Continue writing the next sentence.

How to force tulip bulbs in water
Trick the bulbs using a cold environment to make them flower.
Bulbs need to be' tricked' into believing they have survived winter in order to start flowering. This means they need to experience a sustained cold environment whilst they are dormant.
The ones you buy commercially are likely to have been chilled for you. If you are supplying your own bulbs, you'll need to recreate this cold environment yourself.