Several scenarios could explain your bulbs' lackluster performance, and understanding a few key facts about tulips will help you solve the mystery. Like all green plants, tulips use photosynthesis—a process that turns carbon dioxide and water into sugars and starches—to create the energy to live. Photosynthesis happens in the leaves, and in the case of tulips, the bulbs store the energy.
Cutting off a tulip's foliage after it blooms also cuts off its energy supply. "It's important to let the foliage yellow so the bulb gains energy for next year," says Linda Miranda, senior horticulturist at the Chicago Botanic Garden. If you removed the foliage too soon last spring, your tulips may have stored only enough energy to produce foliage this year.
The type of tulip you plant (hybrid or species) also determines if the bulb will flower for years or dwindle away after a season or two. In general, you need to plant the tall hybrid tulips every fall for a spring display, while smaller species-type tulips (also called botanical tulips) will come back for several years and may even naturalize (that is, produce new tulips) in your garden.
"Most hybrid tulips aren't reliable enough to treat as perennials," says Miranda. "They don't last from year to year." Even if you let the tulip's foliage yellow fully, the bulb will likely store only enough energy to send up foliage the next spring—though Fosteriana hybrids, often referred to as Emperor tulips, and the Darwin hybrids generally bloom for two or more years.
Dividing and fertilizing your older bulbs may help them bloom again. "The ideal time to divide bulbs is after they flower, but if you're not getting any flowers, you can do it any time in spring," says Miranda. Dig up a nonblooming older bulb; it should have smaller daughter bulbs around its base. If the original bulb is split or doesn't have daughter bulbs, discard it. Replant the largest of the daughter bulbs 6 to 8 inches deep in an area with good drainage, such as a rock garden or raised bed that doesn't receive much summer irrigation. When you replant the bulbs, fertilize them with a balanced organic fertilizer. In fall, mulch your bulb beds with 2 to 3 inches of leaf mold or compost to protect them from freezing and provide nutrients. The daughter bulbs should bloom in two years. In the meantime, look into planting a few more botanical tulips this fall. Miranda suggests Tulipa greigii 'Oratorio' and T. kaufmanniana 'Fashion'.