How do I get rid of weeds that are growing through the mulch?

The trick to keeping weeds from growing through your mulch is to put a layer of weed barrier underneath, such as a black plastic weed barrier.

Purchase PREEN. Water existing weeds, pull them by hand. Sprinkle Preen.

And together rid of the ones already there, use a simple.weed.kill.spray like.Round Up

If they are growing through mulch, I guess you also have plants growing there, too. If that's the case, what I have done, if they have started to grow, is to pull them and immediately spray the weed killer safe for plants on the stem. It seems a simple answer and maybe some will have more elaborate ideas, but it works for me. They seem to sprout overnight after rain especially and I have areas of rocks and dirt that just grow weeds and if I don't keep up with them, they can become their own garden. This year, I have sprayed killer that kills everything the second I see the tiny sprout. I am virtually weed free after a few weeks of sprout spraying. Hope that helps.

I put vinegar in a pump sprayer and it works like a charm. The acidity in the vinegar kills the weeds.

Vinegar,or if that does'nt work try epsom salt that will strangle the roots

If you put cardboard or landscape fabric below the mulch, move the mulch and see if the weeds are growing through the fabric or just in the mulch. Some strong weeds will push through the fabric, or find where the seams meet if there isn't a big overlap (some have runners also so can travel underground quite a distance before popping up) If they are through the fabric, you may have to patch or replace it.

If they are in the mulch, it's probably because the mulch has decomposed some and there is now a soil like medium which needs to be raked out.

The easiest way I found is not to dump more mulch on because the weeds will grow through,but to shovel the mulch into a wheelbarrow, and replace with new, or shovel back carefully the intact mulch (leaving any soil like residue behind).

Vinegar will also kill any thing that it touches when it leeches into the mulch and soil or over spray. This will kill anything, even the plants you want to keep and it will stay in place for a long time and prevent you from putting in any new plants or seeds.