Weeding via the use of chemical products is not the ideal solution for many gardeners who would prefer to avoid using them. However, there are times when this approach is justified, as long as the correct doses are used !
When you do not have the time to weed by hand or by mechanical methods but you want to keep the soil clear of weeds there remains only two solutions: use of a mulch or chemicals. Only the latter will keep the soil bare. There are times when weeding is obligatory (regardless of the method employed!), such as in areas that are infested by ambrosia grass which is very allergic. It must be destroyed before the 15th August otherwise you risk a fine. Chemical weed-killers are also useful when dealing with particularly tenacious weeds such as Japanese knotweed. As it is usually found in places that are difficult to get to and any other method would involve quite radical solutions to destroy it.
Which weed-killers ?
The choice of weed-killers for the amateur gardener is quite limited and legislation is only getting tougher. You can only now get products that are relatively safe. The most common weed-killer available contains glyphosate. This substance, which has been talked about at length, has the advantage of acting in a systematic way, meaning throughout the entire plant. The plants that come in contact with the weed-killer die completely. It is not selective and will kill cultivated plants as well as weeds. You must be very careful when applying it, use a spray with a guard so that it does not stray onto neighbouring plants, alternatively apply with a paint brush onto a few of the leaves of the plant to be destroyed.
The other chemical weed-killer is acetic acid, which is concentrated vinegar. It is applied using a spray onto driveways, paths and other areas that need to be kept clear. When concentrated it is corrosive but it does not remain in the soil. Vinegar is effective against young plants that are starting off. It only kills the part of the plant that it comes into contact with and does not prevent new growth from the roots or underground stems.
Pelargonic acid has recently arrived on the scene it is a natural weed-killer just like the vinegar. It is powerful against the new growth of plants on paths and paving as well as algae.
Apply weed-killers using suitable equipment : wear clothing that protects your body and protective gloves. Spray only in good weather with no wind. Set aside a spray that is used only for weed-killer solution: if not you risk damaging other plants if the spray has not been thoroughly rinsed out or contains a small amount of residual weed-killer.
Be careful with nearby watercourses !
The law is very clear do not use weed-killers next to watercourses! It is forbidden to spray weed-killer within 5 metres of a watercourse or a body of water such as a lake or pond that is shown on a map and a distance of 1 metre for all other watercourses must be respected. Glyphosate breaks down rapidly in the soil into various sub-products that remain in the soil and can find their way into underground water. Great attention must be paid to not use weed-killer near to a watercourse and doses must be adhered to. Vinegar is also very toxic to aquatic life forms.