How often you have to dig up tulips depends on the variety and your climate. Some tulips only bloom reliably for one year, regardless of climate. A few of the larger tulip varieties can flower each year, but only when grown in climates that provide for their winter dormancy needs. You can still grow these tulips in milder climates, but they require annual digging. Small tulip varieties, including Tulipa clusiana and Tulipa bakeri, don't require dormancy and can bloom reliably with minimal digging in milder USDA zones 8 through 10.
Can you leave tulips in the ground all year? It depends. Most tulips, except for some small varieties, require a cold dormancy period to bloom in spring, which they can't receive naturally in mild regions where temperatures rarely drop below 45 degrees Fahrenheit.
The cold dormancy period must last for eight to 10 weeks or the bulbs won't send up new growth. In mild or warm climates, you must dig up the bulbs in fall, store them in a refrigerator for three months, and replant them in late winter if you want them to bloom again.
Perennial tulips that remain in the ground, including small varieties in mild climates and large types in colder regions, will require periodic digging and division. Tulips produce offsets, or new bulbs, off the old bulbs. Eventually, the old bulbs stop producing and the new bulbs take their place. Over time, too many new bulbs cause a crowded bed and the tulips flower poorly.
The bulbs need to be dug up and divided about every three years, or when they stop flowering well. Dig them up in early summer or in fall before frost. Break apart the new bulbs, discard the old, and replant the remaining bulbs at the proper spacing.