Should I cancel or delete a planting that failed?

Cancel it: the planting stays as a record with the reason, so next winter you plan from what really happened instead of what you remember. When hail, a late frost or flea beetles take a planting, right-click it, choose Cancel planting and write why: it stays in your plan and no longer counts in your expected yields.

Restore planting brings a cancelled planting back. Delete planting removes the planting and its tasks for good: keep it for a planting you entered by mistake.

The steps are in Manage your plantings.