Question: I purchased three seedlings last year and they all died during the winter. They were keep in my dining room which has a western sun exposure. The soil was a mixture of potting soil and sand. They were watered very little during the winter months
Answer: There are four things that make the plant trunk to soft: Lack of water so the plant contracts (this is normal for cactus and succulents when they go dormant), too much water causing rot, micro disease/pest of some type destroying the plant and the 3rd temperatures too cold causing damage to the plant.
Mid November 2013 a NY client ordered we sent 12 adenium desert rose plants and she went on vacation for two weeks so she was not there to receive the plants (not wte3red, planted and exposed to cool/cold temps). After 6 weeks (beginning of January) she said all the plants die and sent them back. We received the plants and they were extremely dehydrated and soft. We treated the desert rose adenium plants with Dyna-Gro K-L-N before replanting them and after 4 weeks they started to sprout leaves. They were not dead as she thought but just dormant and not treated right fro her location.The desert rose plants were exposed to temperatures considered too cold for them when the were away on vacation. But once treated properly the adenium plans survived,
You purchased seedlings. Seedlings are harder to grow especially in Northern areas without grow lights, more watering and regular fertilization than mature desert rose plants. They are much more delicate than regular mature desert rose pants. The adenium we grow from seeds are grown under much more supervision than our regular adeniums. Our young desert rose plants get fertilized monthly, water twice as much and given grow lights during winters months to prolong the hours of light they received until they are 1.6 years old and 1″+ caudex. Some adeniums plant seedlings grow faster than others due to type of adenium and quality of seeds. I would say your adenium plants did not received enough water and possible light hours during the winter. Seedlings dry out very fast because they are not large enough to hold enough moisture.