Why we dig our bulbs?
Tulips bulbs will multiply each year, if we left our bulbs in the ground we would have inferior tulips for you to pick next Year. They are also prone to disease, a disease could wipe out the whole field and crop insurance is not available for tulip growers. As a home owner you can leave your bulbs in the ground each year dig every 3-5 years to divide the baby bulbs from the mother bulb.
Its very important to leave the foliage to die back on your tulips after they bloom. The foliage will feed the bulb so that you will have beautiful blooms next year. We wait till the end of June to dig our bulbs. We currently use a potato digger, it is not perfect , but gets the job done.
The bulbs are sorted and separated and stored to be planted in the fall. Below is a picture of a bulb to show how they mature and multiple.