I use pond water to water our gardens and to this I add a little Lugol's Iodine that I make as well as earth salts and black strap molases. I also use cayenne and oregano and if there is a fungus problem, I add peroxide.

I have found this to be all that is needed and I see no toxic effects, the plants seem to love it, but I know of no method to remove weeds except to pull them.

MH

PS
I let the pond water sihpon into a 300 gallon tank and then I pump from this tank; this allows me to add the above product to the water before pumping. ALSO, the ponds are above the gardens, so I can water with no pump pressure as well, gravity does a fair job pushing the water 2,000 feet.