My favorites are the single and double early classifications (both have short stems) followed by Triumph tulips. Fosteriana and Greigii also work.
Most other divisions that naturally bloom in mid to late season usually aren't suitable to force; in particular Vividiflora, Fringed, Lily Flowering, most Parrots, Double Late, and Single Late. Darwins can be forced but their height is a drawback. I've only had limited success with the species.
Tulip bulbs have a rounded side and a flat side; when placed in pots, the flat side should face the outside of the pot. This allows the tulip to unfurl it's first leaf toward the perimeter of the pot and results in a fuller 'look'.
