In the Northwest area (Oregon, Montana, Washington, Wyoming and Idaho), gardeners face an issue with bitter cold weather. The northwest United States is classified as USDA hardiness zones of 3a to 9b, depending on the area. (Check the USDA hardiness map for your location.) For garden plant ideas in this range, you'll want plants with a hardiness of 3 to 4. Zone 3 is hardy from -40 to -30 degrees F, and Zone 4 is hardy from -30 to -20 degrees F.
Peegee Hydrangea, or Hydrangea paniculata, is from the Hydrangeaceae, or hydrangea, family. It is a fast-growing shrub or tree with white to pink flowers---and can reach 10 to 25 feet with leaves 3 to 6 inches long. Flowers are on panicles (clusters at the end of stalks) 3 to 10 inches high. This plant prefers full sun or partial shade with moderate watering and is propagated via greenwood tip cuttings during the spring or summer seasons.
Purple coneflower, or Echinacea purpurea, is from the Asteraceae/Compositae, or aster/daisy, family and is a fast-growing perennial good for beginner gardeners and for attracting butterflies. This plant will die in winter and sprout again in the spring. Purple coneflowers grow up to 3 feet tall; leaves are dark green, 3 to 8 inches long. Flowers are 3 inches wide and daisy-like in purple. Purple coneflower prefers full sun with a tolerance for partial sun, is drought tolerant and is propagated via root division or seeds.
Foxglove, or Digitalis purpurea, is from the Scrophulariaceae, or figwort, family. Also a perennial or annual, this plant grows 3 to 5 feet tall with 4-to-10 inch dark green or wool-white leaves and tubular flowers 2 inches long, in the purple, pink, white, yellow, or cream color hue. Foxglove requires partial shade and regular watering. Soils must be cool, acidic, moist and organic. Propagate via seed in late summer or fall. Foxglove may self sow with the perfect conditions.
Garden lily, or Lilium hybrids, is from the Liliaceae, or lily, family and is a fragrant perennial. There are 80 to 90 species of lilies and they range from 2 to 10 feet tall with narrow leaves and flowers in many different shapes in all colors but blue. Garden lilies prefer well-drained soil in full sun. Propagate via bulbs in the spring or fall or by seeds (can be many seasons before flowering if from seed).