Is it the soil or the light requirements for clematis like cold feet and warm head?
I would take a soil sample if you had adequate light, with some ground cover for shading the roots.

Contrary to popular folklore, clematis do not like cool feet but rather what occurs similarly where they have cool feet--that is moisture. Clematis can do marvelously well in containers in my zone where the containers warm up very much in the summer sun provided they have adequate moisture. Mulch will work to provide the moisture barrier and keep the roots moist. Plants that are planted as ground covers over and around clematis will act as moisture barrier and shade the roots but they will also draw moisture out of the ground for their own needs.

If they have died, it is likely from getting too dry. As long as you keep the new ones moist, there should not be a problem. There should not be any disease in the soil.

Plant new ones deeper than they are in nursery pots, pinch them back and keep them well watered and fertilized.

Here is my dilemma, these 2 clematis were planted on a slight slope, with a fence behind, clems on the south side. On this same slope, there are 5 others growing nicely. One is over 40 years old. There are 2 holes close together, the requiset 2 ft square. I always try to plant following all the rules. I'm now beginning to think they died from drowning. when I dug these holes there was a lot of clay at the bottom which I punched holes in, and added some old bricks. Then old manure, compost, and some bone meal. There is a soaker hose running next to the fence, as this slope drys out quickly. I'm wondering if I drowned them. When I dug to see if the clem was really dead the soil was really wet, and maybe because of the clay bottom to the holes they didn't drain right. What do you think? These were nice plants( from Joy Creek ) but neither one ever did much. both # 3's.

Flowergirl, except for clematis crispa which is sometimes referred to as bog clematis, clematis do not like to sit in water. If your planting hole was full of clay and you dug a 2 foot square hole and amended it well, then you in essence planted your clematis in a swimming pool that collected water when you watered or it rained. I think, like you, that most probably the clematis rotted due to too much water.

In my garden, I have high clay soil. As a result, if I am planting a clematis, I add a little soil conditioner to the hole and mix it with the native soil. I do not go overboard augmenting the soil because I know that I will end up killing clematis due to the swimming hole effect. I then add compost, horse manure, or any organic material including grass clippings around the plant (this might be more grass clippings or wood chips/ground hardwood mulch. As these materials break down, they will add organic matter to the soil but not give you a swimming hole for the plant to sit in.

If I am preparing a large bed or raised garden area to plant clematis in, I go hog wild and add all sorts of amendments since the larger area will drain well and not cause the problems associated with planting a clematis in a hole that has been overly prepared.

Certainly they can rot as well as die from getting too dry.

I also garden on clay but after adding compost as a top dressing for over ten years it is much improved. I never dig out the recommended amended holes as I've always thought the root growth would stop at the edge of the amended zone and effectively make the plant potted not in the ground. I've had very good luck and now most universities do not recommend amending planting holes. Planting beds, yes but not individual holes.