daffodils

If you mean that the leaves have died back completely then you can trim them off. Either leave the bulb in the ground to grow again next year or lift, keep dry for the summer and replant in autumn. If it is just the flowers that have died off dead head and wait for the leaves to die back before removing.

If the leaves really are fully dead (and make sure they are) they will pull off easily with your hands. When the bulbs have finished with them they will cease to be significantly connected with them. Then its time for tidy up.