I only send a few items a year to Germany. Does German packaging law still apply?

Yes. There is no minimum. Registration (§ 6 VerpackDG) and system participation (§ 7) apply from the first parcel of packaged goods you send to a buyer in Germany, whatever your size. Small volumes usually mean you pay the dual system's minimum fee, not that you are exempt. VerpackDG § 6+2