Thank you for contacting Ask Extension. It sounds like your Back in Black Sedum plants are experiencing some issues. The symptoms you're describing, such as branches breaking at the base and the plants drying up and dying, could be indicative of a few different problems.

First, it's important to ensure that your plants are receiving the right care. Sedums, including the Back in Black variety, are succulents and can be sensitive to overwatering, especially during their dormant period in winter. Make sure you're allowing the soil to dry out between waterings and reduce watering frequency in the fall and winter. I am not sure how long ago they were planted, but pull the mulch back 2-3” from the center of the plant. That alone can cause stems to rot and the crown to have issues.

Additionally, if the plants are not reaching their full height, it could be due to insufficient light. These plants thrive in bright, indirect light, and if they're not getting enough, they may not grow as vigorously.

Lastly, if the branches are breaking at the base and the plants are dying, it could be a sign of root rot or other root problems. You can notice that most of the stems on the broken sedum are hollow. Hollow stems in sedum can be caused by a variety of factors, including poor soil drainage, overwatering, and exposure to excessive wind or sun. The hollow stems can also be a symptom of a fungal disease, such as anthracnose, which is characterized by circular, sunken, pale, or brownish spots on the plant tissue, where it dries up and becomes hard and bark-like. If you're experiencing hollow stems in your sedum, it's important to ensure that the soil is well-draining and that the plant is not overwatered, as this can lead to root rot and other issues. Additionally, providing good air circulation around the plant can help prevent fungal diseases. Root issues can affect the plant’s ability to absorb water and nutrients. If you want a MSU lab diagnosis, you can go to Plant & Pest Diagnostics (msu.edu).