Dragon trees should be repotted during the spring or summer. They actually like to be slightly root-bound, so they don't need to be repotted too frequently.
When should I repot my dragon tree?
Repotting: Repotting should be done about once every two years or so. If they become root bound growth is likely to be very slow. You can check the bottom of the pot to see if roots are appearing through the drainage holes and if they are the plant is root bound.
Should I repot my dracaena?
Set up your dracaena in a fair-sized pot filled with special indoor plant or green plant soil mix. Although it may be necessary to repot it in spring every 2 or 3 years, when not repotting then go for regular topdressing which should also perfectly answer the growth medium needs of the plant.