreme weather temperatures. That can have a detrimental effect on herbicides, rendering the active ingredients useless.
Do Weeds Disappear After Spraying?
When the weed is destroyed, you will be left with its remains. Once you’re sure weed growth has stopped and the weed is absolutely dead, it’s time to remove its remains from the garden.
Hand trowels and forks are best for this job, as they let you get up close and see exactly how much root is left in the soil. Smaller tools are also less likely to disturb other plants.
Use the hand tool to carefully dig up the weed, ensuring you get as much of the root system as possible. If any small pieces of root are left behind, the weed can resprout the following year, so it’s best to take your time. Wear thick, protective gardening gloves and reach right down to the base of the plant before steadily pulling it out. Be careful not to shake off any seeds or seed pods, which can scatter and spread.
You may wish to reapply weed killer 6-8 weeks after the first application to target stubborn mature plants and weed seeds that have germinated.
Loss of Efficiency of Herbicides in Cold and Wet Conditions
A contact weed killer can be weakened by cold or wet weather. Low temperatures slow the rate of growth in weeds. While this might sound like a good thing, it means less herbicide gets absorbed. Avoid spraying weeds when the overnight temperature is likely to reach less than 10ºC. Hold out until later in the season when the weather is a bit warmer.
As for wet weather, water will dilute a weed-killing solution, making it less effective. Recent rainfall will affect how much of the herbicide the plant absorbs, limiting its strength. Check the weather forecast and postpone treatment if it is due to rain in the next couple of days. Moisture will soak the soil and prevent weeds from being fully killed.
Bear in mind that even if the leaves are dry, the soil underneath may still be storing water that makes the roots wet. That’s not to say you need the ground to be thoroughly dried out before applying weed killer, just that it shouldn’t be soaking wet.
Is Weed Killer Harmful to Humans and Pets?
Depending on how you use herbicides, they can be harmful to you and your furry friends. However, when the detailed instructions are closely followed, they don’t pose much risk. Herbicides are much less toxic than pesticides since we have more in common with insects than plants. Weed killers are designed to kill unwanted plants, not people or animals.
When using weed killer, it is sensible to take some precautions to ensure your own safety and that of children and pets.
- Wear gloves, closed-toe shoes, and protective clothing while you apply weed killer.
- Protect your eyes with glasses or safety goggles.
- Carefully read the label and ensure the right amount of weed killer is used.
- Keep children and pets out of treated areas during application and until the weed killer has completely dried.
- Store weed killers securely out of reach in their original containers.
Tips for Using Weed Killers Effectively
- Wait for a spell of mild, still, dry weather for maximum success.
- Check the spray pattern on a concrete driveway or path before spraying plants. Doing this ensures you have the best setting for targeting the weeds you want rid of while minimizing spray on desirable plants.
- If using a watering can, ensure it is a separate one that doesn’t get used to water healthy plants and flowers.
- Be careful not to use too much weed killer to prevent runoff from reaching other plants.
- Leave the waning weed in the ground long enough to die down to the roots before pulling or digging it up.
Weed killers can prove to be quite beneficial for getting rid of unwanted weeds in your garden. It is important that the proper instructions are followed closely when handling weed killers and that the necessary safety precautions are taken so as not to put oneself or other living beings at risk. Weed killers should always be stored securely in their original containers out of reach of children and pets, and the right amount should be used to prevent runoff from reaching other plants. With the right knowledge and practice, weed killers can take care of any unwelcome guests in your garden quickly and efficiently.
So if you’re looking for a reliable way to get rid of troublesome weeds, reach for a bottle of weed killer – just make sure to use it wisely!