Q: There are ants nesting in one of my garden beds. I looked them up online, and I think they are field ants. Will they damage the plants? The nest is right next to some tomatoes. Is it safe to use ant-killer in a vegetable garden?
A: I asked University of Minnesota Extension entomologist Jeffrey Hahn about ants in the vegetable garden. He says ants are not likely to damage your plants, though they may disturb some roots with their tunneling. Usually, he says, homeowners can let field ant nests be. They are beneficial insects that prey on some of the pests that eat your garden plants.
The other bit of good news is that field ants won’t come into your house and infest your kitchen.
But then there’s the bad news.
Field ants bite, so it may be hard to work around a nest that close to your tomatoes. Field ant nests can persist for years. And if you decide you do want to kill them off, it may be hard to do.
There is some inaccurate advice here and there on the internet about how to kill off an ant nest. It won’t work to pour water on it, even if the water is boiling. It’s dangerous and an environmental hazard to pour gasoline on an ant nest, and it won’t work. Borax won’t work. Herbal remedies such as mint, cinnamon, and cloves won’t work.
The only way to permanently remove a field ant nest is to kill the queen, and that can be hard to do, because she could be 2 or 3 feet underground. Wisconsin Extension recommends poking a hole with a rod or dowel, and then pouring insecticide into the channel you’ve created.
If you decide to go that route, you’ll need to carefully choose an insecticide that is labeled for use near edibles since your ants decided to nest next to your tomatoes.
There’s more information on controlling indoor and outdoor ants here: https://extension.umn.edu/insects-infest-homes/ants#controlling-ants-outdoors-41811.
Written by U of M Extension Master Gardeners in St. Louis County.