I had this dracaena for at least three years. Now I have been having problems with it. In these last 3 months leaves started turning yellow and dropping off and then even the green leaves started to fall. The tallest branch will soon end up with no leaves. I water it only once in a week and am very careful not to overwater it.
You think you are not overwatering, but I am not so sure. Your pot is in a cache pot. When you water do you take it out and let it drain before putting it back in the cache pot? Or empty the cache pot after water has drained in to it? If not it is sitting in water and is over-watered.
What is the soil like that it is in? Dragon trees need quick draining soil, like cactus mix, not like ordinary potting soil.
Have you repotted it in the three years? If not, it is probably root-bound and your soil is breaking down.
I agree, it sounds like too much water and probably could use more light. Dracena marginata is a variegated plant. As a rule the less green in the leaves or more variegation or other color, the more light it needs. Chlorophyll is highest in the green leaves.
I am surprised that you are having problems with your Dracaena. They are fairly bullet proof. You may be loving your plant to death. DITTO RBG and Imafan on the issue of water retention in the cache pot and the possible need to pot up in fresh soil.
I have a HUGE Dracaena on my patio. It is currently in a 24" pot. I pot it up every 3 years. The last time was 2 years ago - spring. In the process some of the branches broke. I stuck them in pots and they are now 3' + tall. There was a small piece - 3" - that I over looked. It was hidden in a bunch of pot shards. It sat on my potting table through winter with no soil. The following spring I found this little piece of trunk. It had roots and leaves, Stuck it in a pot. It is 2' tall.
Looking at the diameter of the pot in relationship to the height of the plant it could be root bound. There is also the issue of standing water in the cache pot as RBG pointed out.
Gently remove the plant from the pot. Inspect the roots. If they are wrapped around the root ball they are root bound. Unwrap and snip the roots. Loosen the soil.
If there are few roots and they are mushy then you have root rot from excess water. Gently rinse away the soil from the roots. Trim off mushy roots then repot in fresh soil.
