Some weeds need light to germinate, to start growing. All plants need light to keep growing. Even perennial, deep-rooted weeds like dock weed will exhaust their stored food supply and die if they cannot photosynthesise because light is excluded.
Mulch does a good job of excluding any light; it also stops wind blown seeds from reaching the ground and rooting. Mulch however will not stop deep-rooted weeds from growing through it.
The mulch needs something underneath if it is to have any chance of stopping dock weed or dandelions. Weed control fabric is designed to do that job. It does so very well, but weed control fabric allows wind blown seeds to put roots down, through it, to the soil. These weeds cannot then be removed by hoeing, because the fabric stops the hoe cutting off the weed just below ground level.
landscape-paper is a new, lower cost, alternative to weed control fabric.
You roll out the landscape-paper onto your vegetable or flower garden. You cut 3 inch diameter holes in it and plant your annuals, cabbages and onions through the holes. Cover the landscape-paper with mulch and you have an attractive looking and totally weed-free vegetable garden or annual border.
landscape-paper comes in rolls 3 feet wide and 25 feet long. It is a pale brown color and it is biodegradable. The paper only lasts one season, but its low cost means that replacing it next season is no big deal.
For those who are growing organically landscape-paper is certified as suitable for growing organic vegetables because it contains no bleach or artificial additives.
If landscape-paper is not available where you live there are similar alternatives you might consider using.
Woodchip wallpaper is the first alternative, low cost, non-bleached paper with splinters stuck in it. It will cover the ground in exactly the same way and rot down into the soil after a year. Wallpaper rolls are only about 2 feet wide though, so by the time you have done more overlapping than with the wider landscape-paper your savings will be minimal.
The paper underlay designed for underneath carpets might be a better alternative. It has no splinters in it and it is usually 6 feet wide, meaning less is wasted through overlaps.
Sheets of newspaper will also do the same job of separating mulch from soil, but these will not stop deep-rooted weeds in the same way as the others will. Use color printed newspaper if you want them to rot down more slowly.
You can also use newspaper sheets where you are laying turf. Just put the newspaper down on top of the raked soil. Weigh them down with stones and leave them for a month. Most of the weeds will have died by the end of the month and you can just roll the turf out on top of the newspaper.