What is an effective all natural weed and grass killer?

I was asked this week if i could recommend an effective all natural weed and grass killer. Hope these tips will help

Salt

Salt. Pour Morton table salt between cracks in sidewalks where weeds and grass come up. Pour enough so that it is mounded up an inch or so above the sidewalk. You will be amazed!

Vinegar-the wonderful weed killer...
Vinegar. Or salt, but you can control your application better if you use vinegar (unless you want to go through the trouble of mixing salt with water in a high concentration).

Vinegar is great for many things and when it comes to weeds, it really works, even on Ironweed, a tough cookie. If you need to apply it to a weed or plant that's in the middle of other plants that you don't wish to get a dose, then cut the top off of the weed or plant and dip it in the vinegar. This might take more than onego, so just pour or spray it over the area that needs treatment, and a couple of days later your weeds are dying or already dead.

A Weed Killer formulation I've used for interlocked brickwork is to mix 1 gallon white vinegar, 1 cup table salt, and 1 tablespoon dishwashing liquid. I use 5% household vinegar with great success (my interlock has lots of very young, unestablished weeds). I'm told a 15%-20% strength is better, but I can't seem to find it at a reasonable cost.

Other Ways
To my way of thinking, salt [sodium chloride] and vinegar [dilute acetic acid] are both chemicals! For a truly non-chemical method of spot killing any unwanted weeds or grasses is boiling water, or steam from one of those hand-held generators sold for cleaning. Using this technique, I have encountered only two problems.

First, if the amount and/or area of unwanted vegetation is large, it requires a lot of boiling and hauling of water. And second, if unwanted vegetation is in very close proximity to desirable plants, then great care is necessary to prevent contact of the boiling water or steam with the foliage or root system of those desirable plants which you do not want to harm.

Another method for killing relatively large areas, such as for preparing for flower beds or garden plots, is to scalp mow the grass or weeds, then water well, and cover with a sheet of plastic. Stretch it as smoothly and tightly in contact with the mowed vegetation as possible, and weight it down well, especially around the edges to keep the water vapor contained.

The sun will generate heat, which will be concentrated in the vegetation and soil; and water vapor, which will develop over a relatively short time, will kill the vegetation. I think this method is called solarization.

Another natural method is, after scalp mowing, to simply bury the area which you want to clear of weeds with a 6-12 inch layer of any mulching material. This will kill everything, except the millions of seeds which exist in almost every cubic foot of ordinary soil.

IN ADDITION
i would not advise using the boiling water method however. It can wipe out all the bacteria in the soil as well and make it sterile for at least a year - so be warned