In battle
If the Pokémon has used a Berry, there is a 50% chance of it being restored at the end of each turn. The held Berry is remembered even if it is not restored or if the Pokémon has switched out. Harvest will always activate in intense sunlight.
Harvest can recover Berries consumed by Fling and Natural Gift, but not Berries transferred to another Pokémon, Berries destroyed by Incinerate, Berries knocked off with Knock Off, or Berries eaten with Bug Bite or Pluck. Harvest cannot restore a Berry if it is collected by a Pokémon with Pickup.
A single Pokémon's Harvest will not activate more than once per turn. If the held Berry is consumed immediately after it is restored, Harvest will not be able to restore it again until the next turn.
Harvest can recover Berries consumed that were originally another Pokémon's, but transferred to the Pokémon with Harvest. However, a Pokémon may only have one consumed item (including non-Berries) at a time; if a Pokémon consumes a Berry, obtains another item and consumes it, the original consumed Berry cannot be restored, even if the second item is restored and swapped away. If the Pokémon with Harvest obtains an item after consuming a Berry, Harvest can still restore the old Berry as long as the Pokémon has no hold item and did not consume any other items (including non-Berries) since consuming the old Berry.
Outside of battle
Harvest has no effect outside of battle.