I read this topic on here about 3 months ago and decided to give it a try. In the last few years my wrists and certain finger joints began to ache 24/7. I'm in my early 50's and always have been very fit, active, and health conscious and know my body very well. I also have suffered from osteoarthritis in my lower back for decades due to injury.
I started with 1/4 teaspoon of borax in my morning shake after workout. Drank my normal 2 litres of water by lunch and then added another 1/4 teaspoon to plain water for my afternoon 1.5 litres.
Within a week my wrists and fingers were about 60-70% better and I could feel something happening in my back and knees. At first there was some different areas of mild discomfort (and this is expected as the calcium deposits break up) and now they are pain free after about 3 months. There are many other positive health effects with boron supplementation as well as antiviral, anti-fungal plus anti-tumour properties. Check it out:
I think the boron is bound differently in soil, It might not just there as borax. I don't think it is quite that easy to repair the soil because it'll kill the small creatures before it gets bound.
I'd experiment before just watering your garden with it.
depends on volume, you don't need alot to have it start breaking down naturally in the soil. Too much of anything is bad, however if you can find a sweet spot there might be benefits.