Should i still practice snowboarding if i suffer from lumbago?

Depends: I would recommend checking with your physician first if its safe for you to do. Remember to stretch, and strengthen your core muscles prior to the season.

As long as you note : The pain does not interfere with your activities it should be fine. You may want to consider a more focused exercise program aimed at core stabilization and flexibility with some cross training in terms of cariovascular exercises.