The main feature of the festival is a 1,000-blossom chrysanthemum, which is many blossoms–not necessarily 1,000–symmetrically arranged and all growing from a single plant. Last year, as I recollect, it had 937, so this year I expected it to go over 1,000, and so it did, easily. I had assumed it was the same plant growing larger each year, but no, they begin training a new plant each spring. They all end up as compost when the festival ends.
You can see a video of how they do this at http://www.youtube.com/longwoodgardensinc#p/a/u/2/lXjqTFi5JVU or just go to their website, http://www.longwoodgardens.org and get to it from there.
My favorite, however, is a smaller chrysanthemum plant with dozens of grafts of different varieties, so you have one plant producing wildly different shapes and colors of chrysanthemum blossoms. This is not mentioned on their website, but look for it if you go. There will be many volunteer guides who can point it out.