Ah dear, time to talk about every gardener’s worst nightmare…weeds!
I think we all agree that having the odd weed here and there is par for the course in the garden. However, these pesky plants can spread so rapidly, they easily have the potential to invade entire lawns and flowerbeds.
Forks, trowels and hoes are good to have in the armoury against weeds. But sometimes you need something more. An effective weed killer can help truly eliminate unwanted weeds, keeping your garden looking pristine. Plus, they’re not only useful in the battle against common weeds; certain weed killers can get rid of brambles, nettles and thistles as well.
The following information will help you work out how to find the best weed killer for your garden:
Different Varieties of Weed Killer
There are a range of weed killers on the market and they attack weeds in different ways:
- Selective weed killers are usually safe to use on lawns as they won’t kill off the grass. They will only target and kill specific types of plans (eg. weeds). These are normally clearly sold as lawn treatments, so if it a weed killer doesn’t mention being safe for lawns, don’t use it on grass (unless you don’t mind the grass getting scalded).
- Non-selective weed killers will kill any plant they come in contact with. These need to be applied with care, to make sure they don’t get on any grass or prized plants by accident.
- Systemic or industrial weed killers have the strength to kill even resistant plants like brambles and briars. These products are absorbed into the plant itself, traveling down to the root, killing the plant from the inside out. They generally work slower than other weed killers, but can be more powerful.
- Residual weed killers are applied to the soil and prevent seeds from germinating. Whilst they do stop weeds from growing, they tend to stop any other plants from germinating either. They are long lasting, remaining active in the ground for around 12 months.
- Natural weed killers are made from natural ingredients. While these tend to be less effective than industrial strength weed killers, they are safer to use on your lawn and kinder to wildlife. More details can be found about the ingredients found in commercial natural weed killers in the “Ingredients in Weed Killers” section below.
- Some people also choose to use homemade natural weed killers, using a solution of white vinegar, salt and liquid dish soap.
How Weed Killers Work
Weed killers use herbicides to control, limit and stop plant growth.
The actual chemicals vary depending on the type and brand of weed killer, but they tend to work in a combination of the following ways:
- Stopping Photosynthesis. Plants need light in order to survive and create food, a process known as photosynthesis. Some weed killers work by stopping the plant’s ability to photosynthesise, starving the plant.
- Stopping Protein Production. Protein production is another essential element of plant growth and health. Some weed killers stop plants from being able to produce proteins. Ultimately this causes the plant to die. Glyphosate works this way; however, do your research before using products which contain Glyphosate – is has been shown to have negative effects on health.
- Introducing Different Hormones. The plant’s hormones dictate its growth. Some weed killers contain plant hormones that, when applied to the plant, confuse the plant’s growth system. It eventually becomes deformed and dies.
Ingredients in Weed Killers
Whilst there are a lot of ingredients that can go into weed killers, some are used more commonly than others.
The ingredients dictate what type of weed killer it is, and often a combination of ingredients are used.
Here we will look at the ingredients of weed killers, based on what type of weed killer they’re most commonly used in. There are selective weed killers (only targeting certain plans), non-selective weed killers (not fussy about what plants they kill) and organic weed killers (using ingredients from nature).
Be careful using weed killers around food plants. Many of them are unsafe for use around crops. There are some which are considered to be ok, but you should always do your own research on specific products and read the label carefully.
Ingredients Commonly Found in Selective Weed Killers
These ingredients are used because they specifically target certain types of plants. Therefore, they are often found in selective weed killers as they shouldn’t kill of grass or other vegetation that they’re not intended for.
Generally, a combination of these ingredients is used to make the weed killer more effective.
- Fluroxypyr – specifically targets plants like cleavers and other similarly broad-leafed weeds.
- Dicamba – effective against broadleaf weeds like milkweed, as well as woodier plants like brambles.
- Mecoprop-p – good at controlling knotweed and clover as well as other broadleaf weeds before they have reached maturity.
- Florasalum – effective against dandelions, white clover and daisies before the plants have reached maturity.
- Clopyralid – combats tougher weeds like thistles and clovers
- MCPA – stands for ‘2-methyl-4-chlorophenoxyacetic acid’ and is used to keep broadleaf weeds like thistle at bay.
Ingredients Commonly Found in Non-Selective Weed Killers
These ingredients are used because they will attack any type of plant. They may be used in different concentrations, with other ingredients as well.
