Ants can spark a debate with gardeners. Some will say that they’re harmless and that they’ll actually help pollinate your flowers. But other gardeners have had definite problems with these little insects.
Regular tiny garden ants won’t cause damage to your garden unless you also have aphids. The ants won’t do any damage themselves, but they will promote aphid growth. They will "farm" the aphids in order for the honeydew that they produce. The aphids excrete a sweet secretion after they eat the plant sap from your leaves, and the ants love this.
Carpenter ants, on the other hand, will need to be exterminated right away. They will eat anything wooden, such as trellises, benches and even parts of your apartment building! They can cause a lot of damage. Carpenter ants are easily recognizable because they’re much bigger than regular ants.
If you want to get rid of ants, try these methods:
Ant traps. You can purchase ant traps at your local garden shop and leave them out.
Sprays. In a garden setting, especially a kitchen garden with edible plants, it is usually best to stay away from bug sprays.
Food. Sprinkling pepper or cinnamon around the balcony garden will supposedly keep ants away. Dry cornmeal will also work (after the ants eat the cornmeal, it enlarges in their stomach and they die). Some have said that sprinkling Splenda or Equal around will also kill them. There are many other spices that you can spread around that will kill the ants.
The best thing to do when dealing with an ant problem in the balcony container garden is to find the anthill where they’re coming from. The ants may be climbing up from the ground below your balcony garden, and it isn’t always possible to get the anthill. If you do find the mound where they are coming from, you can pour boiling water into the mound. This will even kill the queen, and that colony will leave you alone for good.