In their mile-high garden in Hailey, Idaho, not far from Sun Valley, Sally and Russ Horn prefer to plant flowering perennials in autumn.

Protected by the area's reliable snow cover from mid-December through mid-April, the plants emerge in spring strong enough to withstand the rigors posed by weather.

The Horns' cottage-style planting, pictured here in July, shimmers with white Shasta daisies; delphiniums in shades of pink, blue, and white; crimson-flowered clematis (at foot of birdhouse); yellow foxgloves; and purple veronica. Perennials thrive in this area where summer nights are cool and the days are warm but not hot.