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How to use salt to kill weeds

How to use salt to kill weeds

John, Passionate gardener, Cambridge

Guide written by:

John, Passionate gardener, Cambridge

92 guides

Salt is commonly used to weed pathways and patios, as well as flowerbeds and vegetable gardens. However, salt can be harmful for soil life meaning it can only be used as an occasional solution alongside less harmful weed killing methods. Read on to find out all about using salt as a weed killer. 

Important features

  • Salt as a weed killer
  • Applying salt to weeds
  • Disadvantages of salt weeding
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There has been a lot of interest in alternative weed killers in recent years with many of us moving away from harmful herbicides like glyphosate. A few common household products can be used to deter weeds and many have the advantage of being entirely natural.

One of these such products is salt. Salt is a raw material found abundantly around the world both in seawater and salt mines.

While salt is an entirely natural substance, it doesn't come without its risks to the environment. In fact, salt can actually have serious consequences for soil fertility.

Used too often, salt will modify the structure of the soil causing it to harden and eventually suffocate plant roots. If excessive amounts of salt are used, it can take years for soil to regain the structure it needs for crop growth and plant life in general, especially if it was originally clay heavy. Many countries with hot and dry climates have issues with excessive soil salinity. This phenomenon is called salinisation and usually occurs when there is too much salt in irrigation water and not enough drainage.

The salt does not break down in the soil but rather seeps down to the groundwater. Furthermore, salt is toxic to soil microfauna and earth worms and can lead to a loss of biodiversity. Salt is not only damaging to soil, it also affects water. Freshwater aquatic life is very sensitive to any changes in the salinity of water.

Often, even the plants you do not treat with salt will end up absorbing some salt through their root systems. Trees are particularly affected as their nutrient-seeking roots can extend very far from the trunk. These roots may work to concentrate salt found in the soil which can eventually kill them. De-icing salt is a common source of salt pollution in cold climates.

Concentrations of salt in the soil make it more difficult for plants to absorb water. Certain plants are tolerant of salty environments. Salicornia and halimiones, for example, will thrive in coastal areas. However, these halophytes are only able to cope with these conditions as they have evolved to grow in saline soils.

Coarse or fine grain kitchen salt will work equally well at killing off weeds. Salt is always readily available and costs pennies compared to products you can buy in the shop. Curing salt is an effective herbicide and de-icing salt can also be used. However, bear in mind that the latter usually also contains magnesium chloride or calcium chloride which make it less effective.

  1. Sprinkle coarse salt onto any plants you want to eliminate. The ideal time to do so is after the morning dew or in drizzly weather.
  2. Dissolve about 200 g of salt in 1 litre of water and spray it onto any plants you hope to kill.
  3. Some gardeners will add a white vinegar solution to the concoction to work as a herbicide.

Quick tip: salt will dissolve more easily in warm water. In fact, you can even use boiling water as this in itself is an effective plant killer.

Salt works to kill weeds in two ways:

  1. It increases the levels of ions in the soil and increases osmotic pressure: as a result, the plant will be unable to absorb water and will dry out.
  2. It adds toxic mineral ions to the soil in the form of sodium which replaces the mineral ions that the plant needs to survive such as calcium, magnesium and potassium.

In conclusion, using salt to kill weeds should be avoided in any areas where you plan to grow crops. There are many other options that will prove less damaging to the environment. However, salt can be used as a last resort to kill off any stubborn weeds in any paved areas, stone patios or gravelled paths.

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Guide written by:

John, Passionate gardener, Cambridge, 92 guides

John, Passionate gardener, Cambridge

When I was young, I was already working in the family garden. Perhaps that is where my interest in plants and gardening came from. So, it was logical for me to study plant biology.   At the request of various publishers I have, over twenty-five years, written many books on the subject of plants and mushrooms (a subject that is close to my heart). They were mostly identification guides at first, but shortly after they were about gardening, thus renewing the first passion of my childhood.   I have also regularly collaborated with several magazines specialising in the field of gardening or more generally in nature. There is no gardener without a garden, I have cultivated mine in a small corner of Cambridge for the last thirty years and this is where I put into practice the methods of cultivation that will I advise you in as well.

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