What kind of soil? I use soil-less mix like Pro-Mix or some other major brand of potting mix, that does not have any soil in it, and has never had any weed seeds.

I did sprinkle a very light layer of sand on the top of some of my containers this year, supposed to help keep the seeds in place. There have been a few more weeds sprouting in the containers than usual, but at most maybe 2 in a container. I suspect those came from the sand.

yes pro-mix is very good, I should have stuck with that. altho it is hard to find in my area. what I bought from the nursery is what they buy in bulk from canada and they sell it at cost, so it is very cheap- like 2-3 $ for a big box. Usually it is very good. I've been using it for years, and never had any problem with weeds.

something happened this year. I'm going back and ask them to replace the soil I have left.
for the rest nothing to do but carefully pull the weeds.