I have a large older indoor Jade plant with the main trunk being 28″. The pot size is 53″ at base. Minimal west light during the winter and has not been repotted for at least 15 years. The new growth is spindly and falling off and the branches that do fall off are mushy on the inside. When watered there is a moldy smell. The moldy smell came a few months ago after trying to add some soil to the top. This plant has been to new homes at least two times before I was blessed with it. It was it’s healthiest a couple years ago when I was able to keep it outside in the PNW on our deck for the summer where it received SW light. I’m assuming it will need to be repotted along with any other recommendations you may have. I would like to know the best way to repot it, as it’s quite large. I would SO like to save it!
Older Jades have very minimal requirements that must respected. They do not like change or to have their roots disturbed or to be repotted. The moldy smell is caused by the soil you added. There was no good reason to add the soil and several good reasons not to do it.
First, the quality of the soil you added may not have been a appropriate. Any soil used with plants must be sterile and disease free. One cannot just use any soil. More importantly, the soil added on top retains moisture and keeps the soil around the roots from drying out sufficiently. That is causing the roots to rot and the stems to turn mushy.
You must remove all the soil you added immediately! Then, you have to allow the original soil to dry about halfway deep into the pot before adding any water. I hope that it is not too late for the drying out to occur. That is the only cure for root rot. Various remedies such as changing the soil or adding fertilizer or peroxide are completely off base. There are no quick fixes here. Just let the soil dry out. Abundant sunshine and warm temperatures will help the drying out process.
Any long stems and any soft stems should be pruned off. Jades need to be prune regularly in any case.