Most systemic weedkillers have an impact on the plant in hours. That doesn’t mean the plant will die in hours, it simply means the product is working its way through the plant to the roots to begin the process of killing the weed. 

In this respect, it is better to use a systemic herbicide than pull weeds out by hand. Herbicides get right to the root of the weed, removing the risk of leaving some root material behind that can allow a weed to regrow – common with hand-weeding.

Different weeds will need to be treated with different weedkillers. Some weeds, like Marestail, are much tougher and more difficult to kill than other weeds, and other weeds may take more than one application to eliminate.

Contact weedkillers can show results in hours. They work well on annual weeds with less established or extensive root systems. Spot On Pro is a non-selective weedkiller that has acetic acid as its active ingredient. It works well on grasses, broadleaved weeds, and mosses - on various surfaces. 

Preemergent weedkillers

If you want to prevent weeds from taking a hold in the first place, you will want to consider a pre-emergent weedkiller. These specialist products are designed to work on lawns and grassed areas and prevent weeds from developing into mature plants.

Some pre-emergent weedkillers like Proshield are very fast acting; getting to work right away due to their combination of powerful active ingredients.

Prevent weeds from emerging before they get hold

Weed seeds will take hold quickly if the ground conditions are right, so weeds that produce thousands of wind-blown seeds like dandelion should be controlled with preemergent weedkillers to prevent this issue.

Factors that can speed the process

For weedkillers to work at their best (and therefore more quickly), they should be applied at the right time of year, and also at the right time of day. 

Refer to the individual product label, but broadly speaking, post emergent weedkillers work best if applied when the weed is actively growing – usually spring and autumn.

Avoiding temperature extremes can also help improve the effectiveness of weedkillers as will avoiding applying them when rain is due - to prevent wash-off.

Weedkillers that contain glyphosate work best in the morning – allowing it to take effect during the day. Apply on a warm sunny day when the plant is actively growing.

Keeping pets and people off treated areas until the weedkiller has completely dried will help improve effectiveness. Again, refer to the individual product data to check this time period.

Cover the whole weed plant when spraying

Technique can play a part as well. If you are spraying, make sure to cover the whole leaf or plant surface carefully without over-dosing. Applying too much weedkiller can have a detrimental effect due to run-off - reducing its impact. 

Prevention methods

Ideally, we’d be able to prevent weeds from taking a hold in the first place and therefore eliminate the need for weedkillers completely. While this isn’t always practical, there are several steps you can take to help avoid weeds appearing in your garden.

Selecting long-lasting residual weedkillers can help prevent weeds from resprouting, making these products cost-effective. Products like Chikara can control most annual and perennial weeds for up to five months.

Mulching around growing plants or using weed suppression fabric will help stop weeds from growing. Anything that limits light and water getting to the ground will keep beds free of weeds.

Be gentle with your digging and hoeing around growing plants as this can move dormant weed seeds to the surface giving them the right conditions to start growing.

Talk to the experts

There are many different weedkillers to choose from and it can be tricky to understand which weedkiller product is right for your specific weed problem. 

If you want to know more about the differences between selective, non-selective, systemic and contact weedkillers, get in touch with our technical team today for free specialist advice. 

Our experts will be able to provide guidance tailored to your specific situation and give you a more accurate estimate on the length of time you can expect for your chosen product to work.