The act of setting seed can use up as much as 30 percent of the energy of tulips in spring. That’s why it’s smart to dead head tulips, encouraging subsequent bloom while providing a tidier look. Daffodils, on the other hand, reproduce differently from tulips. There is no need to dead head them after bloom. In order to regenerate for new growth next spring through photosynthesis, the foliage of all spring bulbs must be left in place to die back for a minimum of six weeks after bloom. After this period, the withered leaves may be cut back to ground level.

 Why dig them up? 

In Holland tulip growers dig up their bulbs every year to ensure high quality blooms and get new bulbs for the coming fall.  After digging they divide the bulbs (A bulb multiplies into 1 big bulb and several baby bulbs). The big bulb they sell and the small baby bulbs they plant again next fall (to grow big bulbs again...) this is how they multiply their tulips. In your own garden you can do the same. Multiplying will even go faster because you will not sell any of your bulbs... That they are multiplying sounds nice, but the problem is that tulips don't grow well if it gets crowded which is why it is important to dig them up and separate them.