This is what happens immediately after the Rose Parade and I think you can see the floats for several days

After every Rose Parade, the floral masterpieces are parked along Sierra Madre and Washington Boulevards in Pasadena and exhibited for visitors to walk by and see in close detail the design and workmanship that goes into these floats. Visitors are able to walk within a few feet of the floats and appreciate for themselves the creativity and the imagination of the floral displays. The Rose Parade floats have been a Pasadena tradition for over 100 years. Of course, White Suiters will be on hand to answer your many questions. Please come and enjoy the beauty and imagination of these floral creations.

I can ask some peeps I know involved in the parade what happens to all the flowers after but I imagaine there is some sort of green recycling effort.