I moved or deleted a planting by mistake. Can I undo it?

Yes, right after, so a slip of the mouse never costs you a planting. Click Undo in the message that appears, or press Ctrl+Z (Cmd+Z on a Mac). It brings back a planting you just moved, duplicated, cancelled or deleted.

For a planting you cancelled a while ago, Restore planting brings it back. A delete you did not undo is final: that is why cancelling is the safer choice when a crop fails.

The steps are in Manage your plantings.