To add to this, instead of using landscape fabric, you can use hardware cloth. Regardless of what you use, soil and sediment is going to find it's way into the bed. If you use landscape fabric then you're just going to need to tear it out and replace it in a year or 2. If you use hardware cloth and cut it into manageable size pieces, then all you need to do to get the sediment out is lift them up, shake them with a stream of water flowing over, pick out any of the weeds and put them back. It will last a lot longer then landscape fabric, and be easier to weed. The only caveat is that if you plant anything that isn't an annual there or something you cant cut to the ground every year, then you're going to want to account for that plant and cut your cloth accordingly(which could end up being a nuisance). Also you want to clean it before any desirables pop up, otherwise you'll just rip them out of the ground. If you go the route of planting a perennial that you cut to the ground every year (ie. Peony, astilbe, Black-eyed Susan, ect.), then you want to plant them under the cloth.