Time.

As for the individual plants wilting, check the moisture content of the rootballs. Too wet or too dry?

Wet.

I have killed more plants by over watering! It's easy to do.

Since winter is just around the corner in your part of the plant... I'd do nothing until Spring. Let the leaves alone...they will probably blow away before the snow hits.

And perhaps think of a plan of action over the winter to rid your property of that useless landscape fabric.

Was organic matter added to this soil before the fabric and mulch was applied? 5 inches of mulch an a good healthy soil, well endowed with adequate levels of OM is not too much and will not cause compaction of the soil, but that same amount added to, especially, a clay soil that has not been amended properly can cause compaction.
Something too many people seem to forget is that plants roots need about as much air as they do water and too much water will exclude the air those roots need. There is not much you can do now (not enough time) for that soil, but next spring plan on removing everything and amending that soil with organic matter.

Time, and addition of organic material to the area. If you search the subject of landscape fabric on this forum you'll find that many people have had problems with it. No personal experience with it, though.

The only alternative I see to save existing plants is to transplant those plants to another, better drained area temporarily. That is, assuming that your weather will still permit it. I'm still transplanting like crazy here in Ohio.

Karen

Unfortunately clay has this amazing ability to retain moisture.and keep it there sometimes if the top inch or two starts to crack.

Now that being said, I am betting that the area thats getting all wilty like is going to be a low spot.

Here are a few suggestions:

1. ammend soil with BOOKOOH!! Organic matter
2. After Halloween there may be some straw bales waiting for the city pick up. Hay is a carbonaceous material, that has the nifty benefit of being able to infuse the soil with much needed porosity ( breathing holes for moisture and air to circulate.) if you can get a bit of that stuff in the planting hole that may be able to help.
3. move plants to a higher or drier locale, if the position of your plant is not too important.
4. if you have lots of money and time, you can try adding sand to your clayey soil ( talking truck loads here).

Looks to me like the landscaper didn't do anything to improve the soil before covering it with the cloth and mulch - and so made a hardpack clay condition even worse. That water cannot escape because of the mulch cover and cloth cover.

Solution - I agree with ixnod's suggestion on soil improvement. I've broken up clay matter by adding loads of composted material and also used builder's sand (fine sand will turn the clay into cement). I also did the job myself one hole at a time. Clay soil finally improved. With organic matter in place, the earthworms will also help in improving the soil.

So in my opinion, remove the fabric, get going with the soil improvement. Of course move yoru plants temporarily for the winter (which means pot them up and imbed them in the ground, and mulch for witner protection)

Once soil improvement is done, try to see why a landscape fabric was placed in the first place. For purely decorative reason? Or to help what is normally a dry spot or weedy spot?

Should I be raking back the mulch, cutting out the fabric and putting in a ton of compost and peat?

On the subject of peat.

Definitely a no no in this area. first peat does not have any real nutritional value when it comes to feeding the soil or the plants. in windy conditions the Peat will blow away once it is dried out. getting it wet can be a chore in and of itself, you have to be either A: Patient with watering and setting, then watering then setting while its still inside the plastic bale. ( a bit entertaining to see it expand. although wet Peat is also HEAVY ) or a wetting agent. A gentle hand soap will break the tension on the water and act as a surfactant
B: crazy, if you mix it all in, the Peat will rise to the top of the soil and/ or compost and look all filmy like. then it will blow away in the wind.

so the lesson to be learned is Peat moss will do you no real bit of good for your wallet, your plants, or your soil.

by what you have said you have simply over watered, 5"s of mulch isn't too much with an as required watering regime, our mulch is commonly around 8"s thick, this so we can water less.

clay doesn't drain well, so all you can do is wait for that to happen, which coming into your winter could take a while i'd suggest. the landscaper should have suggested a raised bed type situation over the clay this would have helped, and i'm no fan of fabric ever.

so maybe sit it out over winter then replant next season but with a "water as required" regime, depending how dry and hot it gets where you are, that may be once a week or even once a fortnight.

len

Here is a link that might be useful: len's garden page

In your situation I would be gathering and shredding all the tree leaves I could find. These can be composted after shredding, and will be ready to dig into the high-clay soil in the spring. We use a gas lawnmower with a mulching blade to shred leaves. Its fast, and we already own the mower. It will take several years for you to make enough compost to cure your problem with slow draining clay soils. But, the results are worth the effort, as long as you intend to live there for a decade or more.

When you mention "irrigating", are you in an area where farmers irrigate, with lotza water?

I mention this because I live down half way down a long, 3 mile hill where everybody irrigates either through side rolls, or flood irrigation. Half way through the summer, I start getting spots around the place that are going to be wet until the ditch water is shut off. Then, they dry out in a couple of weeks. And this is clay soil as well.

Everyone, except the guys on the top of the slope, has this problem. I'm actually going to put in a few hundred feet of 4" French drain pipe in one area, because it just won't dry out in the summer.