I believe it is the winter chill that they need to bloom. You would probably get them to bloom the first time by buying precooled blubs (or doing it yourself in a refrigerator). But the next year they probably won't bloom. Some species tulips grow in zone 10 but they do not have the same look as regular tulips. Think of everything you CAN grow!

Tulips will bloom beautifully in San Francisco. You should consider them as annuals, however as you don't have enough winter chill to bloom the second year. I always buy mine as soon as available, about the end of August and put them in my garden refrigerator until the first of December when they are planted in the garden. Dependable blooming is never a problem. When the bloom is over, just dig them up and compost or throw away. With the low cost of tulips, this is not a sacrifice. Al

Thank you both.

I have recurring tulips now so I thought it was strange to hear they 'might' not bloom.

I never realized some tulips need that cooling. I guess that explains why I get some to grow only once - I had thought it was because they got waterlogged over the winter and rotted.

Digging them up and refrigerating them is no problem so that's my regimen from now on.

Thanks again.