Among the methods you often hear about how to destroy ant nests in the garden is to pour boiling water on them. More specifically, into the hole in its center, the one ants come in and out of.
Before I explain any further, though, I feel you really ought to consider whether you really need to kill the ants, because most ants are harmless or even beneficial. Of course, there are exceptions (fire ants, European red ants and other imported species, for example) and even “good ants” can be a problem under certain circumstances. I recommend you read the blog “Help! Ants are Destroying My Lawn” (a somewhat satirical title, I must confess) before acting.
If you do decide that, in your specific case, the ants really do have to die, will pouring boiling water on the nest help?
The answer is: sometimes.
That’s because even water at a full boil cools down rapidly in contact with the soil. If the queen of the little ant colony is just under the surface (and to destroy an ant nest, it is imperative to kill the queen, because even if you kill 100 worker ants, if the queen survives, she’ll just produce more workers), the water may still be hot enough to end her life and then, yes, the nest will be destroyed. If she has wisely installed her nest deep down in the ground, however, the water will probably have had time to cool off before reaching her.
You’ll know soon enough whether the treatment worked or not: if the nest is quickly rebuilt, the treatment didn’t work.
Note that you should use boiling water with discretion, since it can damage surrounding plants. Thus the boiling water treatment is one you’d more likely want to apply to a terrace where ant nests have cropped up between the paving stones than to a lawn, a flowerbed or a vegetable garden.
A Better If Slower Method
A more successful (but much slower) way of controlling ants is to put out ant traps or to create your own (a half and half mixture of boric acid [or borax] and icing sugar poured into an empty soft drink can makes a great home-made trap). It can take two weeks or more to kill an ant colony with boric acid, but when the job is done, it’s done.