i was saying that because its in the gardening section, we use wood cxhips as mulch on our veg plots, it keeps the slugs down too, but it rots down beutifully into soil without causing problems.
the ground cover crops are great too, they put more into the soil in the way of nutrients
why did you not fill the pots with soil to the top? you need to carefully tip those out into your hand, seedlings in the gaps between your fingers, so as not to damage them, then put them into new pots of soil.
one to a pot, you may have to sacrifice one of the seedlings in the pots with two...
weed supressing fabric, the heavy duty black woven one works best, then cardboard, then another layer of black weed supressing fabric, give it a year or so ,ans voila, no more weeds, then just use wood chips