you planted it 2 weeks ago.. in MI ... was it 100 the day you did it???

if so.. its because you planted in mid august.. no matter if the water was perfet.. you stressed the bee-gee-bees out of it ..

if i misread your facts.. you need to clarify it

ken

I've had that happen before where a sedum will rot out at the base and the leaves slowly die and drop from bottom up. Usually it happens when I plant them in areas of the garden that don't have SHARP drainage. I've saved a couple by quickly moving them to gravel-y areas of my garden that drain easily. It could be that your clay retains the moisture awhile after you water. The burn could be from simple stress.

I don't think planting bulbs amongst the tall sedum would work. My sedums are early to rise and dense by nature, so I think they would crowd out the allium before they had a chance to get growing.
CMK

I agree that Sedums need excellent drainage. Either rework the soil base or plant into oversized pots with well draining gritty soil mix and plant pot and all into your clay soil. I would underlay the pots in the ground with a 4 inch layer of gravel for additional drainage outside the pot. Below is an old pic of a low growing native species that has grown to fill in the bare spots and over the sides at this writing. Note the gritty soil mix-granitic gravel-available from landscaping companies.
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The sedum were planted right after the heat wave ended so maybe less than 2 weeks ago. It has been hot the last 2 days though.

I think the drainage is the problem and its starting to rot......will have to dig a larger hole and amend the soil.

These root easily. Take a few cuttings to keep them going.

I think you could tuck the giant allium next so some sedum. The foliage on these types of allium die off and the sedum would take its place.

There are 3 general causes for sedum to rot like you mentioned. 1) Yes, excessive moisture can rot some stems, and they like good drainage, but they are tough and can tolerate a very wide range of conditions and this is the least likely direct cause but can lead to fungal problems. 2) They do not like excessive fertilizer and can suffer from fertilizer burn. If you used any kind of fertilizer at planting time, or used miracle gro or other water solubles then you could have burned the stems. 3) The most common problem I've been seeing in sedum over the past several years is stem rot from water molds and fungus. Phytophthora and anthracnose appear to be somewhat common, and they are more common in poorly drained conditions. Destroy plants that are really bad and treat the area with a broad spectrum fungicide to control the spread.

Thanks, I am going to try amending soil to improve drainage

Lots of minor spring bulbs will do well around larger sedums. They like the somewhat dry conditions that sedums favor. However, most of them bloom quite early in spring and are quite short. I would suggest Ipheions, Chionodoxa, and Anemone blanda. They bloom when the sedums are just small green cabbage like nubs low to the ground. They also have quickly evaporating foliage. Taller possibilities would be Fritilaria meleagris or miniature daffodils, such as Tete-a-tete. Both of these have larger and somewhat more persistent foliage. All of these have done very well for me in the drier areas of my zone 5 clay soil gardens.

I have found that Scilla, Muscari (Grape Hyacinths), and to some extent crocus, are a little too aggressive for interplanting with perennials, but do well for paths or around shrubs or sub-shrubs.

I do have a ring of Sedum alboroseum 'Mediovariegatum' (a mid-size variegated sedum) in front of my planting of Allium Globemasters & giganteums, originally 6 plants I think, with golden pennywort, Lysimachia nummularia Aurea for groundcover. The dryness of the area helps keep the pennywort in check. However, the sedums are not really big enough in early June when the big alliums bloom to hide their foliage well. Keeping with the yellow theme I also have some originally self-seeded pale yellow echinaceas in this area and some small pale yellow daylilies. The daylilies seem to do the best job of hiding the foliage of the alliums.

BTW, the large alliums are not all that persistent for me so I usually add a few every couple of years to keep the stand going. The sedums are a little brittle to crawl over, kneel down, or even to get your feet situated to use a standing bulb planter to plant the large allium bulbs. So I would suggest leaving a little path behind the sedums to work in.

One more thing - though I really love my Alliums & Lilies - little minor bulbs are so much easier to plant and they also do really well in shady areas around trees & shrubs, since they pretty much come an go before the trees leaf out.

I have the type of sedum you are growing in my garden. They are growing with Daylilies, Spring Bulbs etc. They are a full sun good garden soil plant.

I do not see any reason you could not plant bulbs with your sedum just not under them.