Several weeks ago, I noticed six separate ant colonies have moved into some potted plants of mine: three geraniums and one dianthus I overwinter every year in the conservatory (those plants come in every October and then are put outside every April) and then in my chives and nemesia (which are kept outside year-round). It really surprises me that with the first four plants, they actually moved indoors at such a rate! One of those geraniums I've had for about 7 or 8 years now and the others for around half that time. I adore the former geranium especially (we're quite attached), even having nursed her through a bad case of edema at one point. I can tell they're sucking nutrients from the soil.

As an experiment and in using the affected nemesia, I dug my fingers down a little into the soil and saw all these ants carrying eggs. I've long had an interest and fondness for ants so it sucks I'm going to have to evict them.

I currently live in England, but come from the Sierra Nevada mountains of California. There, ants mind their own darned business when it comes to establishing home bases; they happily build their hills in the local soil amid all the pine cones and needles, leaving your potted plants well enough alone! So, this is frustrating for me in having to deal with such lazy, opportunistic, selfish, freeloading ants in these parts!

Admittedly, I had this happen with one of my parsley and lemon balm plants a few years back, but that was it. A couple years ago, I'd noticed some took up shop in two pots where there'd once been annuals and those communities are still there. I'd let those be since those plants had passed onto The Great Botanical Garden in the Sky once their time as annuals was over.

So, my questions are: how best to prevent this happening again in the future as an organic gardener? What might've attracted droves of ants indoors in the first place? I've looked for aphids on all of the above plants and have seen none. I will say that, in a pinch, I had to use some Miracle Gro (in part) when replenishing the soil for most of these plants last summer so don't know if that might've attracted them, but it seems like a possible common denominator.

Before, when this happened with the aforementioned perennial plants of mine, it was fairly easy to deal with as the colonies seemed to just be getting started. I uprooted the plants, emptied out the soil and ants along with it, washed down the pots and put in fresh, new soil prior to re-planting. With these newer ant colonies, they seem more established (I hadn't noticed them until earlier this spring so don't know when they all moved in since the winter is a rest period for my 'girls.').

I'm not sure how to deal with eggs, queens, etc. I'm quite a sentient person so I'm going to feel awful evicting them, but it's obvious they're affecting the overall health of several of my long time plant babies which leaves me no choice.

Ugh, this is going to be so much work; I'm not looking forward to it - not at all. And as I'm the only gardener in this household, I'll be dealing with it on my own. Aye me.

Thanks for any advice; I greatly appreciate it.

Ants try to come into the house every fall and every spring... and they love setting up house in my plant containers! The best defense seems to be a good offense, and I use gel bait stations from brands like Combat & Terro. You can also get the gel in a sort of syringe that I use to refill the otherwise single-use stations. I've also discovered that Ortho Home Defense spray is effective if I use it across thresholds (windows and doors) where ants might enter or along any obvious "highways" they are using (like along the kitchen baseboards.

I doubt you did anything particularly to attract them other than having nice loose potting mix for them to colonize. The tiny ones will set up housekeeping anywhere... I once found a colony under the edge of my kitchen sink, between the metal sink and the countertop.

They can be fascinating to watch outside, but they are so numerous in this area that I don't worry about trying to "evict" them; I just eliminate them if they come inside. They kept moving from one seedling flat to the next this spring, and I just kept moving my bait stations until the colonies had been killed.

I realize my suggestions may not be compatible with your desire to garden organically, but I've had better luck with these methods than with putting down Borax mixed with powdered sugar (pretty sure they just eat the sugar). Another suggestion I've read is to sprinkle grits or cornmeal around, that eating this is somehow fatal to them, but I believe that's also a myth, or at least it doesn't work on the ants here!

Greetings. I had a Cornish nanny and know a bit about the area. I visited once. As England goes it has a good climate for gardening.
I don't know if it's available in the UK, but here there is an ant bait containing the organic insecticide Spinosad. It works OK.
For a few pots I would consider immersion in water (above the rim of the pot) for several days. I put a bit of Safer's Soap in the water. Do this outside. The ants will be evacuating to the nearest convenient spot.
Cheers.

Yes! Somehow I missed that you had ants in "only" six containers... Immersing them in water (even just for 24 hours) should do the trick. When the ants start moving the eggs, the queen will likely be evacuated also.