I have a home in the country. I have a 300' gravel driveway. Would spreading rock salt keep the weeds from growing?

vinegar is a good way to get rid of weeds

i have a property in france with a long stone drive ..i use PISTOL  ..works very well

The guy who said it will work but will be more expensive than vegetation killer is right. It will be. Don't think in terms of roundup in gallon jugs. You need a large amount of vegetation killer applied with a tank. You have the tractor. Go to your nearest Tractor supply store or whatever you have near you. They will hook you up with what you need. 

Very bad idea, especially if you have any bodies of water nearby. The salt will be washed away from where you applied it to other areas and kill all the vegetation there also.   There are products designed to kill weeds that more or less stay put after application and are effective for extended periods of time.

Salting the gravel will keep it from growing stuff in it the drawback however is when it rains the salt is going to wash out into the grass around it and kill your grass. The same thing with bare ground weed control you can get stuff that will keep the weeds from growing but when the rain comes and it washes out and gets into the grass it's going to kill the grass and the plants around it.

For a while, but then the salt will be washed away by rain and poison the ground around the drive, too.

Yes, but it would be far more expensive than vegetation killer.