Opposite words for blossom:
downfall, decay, withering, nadir, wilting, bottom, shriveling, decline.
Usage samples:
  1. Seeds from those having small blossom- marks, bear very few, and from those having large ones, produce abundantly.
    "Soil Culture", J. H. Walden.
  2. Here's a big blossom you haven't tasted!
    "The Tale of Freddie Firefly", Arthur Scott Bailey.
  3. " But beauty is better than all this," still said the proud little apple blossom.
    "A Child's Story Garden", Compiled by Elizabeth Heber.
  4. When working, the male would fly back and forth from the ground to the nest, carrying his bits of plant stem, oak blossom, and other fine stuff.
    "A-Birding on a Bronco", Florence A. Merriam.