By Rina Peck, Colorado State University Cooperative Extension Master Gardener, Denver County
Growing perennial flowers in mountain gardens is no small feat. Only the tough prevail at high elevations.
Many Colorado mountain gardeners must accept a 90-day growing season with the last killing spring frost a month later and first average fall frost a month earlier than Front Range gardeners, who enjoy the luxury of a 150-day growing season.
Plants for mountain areas must be able to withstand daily temperature fluctuations of forty degrees, high summer heat, intense sunlight and cool nights. Water is one of the most limiting factors. For many mountain homeowners with wells, watering plants in July can mean a choice between the flowers and a post-gardening shower.
Location, planting and care are of equal importance to plant selection in mountain perennial growing success.
Location differences are magnified at high elevations. Pronounced microclimate effects from the interplay of sunshine, objects and terrain make plant location decisions critical. A plant growing in the shade of a rock may as well be in a whole different climate than the same plant located 3 feet away in full sun.
Take advantage of cooler eastern exposures to reduce evaporation or the drip line of a roof to harvest water. If your growing season is especially short, consider planting in barrels on wheels or in portable containers. Move the containers to follow the path of the sun across the sky over the seasons. Take advantage of sheltering walls and overhangs in cooler periods and sunny open spaces during warmer times.
Plant in late spring to early summer, June to July. Take time to amend soil with compost, peat or well-composted manure. This helps shallow, rocky soils hold the balance of water and air needed for root growth.
Check newly planted plants every few days for the first several weeks and water when the soil is dry. Avoid frequent sprinkling by applying ample quantities of water that encourage deep rooting. After one growing season for root establishment, plants will thrive on periodic deep watering.
These less-thirsty perennials grow well in my garden located in a chilly valley at 8,000 feet elevation. Many can be seen growing in gardens as high as 10,000 feet.
Look for the compact varieties of catnip (Nepeta) for lavender, bugle-like flowers to edge the garden. A ground-hugging companion is Mount Atlas daisy (Anacyclus depressus). Its red buds open to reveal delicate white petals on sunny days.
Thrift (Armeria maritima) is another edging plant that forms evergreen cushions with pink globe blooms. Include silver-green snow-in-summer (Cerastium tomentosum) for a mass of white flowers early in the season. Shear this plant after bloom and you may be rewarded with a second show of white flowers.
Among taller, "water-wise" perennials, Oriental poppy (Papaver orientale) provides a dramatic, orange spring display. Both dwarf and 2-3 feet tall yarrow are desirable for the golden flat-topped blooms.
Yarrow makes excellent fresh and dried cut flowers and adds garden color through the summer.
Mauve-flowered beebalm (Monarda fistulosa) grows on dry hillsides and does well when planted among other tall flowers to conceal the spindly stems. Consider support from baby's breath (Gypsophila paniculata) and tall native daisies (Erigeron sp.).
Drought-tolerant mainstays for mountain gardens include the deep-blue starburst flowers of mountain blue (Centaurea montana) and orange-yellow blanket flower (Gallardia aristata). Consider pairing both with oregano (Origanum) for its light green leaves and gently-waving, purple flower spikes. These combinations are irresistible to painted lady butterflies, as well as to a host of other insects such as bees and fuzzy bottlebrush flies.
For a partially shady spot, try bellflowers (Campanula sp.). Plant habits range from low-growing clusters to tall, nodding show plants.
Perennials are a sure-fire way to jump start the high elevation gardening season. The rugged corduroy leaves of catnip and prickly growth of Oriental poppies are welcome signs of spring in the high country.
For more information see CSU Fact Sheet 7.406, "Garden flowers for mountain communities."
Photograph courtesy of Judy Sedbrook.
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010