Hi hayleybritt and welcome, I'm not one who likes to use weed barrier liners. In my experience, they make more work than they save. You could give old sheets or other fabrics a try, but my feeling is that you would be better served not using them. In time soil blows into any mulch you may have used on top of the fabric - then weed seeds can geminate in that soil/growing medium. The edges of weed barrier can "float" up over the course of a couple of seasons and then you have all this fabric sticking up all over the place. When you go to dig in the area (move a shrub or install a new planting) you end up pulling the fabric up here and there and it can turn into a mess. I guess I prefer to not have a layer of fabric in my soil - it gets in the way of things and often ends up looking bad. If I were going to use a weed barrier I'd want to use something durable - I think old sheets will degrade pretty rapidly and then you will be stuck trying to dig it all out to clean up the mess. Those are a few of my thoughts on the matter. Perhaps others who like to use weed barrier fabrics in their garden beds will chime in with some other opinions. Have fun, Chris Here is a link that might be useful: a link I found from a gardener who recommends against using weed barrier fabrics

I use 5% strength white vinegar, from the grocery store, to adjust the pH of our tap water when its necessary to irrigate the blueberry shrubs. It takes 6 fluid ounces of vinegar to treat 4 gallons of tap water. I would never use full-strength vinegar to kill weeds unless I was certain that I was far enough from the roots to avoid damage. In your situation, I would pull the weeds by hand. That's exactly what I do, every two months or so.

Duckweed has a high content of protein meaning it has lots of nitrogen and is a great replacement for grass clippings. I'd add a dried carbon source to balance the nitrogen out. When I have a lot of duckweed, I use it as a green mulch around my tomatoes. It is great for weed suppression and moisture retention. In about a month it begins to break down and adds nitrogen to my plants. Then they take off! I write about how to source, grow, and use for duckweed for many uses. Duckweed rocks! Here is a link that might be useful: Duckweed Gardening blog site

I think that you are going to have a wildflower garden that includes some of the grass that was there before you planted. There is probably no way to get rid of it now, and even if you did, it might just move in later. you'll have to accept this, which means you don't have to worry about pulling up all the grass. I would instead try to make sure that really noxious weeds are kept out, and keep pulling larger weeds or trailing grasses which seem ot be crowding out wildflowers. Things like Canada Thistle, Spotted Knapweed, and similar invasive plants that could really take over should be killed. You can pull out the larger clumps of grass, but probably most of the wildflowers will be able to coexist with grass pretty well. I am assuming that the grass is one of the common exotic pasture or lawn grasses - orchard grass, timothy, etc. Eventually you should be able to have a mix of wildflowers, some grasses, and some weeds that still gives you the look and feel of a prairie despite the presence of some non-natives. Keep in mind that it would be almost impossible to have zero non-natives. You are instead trying for a balance that includes all the flowers you want and not too much stuff that you don't want.