I do change things out a lot, and when I do I'll add more compost. I like partially decomposed wood chips as an additive...maybe 5%? Not much, just a little. Usually I just turn under last year's chips...if there are any left. If I feel I don't need to change it out entirely I just top it off with fresh compost, and then as a moisture-retentive/compaction reducing mulch I'll add new wood chips, pine fines, crushed limestone or pebbles ...depending on the plants' preferences. Same as in the gardens...just on a smaller scale.
Greene. The only time I have poor drainage problems in pots is when the worms aren't active.
