« Can I use salt to kill weed? »
« Sure, it’s the perfect organic weed killer! It’s all over the internet. »
It’s not costly, and « sounds » natural – yeah, salt is natural, right? So it shouldn’t really harm the environment.
Now, really? We had heard of using vinegar in the garden, now salt – what the dickens, we’re talking gardening, not vinaigrette! When every website over the internet basically says the same thing on the subject, we at Groww got a tad suspicious, so we started a little research. Now we have the answer to your question :
Should you use salt to kill weed?
- Short answer is « no – don’t use salt to kill weed, it’s toxic ».
- Long answer is below, if you’re curious.
What is salt?
Chemically speaking, salt is Sodium Chloride, a condiment or a food-preservative, the salt you use in the kitchen, pour in water when you make pasta, or sprinkle on lettuces and tomatoes – once it’s in your plate though, not in the vegetable garden.
Some plants that like salt!
True ! Salt-tolerant plants are called halophytes : think about plants native to seasides, deserts, marshes or salt lakes. There are « true », or obligatory halophytes, that survive only with high salinity levels – this is the case of Salicornes for example – and « optional », which will tolerate the same concentrations but can develop normally without.
An image of the Faunistic Reserve of Margherita di Savoia, by emilius da atlantide : some salicorne, and not much else …
For other plants, salt is a poison
For all other plants, salt is a true poison, for two reasons : osmotic influences, and specific ion toxicities.
Since the cells in plant roots generally have a higher concentration of solutes – the organic compounds that the cells carry – than the water in the soil, water flows through the semi-permeable cell walls and into the root cells, and that is how the plant takes up water. However, as the salt concentration soil rises, this difference is reduced, and water does not flow as freely as before into the cells. The plant takes up less water and less nutriments. It may compensate by synthesizing organic compounds such as sugars and organic acids, or accumulate salts to balance the concentration between the inside and the outside. However, this costs energy, with the result being a plant growing and producing at less than the optimum.
Another way salt can affect the growth of plants is by specific ion toxicities. Ions of soil minerals are absorbed by the plant roots and accumulate in the plant over time, becoming toxic overtime, even at low concentrations. Symptoms of ion toxicity can vary by crop tolerance and stage of growth, but often will result in “leaf burning” at the edges, especially on the older leaves.
On top of that, salt has a strong harmful influence on soil organism. And if you’re a Growwer – a user of our app! And if you’re not, you should just check it out! – you know you don’t want that, because you know that a living soil – a soil with healthy, productive organisms – is essential to your plants.
As a result, salt as a weed killer is effective. But it’s toxic . Why?
Salt in your soil never decomposes
Once you have poured salt on your soil, it just remains there. The principle of a living soil requires that everything be consumed, digested, transformed. In short, everything decomposes at some point, and this process is what makes compound nutriments available for the plants. Salt, however, does not decompose. No one in your garden consumes it – except maybe you, on fries.
Pollution is a matter of dosage
It is often believed that « natural » solutions as opposed to « chemical solutions » should be favored. This is rather a misunderstanding of the problem: more than a question of components, pollution is often a matter of dosage . The argument of the « natural » product that would be « nontoxic » does not hold water – so to speak! For example, arsenic is a violent poison, and yet, each of us carries some in his own body, in minute doses! Nitrogen, contained in our urine and so beneficial to our vegetable gardens in the dose of a few diluted watering cans – for this, see our article (in french) on benefits of human urine in the kitchen garden ! – can become an major pollution when concentrations get stronger !
So well, two things one: either you put little salt, and it will not kill a lot of weed, or you put a lot, and you degrade your soil.
Our advice : pull ’em !
Top image credits : Leonid Mamchenkov .