Welcome to GoY Ken..Most people cut off the flowerheads,when they are finished,and leave the rest of the plants to die down naturally,or when the foliage has gone yellow..it's beneficial to give them a feed at that stage,to build up the bulbs for next year..

Feed before the leaves go yellow with half strength tomato food and, as Bloomer says, let the leaves die back naturally.

Don't be tempted to bend them over and tie them though as that prevents the goodness from getting down to the bulb.

Good advice given above.