I came across this little oddity the other day: someone was seriously suggesting using salt as a weedkiller in the garden.
After screaming "Are you crazy??!!??" at the screen, I decided to do a little research to find out why anyone would suggest such a daft thing, and it transpires that it's part of the whole eco-warrior "we don't use chemicals" and "Monsanto [makers of Glyphosate] are the Devil" dippy hippy thing.
As you can tell, I'm not a fan of that type of thinking: it's fine when you only have yourself to think of, but if you are growing food to feed the masses (who all want perfect produce, cheap), or if you are paid to produce a beautiful garden within strict time limits (in most cases, I'm only there for half a day a week), then sometimes chemicals - judiciously used - are the only answer.
So why do I shriek in horror at the suggestion of using salt as a weedkiller? Does it not work? Oh, it works all right: it works superly. It will kill any plant or gastropod within range: if you put salt on a slug or on the stem or leaf of a plant, the salt will allow all the water inside the body of the slug or plant to move outside, in a rather drastic manner. This is why slugs and snails "foam" if you put salt on them: the salt draws out the water on the skin where it touches it, and the water inside the creature rushes outwards to fill the gap, gets drawn outside, so more water rushes out... so the creature dies, howwibly. *maniacal laughter in the background. Yes, I know they are all god's creatures, and that I am supposed to be kind and nice to everything, but news flash, a) I am not actually all that nice, and b) sometimes in life we have to make choices, and I would rather have undamaged greenery than have a huge population of gastropods. So there.*
This process is called Osmosis, and you can look it up for yourself if you are interested: in layman's terms, the salt "pulls" the water out of the slug or plant.
The bad news is that salt stays in the soil for ages - not quite forever, but nearly. Do you remember your bible lessons? The bad guys used to "sow the land of their enemies with salt". This means they would scatter salt on the farming land to kill all the crops, and to prevent any new crops being grown there for many years. The "enemies" would die of starvation, or would have to flee the area. It's not an allegory, it was how they actually did it.
So unless you want a garden in which the only things to grow are salt-hardy Oleandar, Rosemary and Butcher's Broom, you do not want to add salt to your soil.
This also goes for killing those slugs and snails, by the way - don't ever sprinkle salt on the ground, or on the critturs: pick them up (if you are squemish, wear latex gloves, or use tongs) and pop them into a jar or pot with some salt in the bottom. Every so often you can empty the shells out into the bin. Do not put them on the compost heap!
There's another reason for not sprinkling salt on the garden to kill slugs and snails: the eco warriors (or "eco worriers" as I think of them) say that it's very efficient, and unlike the blue slug pellets, does not leave any residual poison in the creatures, so they can be eaten by birds or vermin without ill effect. Not true! Just as too much salt in our diet is bad for us, highly salted gastropods are very, very bad for birds, and although I can't find any firm information on this one, I can't imagine that they'd be very good for moist-bodied frogs.
Although I would say that from time to time I empty out my salt pot onto the rough grass in front of my house, and within a night or two, the whole lot have invariably gone, shells and all: so presumably there is something with four legs that likes crunchy, lightly salted, snails.
As an even further aside, when doing the three-yearly re-blacking of the bottom of a narrowboat, I asked what we should do with the masses and masses of barnacles that we scraped off before we could get to the paint. "Oh, just leave them there, on the ground," said the marina's manager: "they'll be gone by morning." And sure enough, they were, shells and all.
Anyway, back to the salt issue: even if you really, really don't want to use "chemicals", what do you think table salt is, scotch mist? It's mostly sodium chloride, but if it comes from brine (ie "natural" sea salt, obtained by evaporating salty water such as sea water or salt lake water) then it will also contain greater or lesser amounts of magnesium chloride, magnesium sulfate, calcium sulfate, potassium chloride, magnesium bromide, and calcium carbonate.
If you choose to go for "table salt" then you should be aware that it has several additives: potassium iodide for one, to give us protection against thyroid disease: plus magnesium carbonate, calcium silicate, calcium phosphate, magnesium silicate, and calcium carbonate.These are added to prevent clumping, and to prevent it from absorbing water.
So it's not exactly "chemical-free", is it? And it's terribly bad for the soil, so just don't use it on the garden: either use the minimum amount of commercial weedkiller - which has been carefully tested, and calibrated to be effective - or just get out there with a daisy grubber and weed by hand or by hoe!