Trelissick Garden is one of the best garden outings near Truro, set above the Fal estuary with woodland walks, lawns, and planting that benefits from Cornwall's mild climate. The water views give the estate a broader sense of place than a simple walled garden.
It works well as a half-day from Truro, especially if you combine the garden with ferry routes or countryside driving. Check seasonal colour and National Trust opening details before going.