I do not know where you live, but after flowering mine usually keep their leaves for about 8 months. I keep them outside, except for the winter months. When autumn arrives, I usually stop or slow down the watering. As the weather cools, the leaves will start to wither. I leave the leaves on until they are dead and then cut them off - the bulb will re-absorb nutrients from the leaves as the leaves die. Then I bring them indoors before we get the first hard frost and store them in the basement or the fridge.