Ants Are Taking Over My Garden. Help!!

My greenhouse looks like it is the meeting point for ants from all over Europe and far abroad. They're simply everywhere. I need to find a way to contain the population. Tips are welcome!

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Invasion Of Ants

I've been dealing with loads of ants in my entire garden for a couple of years now. But this year, it's definitely a lot worse than before. It's the worst in my greenhouse. Everywhere I look, I see those creepy little creatures, working their asses off all day.

I don't mind a couple of ants, but this is getting out of hand. Whatever I touch, I get a bunch of these creepers on me. IEUW!

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Ants And Aphids

When doing some research on the internet, you find a lot of people saying that ants won't hurt your plants - but there are just as many people saying they do.

I know I'm partly responsible: I have aphid-trap plants like Nasturtiums and Marigolds all over my garden and in my greenhouse. Since ants have a symbiotic relationship with aphids, I could have expected even more ants to appear. The thing is: the ants were there before the plants were...

Ants and aphids coexist in a symbiotic relationship that benefits both species. Ants protect aphids from predators, such as lady bugs and wasps, and aphids secrete nutritious honeydew for ants to eat. ^Source

What seems like millions of ants are happily climbing the straw I used to mulch my gardening beds, hundreds at a time.

I've been looking all over, trying to find their nests, but so far, that hasn't been a success. No nest to be found.

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Organic Solutions

Last year, I tried almost everything. In the end, something must have worked, but - silly as it may sound - I don't remember which of the many methods I tried finally paid off.

So I'm back to square one...

So I started trying out every (organic) trick in the book again. I do need to make sure I won't harm my plants, though. And now that my tomato plants have started to bloom, it got even more difficult to find an adequate solution.

Here's what I've tried without any result::

Powdered sugar and baking soda
Spreading fresh Garlic
Planting garlic cloves
Spraying with essential oils of peppermint, clove, lemon and tea tree
Cinnamon
Spraying the soil with neem oil and organic soap
Spraying the soil with lava rock dust

They don't seem to care about the companion planting trick either. I had put a peppermint plant in the greenhouse yesterday and this morning I found it covered in ants. They are supposed to hate peppermint!

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I've been reading about the use of diatomaceous earth. I guess I could cover the soil with it (covering the plants is not an option), but I remember I've read somewhere that it stops being effective as soon as it gets wet. Since my gardening beds need watering regularly, I feel like I'm going to need tons of diatomaceous earth to get rid of all the ants.

Other options I found online were the use of coffee grounds and cotton balls soaked in lemon juice. Since we don't drink coffee, nor lemon juice, I thought I'd ask if you have ever tried one of these before. I'm sick of spending extra money on 'solutions' that don't work anyway.