how to save a betulia for next year

They need somewhere frost free and dry as they will die donw to an underground corm/tuber like bulb. Start to cut back watering and wait untill it naturally dies down, cut back dead foliage and leave somewhere cool, frost free, but not warm, and dark.
Pot up next spring and water sparingly at first around april time, gradually increasing as spring comes to a full.
Over watering will cause it to rot. To little is better during early spring, but water as norm whan shoots appear.
Then continue as you have been