Longwood Gardens’ Grows Largest Mum Outside of Asia | Longwood Gardens. NOVEMBER 3, 2015, Kennett Square PA – Longwood Gardens has unveiled the largest chrysanthemum ever grown outside of Asia: the Thousand Bloom Chrysanthemum. The amazing plant features 1,509 perfectly placed, uniform blooms on ONE plant. The Thousand Bloom Mum is a highlight of the annual Chrysanthemum Festival at Longwood Gardens, which transforms Longwood’s 4-acre conservatory into a vibrant visual feast of colorful chry...