While ants can actually help your yard by aerating the soil and breaking down organic matter, they can also be pests that limit the enjoyment of your time outside in your yard. When ants become bothersome, it's time to look into ant pest control methods. Most ants, including argentine ants and fire ants, can be dealt with in a variety of ways. Carpenter ants, on the other hand, can do damage to your home and should be dealt with by a professional.
One of the most effective methods of natural ant control includes limiting the plants that attract aphids and other honeydew-producing insects. This is the most obvious food source for common ants, so making sure none of your plants specifically attract them will be a powerful first step to preventing an ant infestation.
Sticky barriers can also provide natural ant control when placed on trees and tall plants to prevent the pests from climbing up. Another simple way of controlling ants without pesticides is pouring boiling hot water into the entrance of their nests. Ants can survive underwater, so this is unlikely to kill the entire nest (as the water will cool as it travels toward the queen) but it will certainly take care of the scout ants that are usually traveling around your lawn.
Finally, you can try leaving a low-wattage light on outside overnight near the area with the most ant activity. The change in light can disrupt the ants' foraging patterns.
Boric acid and diatomaceous earth are both low-toxicity chemical compounds that can be used for ant control. Boric acid can be especially effective when paired with the boiling water method - the boiling water will kill ants near the surface and even as the water cools, it will bring the boric acid deep into the nest, killing many more of the ants. You can also make a homemade chemical mixture that scout ants will bring back to their nest, thinking it's food: dissolve 1 teaspoon of powdered boric acid and 10 teaspoons of sugar into 2 cups of water. This mixture can be sprinkled along the ant nests for effective ant control.
Diazinon has also proven effective at killing ants but is only legal for agricultural uses. Other commercial products, such as Amdro, can also be effective, although overuse will cause the ants to develop resistances to these products and make them less effective.