How should I allow flower bulbs to naturalise?

You should let flower bulbs naturalise by not lifting them from the soil. After they bloom, the plants have to be given the chance to die back naturally so that they can store newly produced nutrients in their flower bulbs for flowering again next year. Many flower bulbs, however, are not suitable for naturalising purposes. This is why you should be sure to check the information on the packaging when you buy the flower bulbs to see they are suitable for naturalising. Naturally, you can always experiment with other kinds to see if they might be suitable for naturalising in your particular garden.