Easy Alpines for Colorado Gardeners
By Mike Kintgen:
As summers get hotter and hotter, alpines may not be on most gardeners’ radar, yet here are five easily grown, Colorado native alpines to try in your garden or trough.
1. Erigeron compositus, the Cutleaf Daisy, tops my list for all rock gardens or troughs. Found over a massive part of Western North America, from steppe to alpine, it has a wide variety of forms and colors. White, pink, lavender, and almost pale blue are all in cultivation. Sizes vary from 2" tall Red Desert and Railroad Ridge to forms that are 6-8" tall. Hailing from such a wide variety of habitats, cutleaf daisies tolerate a wide variety of conditions. The alpine forms are best in a trough or crevice garden that is not baked. The montane and steppe forms can take a bit more heat and drought, but are still best with a reprieve from hot afternoon sun.
2. Aquilegia saximontana, the Rocky Mountain Blue Columbine, is endemic to Colorado, meaning it’s only found within our state boundaries, mainly on the Front Range from Pikes Peak to Rocky Mountain National Park. Being so rare in the wild one would think it would be difficult to grow. In a partially shady trough, crevice garden or well drained site it has been easy and long-lived for a columbine.
3. Telesonix jamesii, James Saxifraga, is largely endemic to Colorado, with a few populations in New Mexico. Bright pink flowers grace this crevice and shade lover in spring. My longest-lived plants have been in a trough but they also like crevice gardens. All it asks for is some shade and regular moisture.
4. Eriogonum umbellatum var porteri, Porter's Sulphur Flower, has an alpine form scattered across some of the highest peaks of the Western US. Despite its lofty origin this bright yellow sulphur flower has settled down nicely in two hot and dry locations at Denver Botanic Gardens (DBG). The flowers are more golden than Plant Select's ‘Kannah Creek’ or another Montane/foothill version of E. umbellatum. Give it sun, well-drained soil, and an occasional drink in the hottest, driest spells.
5. Peterophytum caespitosu, Rock Mat, has also stood the test of time in the Rock Alpine Garden at DBG. Native to cliffs and boulders throughout Western North America, it excels in troughs and crevice gardens. My original plant started from seed in 2005 still graces a trough at DBG. Rock Mat is actually a dwarf shrub with wood stems under the blue-green leaves and spikes of white flowers in mid to late summer. Ancient mats on sandstone and limestone cliffs can be a meter wide, but my 18-year-old specimen is about 6-8 inches across. It's not a plant for instant gratification, but instead gets better and better with age.
Finding these gems can be tough now as our two best alpine nurseries have closed. Still, you may be able to find many if not all at The Rocky Mtn. Chapter of the North American Rock Garden Society sale in April (watch social media for dates in 2024) and at the DBG Spring Plant Sale just before Mother’s Day.
The North American Rock Garden society (www.nargs.org) offers a seed exchange to members each winter and many of these species are on the list, including multiple forms of Erigeron compositus. Growing plants from seed is time consuming but a fulfilling way to obtain plants.
Many alpines can be grown along the Front Range below 6,000' by taking microclimates into consideration. Alpines love afternoon shade or bright but dappled shade all day. Good air circulation is important; they despise hot, stagnant air. Troughs and crevice gardens (they need not be large) offer the best situation to grow and show off these gems. A small crevice garden built with some elevation (at least 24" high) to give drainage and a deep root run, preferably facing east or north to stay cooler, are great. My most successful troughs have been in bright but somewhat shaded areas. Morning sun and bright shade the rest of the day are perfect.
Mike Kintgen is the Curator of Alpine Collections at Denver Botanic Gardens. He holds an MS in Environmental Biology and a BS in Landscape Horticulture, and gardens in Denver and Routt County, CO.