Ornaments in Animal Crossing: New Horizons are found by shaking the decorated cedar trees on your island during the Festive Season (December 15–January 6).

When ornaments appear

  • Ornaments only start appearing from December 15 to January 6 , matching your system date (or when you time-travel there).
  • Only cedar (pine) trees with Christmas lights on them can drop ornaments; plain green cedars outside this window will not.

Where to get them

  • Plant or keep plenty of cedar tree saplings (bought from Nook’s Cranny or Leif) so some will spawn as lit, festive trees in winter.
  • These decorated cedars appear around your island (often on upper levels if that’s where your cedars are planted), so bring a ladder if your trees are on cliffs.

How to make ornaments drop

  • Stand in front of a lit cedar tree and shake it repeatedly; it can drop red, blue, and gold ornaments as crafting materials.
  • Make sure there is open ground around the tree; if every nearby tile is blocked by items, paths, or bushes, new ornaments will not spawn.

Extra tips

  • Gold ornaments are rarer than red and blue, so expect to shake more trees or for longer to farm enough for all festive DIYs.
  • Ornaments are used for festive furniture and decorations (like the Big Festive Tree, Ornament Wreath, and other holiday items), so stock up before January 6.

TL;DR:
Play during December 15–January 6, plant cedar trees, wait for the ones with lights, then shake those lit cedars to farm red, blue, and gold ornaments used for festive DIY recipes.

Information gathered from public forums or data available on the internet and portrayed here.