Two Quotes from Google:

'Borax is not safe to ingest.... '

and

Borax can be irritating when exposure occurs through skin or eye contact, inhalation or ingestion.

However, you are talking about a topical thing in your garden, so I doubt the plants grown there would pass on any of this toxicity. Just make sure you rinse your produce before eating... which you probably do anyway.

As to ants on your plants: I sprinkle liberal amounts of Diatomacious Earth around the base of plants. (Which reminds me that I need to do a new layer under the potted Meyer Lemon Tree.... on which the ants like to 'farm' their Aphid and/or Scale 'cows' - from whom to get the Honeydew to take back to the nest to feed the Queen.)

I'm wondering how well that worked, H P? Are the ants gone?

And you could simply water the area very well to dilute any lingering borax. I'm not sure it even poses a problem outside like that, unless you're digging in the beds barehanded and licking your fingers...?

Borax is mined from the earth, I believe.

@carolb_w_fl_coastal_9/10 it worked fairly well i think it might have taken a couple of applications (i only did the one) but i saw far less activity from the ants for about a week or 2. Thabkfully mine are the little brown lawn ants that dont bite

@CA Kate z9 i have DE but i disnt think to make sure it was food grade when i bought it so i only have been using it outsideof the beds

DE isn't something that I would think is Food Safe.... or not. It isn't a poison. It won't contaminate your food any more than blowing dust would. It is made of teeny-tiny crystals that damage the ants'/insects' bodies... and they die. When you wash off your vegetables any DE that happen to get on them would also be washed away.

Yes. Food grade DE is for eating, so as long as you're not ingesting the DE - and some people want food grade for use on and around pets - it should not be a problem.

But when it gets wet, it won't work any more, so using it outside is problematic.

Hot soapy water can be a good remedy for anthills, BTW.

I have learned something today: One can actually consume DE. WOW! Not sure I will be doing that anytime soon, but I'm sure some people do it for good reason.

I think it's used as an ingredient or additive in food production, not something you consume by itself.

IIRC it's just fine silica, the tiny exoskeletons of microscopic plankton. So, just sand in a very fine powder form.

Things that go in the garden don't have to be food grade. You might be shocked at how many microbes there are in a teaspoon of soil, and how many of them can potentially cause disease or infections in humans. This is why we don't eat dirt. Amazing how that works. :-D

Oh, back to the original question: Boron in excess amounts in soil can inhibit the growth of plants. So you probably don't want to be adding 'a couple of quarts' of sugar/borax to your beds on a regular basis.

I'm not even sure if ants actually cause any problems for plants. If you have aphids, they may be farming aphids. Insecticidal soap (also harmless to humans) will help with that.

We have some ants here that infest plant containers and definitely impact the roots. They will sever roots as they make their tunnels.

The trick to using Borax for ants is to make a solution that is strong enough to kill them but not so strong that it kills them instantly and they never bring it back to their nest. You can soak cotton balls in the solution and place them in short pieces of irrigation tubing so the borax doesn't go into the soil. 1% concentration is good for outdoor ants. http://ipm.ucanr.edu/PMG/PESTNOTES/pn7411.html

Using a product called "Terro" that works great to get rid of ants, it's basically the same thing (boric acid in sugar syrup) but they formulate it right for their job. I usually place a bottle cap of it near the ant hole, works good inside and out.

I use Terro liquid too, but it just doesn't work on some ants - the ones that aren't interested in sugar.

We get tiny kitchen ants every spring, and Terro works great. You have to be a little patient as they suck it up and carry it back to feed the others, but usually within a day or two the infestation is gone.