What is the cheapest and most effective ground cover and weed blocker for a large area? I am using black weed blocking sheets but they aren't terribly effective. I'm not sure how to proceed. I'm thinking tiles, stone or possibly mulch over the weed blocker, but I know it won't be cheap. Any ideas?
You're on the right track with the sheets. Try a double layer if you are thinking of using this under a gravel mulch. The mulch should be a minimum 100mm deep.
If you would prefer plants to take over instead, there are many effective species but it does depend on where you are, and what environment it is (ie sunny, part shade, frosts, soil quality). Do you have a photo of the area?
If you are trying to kill most everything that is already there, before starting fresh with seeds of a groundcover or grass which will grow in thick and not allow any weeds, You can cover the entire area in large sheets of black builders plastic and solarize (bake in the sun)the whole area. It will take six weeks, more to be safe, and the neighbors may think you have lost it. Water the ground heavily before you put the plastic down, (the heat and moisture should make everything sprout that's down there) and wait to do this until its hot, which should be no issue in Utah. I have not found that 'weed barrier' is effective, as anything that is permeable to water, which it has to be to have any plants at all, Is eventually permeable to sprouting plants as well. A really thick layer of gravel is about all I have seen to really prevent weeds, but good gravy is that an ugly solution. Find something that will grow thickly and do some work to get it established, pulling invasive weeds till it fills in, then you should be able to enjoy your outdoor space.