Do you have soil, or just plain old clay? That was my big problem for years here. Once I found this forum, I discovered that you must amend the soil around here to make things grow! Tell us more.

You gave a big hint when you said, "last year 2 of the 3 Sedums seemed to rot and dye." It sounds like you may have a drainage problem and your soil needs to be amended as rizzir suggested. Soils contain varying percentages of sand, silt, clay & organic matter. Soil with a high percentage of clay, though often high in nutrients, doesn't drain well. An easy way to test is to dig up some soil, take a handful of moist soil and squeeze it into a ball. If the ball crumbles easily, then it has a lot of sand. The more solid the ball is, the more clay it contains. If it's somewhere in between, it's loamy. Also if you rub some of the soil between your fingers, sandy soil will feel gritty, silty soil will feel smooth like talcom powder, and clay will feel slippery.

You can also send a sample of soil to your county Cooperative Extension Service to be tested for pH and nutrients. They'll provide you with a bag and give you instructions on how to take your sample or you can look it up online.

Here is a link that might be useful: Another more scientific way to test your soil's texture

Thanks Rizzir and Wild Rose...
I didn't think it was a soil ammendment issue because these are raised beds that we put in when we moved here and we added good soil. Also, I use cotton burr when planting if I ever do dig into a clay area. However, I thought I'd go out and do the soil test as you suggested Wild Rose. The soil seems to be loamy--that is, it doesn't stay in a ball but breaks apart very easily, etc. However, I did notice when I went to take a sample and I moved aside the mulch to get to the soil, that the first inch or so of soil has a powdery gray all over it. Some type of soil fungus? Could it be an issue with the mulch? We used a cedar mulch this year, but last year we used a black mulch and my plants have performed no better this year.

I honestly don't know if the type of mulch you used has created your problem. The powdery gray stuff might be from the black mulch you used last year. I believe the manufacturers of that stuff use a dye to make it black, and the gray stuff could be a degradation product. It could also be a fungus which may be either good or bad. Maybe someone else here knows the answer. Instead of the kind of mulch you're using, your problem could be in the way you've applied it. If it's piled on too deep next to your plants they will suffer.

When I run out of compost I use shredded pine mulch, or even better "soil ammendment" which is actually finely chipped pine bark and sold to be worked into the soil. I use it on top of my beds as mulch. It breaks down faster than "mulch", but all the better. Check out the ongoing thread "Compost near Franklin" on this forum. There may be a good supplier of a similar compost near you that you could substitute for the mulch you have been using and get equally good results as those who have posted on that thread.

I concur . Pine straw and soil conditioner ( pine fines ) are the best . That black mulch normally has been treated with sewage and has trace amounts of petroleum distillates .I am all for reusing things , but that black stuff is horrible . You may need to try a few new plants . Stachys sometimes melts out in humidity , I have seen it look good . The airflow is critical so pull out the spent leaves . Sedum 'Autumn Joy' has been lumped into a new genus , anyways we usually dig it up and reset it every year to keep it from rotting . There are improved varieties out there . Try cuting 'Autumn Joy' back in late May or early June . This will result in a stockier plant . 'Neon' is wicked good so is 'Purple Emperor'. I don't care for Scabiosa but have seen it doing o.k. . I find that the independent nurseries have the best and brightest as far as selection .