I have had my Dracaena Marginata for about two years and it has two “trunks”; I recently noticed that there are cracks or splitting in the trunks. I cannot seem to find anything that indicates what is happening. I did ask my FB houseplant group and I am getting mixed Answer:s.
I have had it since it was less than a foot tall and it is beautiful now. It is not in direct sunlight ever, it is in my office which does run a little dry but the temp is about 73 year round. I did recently transplant, maybe 6 months ago and it seemed to really tolerate that well. That I am aware of there are no pests, the leaves seem really healthy and there is no dropage.
I am hoping you can solve the mystery.
The cracks in the trunk are unusual but may be related to the over-sized pot that you have your Marginata planted in.
Unnecessary repotting and using pots that are too large are the most common causes of plant failure. Over-sized pots have excess soil that acts like a giant sponge in retaining water around the roots for a very long time. Out of sight, the roots slowly begin to rot. Often, especially with Marginatas, the roots die back and the plant shows no symptoms until the roots are severely compromised and it is often too late to save the plant. The excess moisture around the roots may be causing the stems to crack to help release the excess water.
You have two options. One is to remove all the soil you added to the top of the original rootball. When repotting, you should never put soil on top of the rootball. Removing that soil will allow more oxygen down into the root zone. Then, be sure to allow the top 1-2 inches of the rootball to dry out before adding any water. Then, add just enough water so that it reaches that same level of dryness again in about a week. If the root damage is not too severe, then this reduction in watering may help the roots recover as they receive oxygen regularly.
The other option is more extreme and I am hesitant to recommend it if you are inexperienced. That would be to carefully unpot the plant and remove all of the soil your added six months ago around the original rootball. Most of that soil will be loose and will fall away easily demonstrating that it was not serving any useful purpose. Then, move your plant back into the smallest pot that the original rootball will fit into. Removing the excess soil will allow the root zone to dry out more readily. If you do this, you must be careful not to damage the tiny roothairs because they do most of the work. That is why I am hesitant recommend doing this.
I am sorry that I have exposed a serious but unanticipated problem in the process of Answer:ing what you thought was a simple mystery. However, maybe you have caught this problem early enough to keep the roots from rotting complete and losing the plant.