Can bleach be used as a weed killer?

Originally used as a bleaching agent to remove colour from fabrics, bleach gained popularity throughout the 19th century as a disinfectant thanks to its ability to kill germs including bacteria, viruses and fungi.

An extremely powerful product, bleach is also toxic and corrosive. It can burn the skin and irritate mucous membranes (in the eyes, for example), particularly in its undiluted form.

Bleach must never be mixed with any other products, especially those containing acids. So just in case you were thinking about using vinegar to boost the properties of bleach, you should know that by doing so you will create a highly toxic cocktail! When bleach and acid are mixed, chlorine gas is released which, even in small amounts, can irritate the eyes and airways.

In fact, bleach is responsible for thousands of household accidents each year.

It's fairly common to come across various online 'recipes' or tips involving bleach – but many are extremely bad ideas in practice. Considering bleach is capable of destroying all kinds of life forms, there's no doubt that it will work as a weed killer. But at what cost to the environment?

Bleach is a dangerous biocide that will readily leach into groundwater. Bleach breaks down fairly quickly but releases salt and chlorine in the process which will combine with other elements to form harmful substances in the soil, water and even in the air.

Of course, there are many other less harmful – or even completely harmless – ways to eliminate weeds.

Manual weeding

Getting rid of weeds by hand is the only feasible option if there's little space between your plants and using the right weeding tools is the only way to ensure your weeds won't come back.

This is what is referred to as selective weeding. It is completely safe for soil and microbial life, and is also easy to do provided the soil is moist enough. You can always use a hand weeder to pull out any weeds with deep roots and a garden hoe will make the job much easier.

Flame weeding

A weed burner is a great way to weed small areas or pathways. Petrol-powered or electric weed burners are designed to apply high concentrations of heat directly to the plant. A weed burner can be used to eliminate weeds on a plot before crops come up or between rows of crops. The downside of this method is that it will heat up the top layer of soil.

Mulching

This natural method works to prevent photosynthesis in weeds by blocking out the light. This will eventually kill off the plant. Weed control fabric can be laid as a permanent solution to deal with weeds in areas with prolific growth such as on slopes or between ornamental plants in a flowerbed. Laying weed control fabric, tarpaulin or even black plastic sheets works really well if you are hoping to eliminate weeds over an entire plot before planting crops or laying a lawn.

Natural weed killer

Natural weed killers may be made using ingredients such as pelargonic acid or acetic acid which is also present in vinegar in low concentrations. These weed killers are known as contact weed killers. This means that they are not selective but rather will kill any plant leaves or stems the product comes into contact with. These products are known as foliar herbicides.

Bleach or sodium hypochlorite can be used in other ways around the garden. That said, it is still only recommended to use this product very occasionally and for targeted uses bearing in mind that even small amounts of bleach will end up in nature.

Disinfecting tools and equipment

You can use bleach to disinfect pots and planters that you want to reuse. Dilute the bleach to a 10% solution in cold water. Leave the tools to soak for 30 minutes before rinsing thoroughly.

Tomato stakes can be rubbed with the same solution before being stored for the winter to prevent fungal diseases in future crops.

Tool blades (secateurs, pruning knives, grafting tools, knives and so on) should be disinfected between plants to prevent disease spread. In this case, bleach can be used undiluted instead of alcohol.

Treating diseases and targeting parasites

Some gardeners harness the biocidal properties of bleach to deal with fungal diseases. A highly diluted bleach solution (2 tablespoons of bleach for 2 litres of water) can be sprayed onto the leaves of affected plants.

Safety precautions

No matter what you are using bleach for be sure to follow all safety precautions including wearing protective gloves, masks and safety goggles. It is essential to protect your skin, airways and eyes against any contact with the product.