How long would it take to dye white roses blue through sticking the roses in blue food coloring?

You should see some color within a hour or two, but usually overnight and sometimes into the next day. You may have to recut the bottoms every 12 hours to encourage uptake, also try to keep the stems in the water when you cut them so air bubbles don't get into the stem. Keep the foliage on the stems as they will help pull the water up. If the rose is old, fully opened, no, there won't be much uptake.

How long would it take to dye white roses blue through sticking the roses in blue food coloring?
Umm...Why don't you just get a genictically altered rosebush instead. Burpees has one called Blue Ribbon that gets it's blue from Bluebells or Iris.
Reply:You cut the stem %26amp; put them directly in blue tinted water.
Reply:Overnight. They won't turn completely blue.