Question
my hyacinth are in full bloom, i need to know how to cut them, but there is a second flower . should i cut the first one or not.

Answer
Hyacinths don't lend themselves to cut flower arrangements, but they're yours so you can do whatever you want.  Besides, some people break rules, others make rules.  You make this one.

Cut at the base as close to the bottom as you can.  A diagonal slice will aid in water absorption.

This will not affect the blooming of a second flower.

Hope you got fragrant Hyacinths.  Thanks for writing,

THE LONG ISLAND GARDENER