Selective weed killing in large planted beds, anyone?

We bought our house a few years ago from a man who had put in about 800 square feet of mulched beds containing mature trees, a vegetable garden, day lilies, hostas, ferns, cosmos, privet, peonies, Japanese maples, etc. in our yard. The beds have landscape fabric, soil and mulch, but over the past few years, all of that has started to disappear. I think there was probably about 2" of soil and maybe 1-2" of mulch on top of the landscape fabric originially, but now a lot of that has broken down or been swept away by rain and wind. Subsequently, weeds are completely taking over our garden. In particular, we suffer from bindweed (a rabid morning glory cousin), various grasses, thistle, and dandelion just thriving in our beds. So, we want to get rid of the bad and keep the good. But it's not like we can just get some Round-up and start spraying the few weeds we see. We need something that will be effective, easy to selectively apply over a large area, and preferably not expensive. We've considered Preen, and a Home Depot worker recommended Noxall, but when I called the company and found out it shouldn't be applied within 10 feet of plants you want to keep, we discarded that idea. We're going to put down a 4" mulch layer in a few weeks, but we need to get rid of what we've got (and it's coming up fast because this is an early, warm, damp spring for us here in Utah) and prevent more from coming before we put the mulch down. Suggestions? I'm starting to feel a little desperate.

Preen only works at keeping new seeds from sprouting, nothing for existing weeds. I personally don't think it works at all, we tried it at church and the weeds seemed worse.

Carefully spraying roundup on some of the larger weeds may work. I cut a plastic orange juice container's bottom off, push it down over the weed and spray into the opening at the top. Spray only on a no-wind day so there isn't drift.

There is no getting around it, you will have to do some hand weeding. Weed an area, put down layers of newspaper, then your heavy mulch. The paper will help keep down new weeds. This worked amazingly for us in the church beds.

Good luck.
c4

Beside what Cathy recommended, you are going to have to be more persistent than the weeds are. Most really obnoxious weeds are perennials and besides poisoning those that you can (roundup) the oblect is to keep at them until they use up there stored energy and die. Multch works becuse it blocks light from them. Pulling them up as long as you catch them as small a possible before they can manufacture more food works because they have spent more energy growing than they have had a chance to recoupe. There is also a large seed bank that need to be depleted also. Persistence is the name of the game.

Thanks for your comments - I've seen the newspaper suggestion several times, but I hesitate because our beds are so enormous. Cathy, I particularly found your orange container suggestion helpful. My husband (bless his heart) nearly eradicated my prized peonies with an out of control, frustration-induced episode involving Roundup. Oh, and I've heard from others that Preen doesn't work, but I figured we would try it and see how it goes for us. Doug, those obnoxious perennials you mentioned - our bindweed, for example - are the worst. It seems like pulling them gives them incentive to come back bigger, badder, and madder than ever. Sigh. I'll keep the persistent hand-weeding up, though. Any other suggestions for bindweed in particular? The photo below is not in our yard, but the weed is the same.

I've had good luck with corn gluten as a pre-emergent. The trick with it (and any other pre-emergent) is to get it applied in time before the weeds start to sprout, and repeat applications throughout the weed sprouting season. If you have a lot of rain you'll have to reapply, and if you have different types of weed seeds that germinate at different times, you'll need multiple applications to make sure you stop them all. I have a huge weedy field behind my house which has a lot of annual weeds, so normally the bottom terrace of my back garden would be a horrible weedy mess by this time of year, but this winter I've been good about sprinkling the corn gluten down there about once a month, and even though we've had a much rainier winter than usual (which would normally translate to more weeds), I have way less weeds than usual in that area. Other parts of my garden where I didn't use the corn gluten are weedy as usual. To Doug's point though it won't work on perennial weeds, so if most of what you've got are perennials then it won't do as much good (although they still make babies by seed, so you can still prevent new ones from coming up even if it won't help for the already established ones)