Nothing. Tulips do this. One year they're spectacular, the next there's no sign of them. They usually dont live longer than a few years. There are some species that come up reliably for a while, forget the name but someone will chime in here. For me Daffodils and crocus are more reliable.

Jen

Most tulips that I have planted are atleast 5 to 6 years old and not only continue to bloom but also have multiplied. Both my mom and grandmother told me tulips should last about 20 years and then they may stop blooming. I have found in my gardens that it helps alot if I get the ground pretty soft with mulch a little potting soil and fertilizer, preferably manure.

I have to agree with the last post. For best results add compost every year and you will not need any other fertilizer. For most of us we are not consistent and patient enough to really get our soil in shape that the soil food web will produce our plant nutrients. Al