Once you've decided that you're fed up with pulling invading grass up out of your gravel, it's time to finish the stuff off once and for all. Commercial weed killers are effective, but they're loaded with horrible things that the average person can't even pronounce. However, there are simple home remedies that work just as well for killing grass and other weeds without harming you, your pets or the environment. The bonus is that you won't spend a fortune to do this because everything you'll need is probably in your kitchen cabinets.
Boil a quart of water in a saucepan. Take the pan outside immediately. Slowly and carefully pour the boiling water directly onto the undesired grass poking up through your gravel. This kills the grass plant or any other weed by cooking it on contact, so you only need to wet the offending plant completely. Wait two or three days and repeat if necessary.
Pour a small amount of vinegar directly out of the bottle onto the grass. Saturate a sponge with it and squeeze the liquid onto the plants for small areas, if necessary. This substance is also a contact killer, so simply coating all surfaces of the plant will destroy it. Vinegar works by eliminating the plant's capacity to make its own food. Household vinegars contain a five-percent acidic dilution, which is sufficient for this job. Wait a week and repeat if necessary.
Dissolve a 1-lb. box of salt in a gallon of hot water. Slowly stir in 1 cup of liquid dish detergent. Salt has been used for biological warfare to kill the food crops grown by one's enemies since ancient times. Soap has herbicidal qualities. Beyond that, it makes the salt solution "sticky" so that it adheres well to the grass you want to kill. Pour enough of the salt solution directly onto the offending grass to coat all surfaces of the plant.
Put white vinegar or the salt solution in a re-purposed plastic spray bottle. Spot treat wherever pouring isn't appropriate. Repeat in a week if necessary.