Bring flowers and water to a boil in a medium-sized pot on high heat.
Remove from the heat and cover. Cool to room temperature, then refrigerate overnight.
Use a fine sieve to remove the flowers.
Weigh the remaining redbud-flavored water and add an equal amount of sugar (by weight).
Bring the mixture to a boil and then reduce to a simmer, stirring periodically. Cook until desired thickness is reached. At about 25 minutes it will still be thin, but great for cocktails. Keep it going another ten minutes or so for a thicker syrup.
Reader Jacqueline shared this great tip: "My soaking water was a murky green. And the longer it boiled, the greener it got. It occurred to us that it might be a pH issue, so I added a little lemon juice and now my syrup is a lovely bright pink! Kitchen chemistry for the win!"