I have a split rock driveway and grass is growing in it. How can I kill the grass effectively so it doesn't just come back in 2 weeks?
I also have a driveway like this, and grass grows down the middle, and along the edges. I think it looks fine, but if you can't stand it, there are several methods of elimination.
When cooking spaghetti, steaming vegetables, etc, we have left-over water in the pot when we're done, and we usually bring it to a full, rolling boil, and dump it over patio stones, driveway, etc, where it kills the weeds. As long as it's hot enough to kill the crown of the grass plant, the plant will die. This is time consuming, and won't kill stoloned grasses such as bermuda grass very well.
propane gas torch:
This is also time/energy consuming, but using a weed torch will kill the weeds/grass. Again, if you kill the crown, the root system will die.
Glyphosate (the active ingredient in Roundup) is a systemic herbicide, so it will kill the entire plant if applied to the foliage. It is what I use for these applications, but glyphosate deactivates on contact with soil, so if the rock in your driveway isn't on a soil bed, the chemical may persist for some time, and possibly wash into the groundwater. This is the biggest problem in cities that spray glyphosate to control weeds in the curb/sidewalk. It ends up washing into the storm-water system.
Other chemicals, such as glufosinate, will kill the grass, but not as fast as glyphosate. Also, many other chemicals are designed to kill broadleaved weeds and leave the grass. Thoroughly read the label of any chemical product you use.
None of these are permanent solutions. Many grasses germinate and regrow very quickly from seed (I have mostly Poa Annua in my driveway right now, and usually quite a bit of Digitaria sp. in summer). You will have to retreat every few weeks, unless you apply a pre-emergent herbicide, like isoxaben or trifluralin (the main ingredients in the product I use for lawns)