Southwestern Colorado covers USDA Hardiness Zones 4 through 6 with a small portion of zone 7 present at the extreme southwestern corner of the state. A complex geography of rugged mountains, deep canyons and high plateaus results in micro-climates that vary widely within short distances, hence the existence of four planting zones within a relatively small physical area. A wide assortment of plants hardy in all four zones meets the area's special challenges and assures appealing diversity in the garden.
Ajuga reptans,or bugleweed, is a useful foundation planting. It works well as filler in flower beds and as colorful, textural ground cover for shady areas in the southwestern Colorado landscape. Growing to a height of only 2 to 4 inches, Ajuga spreads vigorously via rooted runners and can become invasive. Spring blossoms may be blue, purple, pink or white depending on the cultivar. Showy flower spikes elevate Ajuga's profile to 10 inches during its bloom period. Evergreen to semi-evergreen, Ajuga's foliage may be light green, dark green, bronzed, purple or variegated according to variety. Crinkled leaves are erect and arise from a central crown. Ajuga is a perennial that grows well in partial sun to full shade. Though it prefers moist, well-drained soils and appreciates regular watering during dry summers, Ajuga is adaptable to harsh conditions such as poor soil and heat.
Aster alpinus, alpine aster, is a daisy-like flower that does best in cooler climates such as that of southwestern Colorado. Low-growing alpine aster is a fitting choice for rock gardens or edging around flower beds and walkways. Growing to a compact 12 inches in height and width, alpine aster produces yellow-centered blooms in vibrant shades of pink, blue or violet depending on the cultivar. Flowers appear from early spring to mid-summer. Alpine aster requires a location in full sun with well-drained soil. This hardy plant will tolerate drought and is useful wherever water is scarce. Removal of spent blooms encourages repeat flowering and keeps plants and beds looking neat.
An asset to any southwestern Colorado landscape is Kolkwitzia amabilis, commonly known as beautybush. Beautybush is a deciduous shrub that produces clusters of small, soft-pink flowers in late spring. Dark green leaves are 1 to 3 inches long and turn yellow or red in fall. Beautybush can grow 6 to 10 feet in height and spread 6 to 8 feet. As it grows, beautybush develops an arching, rounded form that can become leggy as it matures. Removing the oldest stems after flowering will help maintain the shrub's graceful, cascading shape. Beautybush grows in sun to light shade, and its drought tolerance is a boon to gardeners in dry areas.