Ant hills in your garden are not a problem in themselves, but you'll want to get rid of them regardless. It's what the ants do that causes problems. Ants herd aphids and other garden pests, so controlling ants is one step toward controlling the pests that do the real damage. If you have ant hills in your lawn or garden, there are some simple things you can do to eradicate them and keep them from coming back. When most people think of ant hills, they probably think of those giant spires crawling with ants in some parts of the world. In the US, most ant hills are just small dusty-looking mounds, sometimes with a concave center that has a hole in the middle. These can grow to be several inches high and up to 24 inches in diameter, if left undisturbed. They are more likely to appear during a wet spring.
Rake the ant hill smooth and keep your grass mowed to help discourage the insects. If you don't mind chemical solutions and want to be done with the ants quickly, try sprinkling the hill with a spot treatment of diazinon powder or saturating the hill with a diazinon solution. Read the label carefully for directions on mixing the solution. If you use dust or granules, water it in well after application. Keep children and pets away until the area is dry.
For organic solutions, there are several things you can do. Perhaps the easiest is slowly pouring boiling water down the ant hill. This will kill some ants and repeat applications will give the remaining ants the message that they had better move on. You can chop up some hot peppers in your food processor and add to the boiling water for an additional deterrent. Another option is to flood the ant hill daily with your hose until the ants give up and go elsewhere.
Scoop up a shovel full of ants from one hill and place them in another hill. Take a shovel full of ants from the second hill back to the first hill. Ants are territorial so war will ensue, resulting in the death of many of the ants. Any survivors will get the message and look for safer digs.
Sprinkle diatomaceous earth around the ant hills. The ants coming in and out of the hill will be shredded by this treatment. Since they are the ants responsible for feeding the other ants in the colony, the others will soon die of starvation. A mix of sugar and baking powder may work as well.
In the morning, you can put a can over the ant hill. As the day warms up, the ants will bring the eggs to the surface. Slide a piece of cardboard under the can, and turn the can over. The eggs that are now in the can make a great treat for birds, especially if you keep a flock of chickens.