Plains Plateaux and Peaks

• Mesic Rock Garden Plants
• Mesic Bulbs
• Xeric Rock Garden Plants
• Xeric Bulbs
• 25 More Challenging Plants for the Advanced Rock Gardener
• Bulbs

Mesic Rock Garden Plants

    We are fortunate in the Rockies to have a rich palette of rock garden plants to utilize in our gardens: however, the nature of the steppe climate where most cities are cited in this region presents challenges for rock gardeners. Drought—or more simply put—dry spells can occur most any month, and they can extend for weeks and months on end. The classic high alpine plants of Europe or our Pacific Northwest cannot tolerate the heat and prolonged drought. They are best sited in shady microclimates, and most must not be allowed to dry out. I find watering several times a week is necessary to maintain primroses or androsaces in Denver during the summer months. Gardeners at higher elevations will have to do even more. (First figure is height by width at maturity.)

Achillea ageratifolia

3" x 12" White daisy flowers in May-June. Silvery, hairy mats of almost succulent foliage year around.

Androsace sarmentosa

3" x 10" Bright rose nosegays in May, strawberry runners end in silver pompoms making substantial mats when happy: gorgeous!

Aquilegia saximontana

5" x 7" Irresistible, tiny flowers with hooked spurs produced over long season over delicate foliage. Some shade is best.

Arenaria tetraquetra

1" x 10" Very dense, steely cushions with neatly cruciform rosettes with white spring stars. Easy in sunny scree or crevices.

Artemisia assoana

3" x 8" Congested mounds of filigree foliage for sun: tiniest sagebrush.

Campanula garganica

3" x 12" Attractive mounds of bright green leaves ringed with lavender stars in late spring and summer. Essential!

Delosperma basuticum

1" x 8" Tufted ice plant with white-eyed yellow blossoms in spring.

Dianthus anatolicus (D. simulans Hort.)

2" x 12" The most compact cushion of pinks, spangled with tiny pink flowers.

Draba hispanica

3" x 6" Spiny, bristly rosettes form dense cushions. Early spring flowers in pungent yellow.

Edraianthus tenuifolius

3" x 8" Grassy tufts ringed with up-facing chalices of lavender or purple in late spring.

Erigeron compositus ‘Red Desert’

2" x 8" Densest, most congested form of abundant and tough Western cutleaf daisy. Superb in troughs. Blooms all summer.

Gentiana acaulis

3" x 8" Glorious cobalt blue trumpets in April and May over lustrous blue-green rosettes of foliage. A gem.

Geranium dalmaticum

5" x 15" Apple green mounds of attractive foliage turn vivid orange and red in late fall. Spectacular soft pink flowers over a long season in early summer.

Globularia cordifolia

3" x 12" Steely blue mats of rounded, evergreen foliage with blue pompom flowers in spring.

Heuchera pulchella

5" x 8" Lustrous evergreen foliage and nodding spires with pink, cup-like blooms.

Hypericum olympicum

5" x 15" Huge brassy yellow flowers with explosive boss of stamens open in May and June. Trim mounds of silvery leaves.

Jovibarba heuffellii

3" x 6" Attractive, thick rosettes flushed with red, with spires of yellow flowers in early summer. Choice hen and chick.

Linum capitatum

6" x 8" Gorgeous bright yellow stars of bloom in early summer on evergreen mounds of blue-green rosettes.

Origanum libanoticum

10" x 12" Cascades of shrimp-like flowers much of the summer and wonderful mounds of fragrant foliage. Very decorative.

Penstemon fruticosus

5" x 12" Lustrous, nearly succulent mounds of evergreen foliage forms a stalwart shrub on scree. Lavender trumpet flowers in late spring.

Pulsatilla halleri

6" x 8" Silky chalices of lavender April bloom with tousled seedheads in early summer. Shimmering foliage: choice.

Satureja montana ssp. Illyrica

3" x 10" dense mats of dark, blue-green foliage obscured by bright purple blue flower in late summer. Fragrant to boot!

Saxifraga paniculata ‘Millstream’

6" x 12" Deep red stars on delicate wands over silvery, lace-like encrusted rosettes. Superb among rocks in part shade.

Sempervivum ciliosum

3" x 8" Wonderfully eyelashed, silvery rosettes with short stems crowned by gorgeous soft yellow stars. Great!

Teucrium pyrenaicum

2" x 14" