Answer: This can happen for several reasons. First, the bulbs must be large enough and strong enough to bloom. They build their strength through their foliage, so it must be allowed to grow, mature and ripen naturally in order to restore the bulb each year. They should be planted in full sun and in soil that is of at least average fertility. You might give them a top dressing of compost and/or complete fertilizer in early spring as they begin to show, in mid spring after they bloom and again in early fall when they will be beginning to grow again. This should help them gain some size adn strength from year to year.
Next, large bulbs tend to divide into smaller bulbs and these smaller bulbs may take a few years to reach blooming size. If you planted top size bulbs, they may have divided quickly. Next, tulips that are planted very shallow tend to divide more often than those planted at a deeper level.
Finally, some tulips simply perform better over time in the garden than others.
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