How can gartner snakes be control in the home landscape?
First, understand garter snakes are not going to do anything to the lawn, will not do anything to your children, and will not hurt you. They cannot bite to hurt, they carry no germs or viruses that will be transmittable to people.
Now, if you still do not want them in the yard, keeping the yard well groomed, making sure there is no place they can hide, and getting a good cat is probably the best way to get rid of them.
We do find lava rock landscaping can sometimes reduce gartner snakes. Snakes will not lie on lava rock because of it's sharp edges, like they will on wood chip mulch or river rock. It needs to be really fresh lava rock, and keep in mind tht lava rock is not good for landscape plants.
There are no repellents that work, UNL Extension Educators have tested all the repellents on the market. Nothing works more than a day or two at the most and most don't work that long.
Habitat modification is the key, so 1) keep everything well mowed, 2) make sure there is no bunches of leaf litter in corners of the yard, and 3) make sure there is no rock piles in the yars. All of these things will help tremendously.