Answer: If bulbs are overcrowded and have to compete for moisture and nutrients, they sometimes do not flower. If you cut off the green foliage instead of allowing it to turn brown on its own, it can prevent flowering, as well. And, especially with tulips, some varieties perennialize better than others. Some bloom for a year or two and then peter out. If your are three or more years old, they may have already given their best display and will decline from now on. You have a few months to decide whether or not to replace them. This fall there will be lots of healthy new bulbs in the garden centers. I hope this helps you trouble shoot.
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