- Glyphosate – kills the majority of plants, including perennial grasses, so it’s not one that you want to accidentally get on the lawn or flowerbed. It is effective at killing well-established weeds because it works from inside the weed itself. After being absorbed by the leaves and stalk of the weed, glyphosate spreads to the rest of the plant, including the roots. In recent years, it’s developed a reputation for being dangerous; however the jury is out on a definitive conclusion. Some studies have found it to be carcinogenic, whilst others consider it safe for humans to use as long as the instructions are followed. Glyphosate is also thought to negatively affect wildlife such as bees and aquatic life. It can stay in the soil for a long time as well.
- Flazasulfuron works on weeds when they first start growing, as well as when they are in their ‘adolescent’ stage. It’s absorbed by the roots and then works its way through the rest of the plant.
Ingredients Commonly Found in Organic Weed Killers
Weed killers with organic ingredients can still be strong, and contain harmful ingredients as well. However, organic ingredients are generally considered less damaging for the environment and wildlife.
- Pelargonic acid is the most commonly found active ingredient in organic weed killers. It’s a naturally occurring acid in geraniums. This acid is generally considered effective at controlling the growth of smaller broadleaf weeds (under 15 cm tall).
Organic weed killers are less likely to stay in the soil, and may be suitable for use near food crop plants. Also, you can often plant into the soil at soon as the weeds are gone, instead of having to wait for the chemicals to leave the soil. (again, check the label of the specific weed killer you’re using).
General Weed Prevention
After treating your garden with weed killer, you’ll have a clean slate. But how can you stop the vicious cycle of weeds growing back?
Well, prevention is the best cure and there are several tactics you can use to keep weeds away. You might prefer some methods over others, or consider using a combination:
- Prevent weed seeds from germinating by using a weed killer that stays in the soil. This will stop weeds from growing, but will also stop any other plants from germinating as well.
- Consider mulching. A thick layer of organic mulch can prevent weeds from taking over your garden. This will help the soil retain moisture while also suppressing small weeds.
- Use thick weed-control fabric/weed membrane. A weed-control fabric/weed membrane can prevent weeds from growing. It’s perfect to use under paths or decking. It allows water, nutrients and air to pass through, while stopping weeds growing. These are generally very easy to lay and offer a cost-effective way to prevent garden weeds. If you want more information about weed membranes and how they can help, check out this weed membrane page.
- Don’t leave bare soil. Weeds thrive in open spaces in the soil. Plant vegetables, flowers and shrubs close together to minimise open areas where weeds can pop up.
- Fertilise grass regularly. This can prevent new weeds from growing on the lawn. Fertilising can help grass build a healthy root system which can choke out weeds, whilst improving the condition and look of your lawn at the same time.
When to Apply Weed Killer
It’s important to note that the chemicals in most weed killers are not as effective during warmer temperatures.
This is not necessarily due to any shortcoming of the herbicide itself, but related to how plants absorb moisture. Most plants absorb more moisture in the cool temperatures of the early morning, but stop when temperatures rise in the afternoon.
So, for the best results, apply your weed killer early in the day.
All weed killers have the potential to be washed into other areas through rainwater runoff.
Spraying during windy conditions can also cause the chemicals to spread to areas that you did not intend to treat, killing plants that you wanted to save.
Therefore, you should avoid using weed killer if you know it’s going to rain or if it’s windy.
Other Methods for Removing Weeds
Using a chemical weed killer may not be everyone’s first choice. Sometimes, it becomes the only option, especially if you are up against an overgrown garden of brambles, or persistent weeds that won’t stop coming back.
However, there are some other weed-removal options that you can consider, or that you might want to use alongside chemical weed killers:
- Some weeds can be killed by simply pouring hot water over them. This can be effective on patios and driveways but will scald grass if used on the lawn.
- Use a long-handled weeding tool, or a weeding knife. This makes weeding more a manual process, but there are some effective tools that make the job less backbreaking. You might like to check out this page on weeding tools to find out more.
- Purchase a weed burner to pinpoint certain weeds. These tools are designed to heat weeds and make their cells burst, causing them to die. They’re quite effective, and can stop bigger weeds like dandelions from growing back. If frazzling your weeds to death sounds like something you’d be interested in, you can check out our page on weed burners.
- Regularly hoe any loose soil to combat small weeds. This can be both a preventative and offensive measure; it discourages weeds from taking root as well as disrupting the growth of new weeds.
Getting rid of weeds without chemicals can be hard work, but it can be done.
Keeping informed about the growing habits of different weeds can help, as you can try to dissuade certain species from growing in your garden.
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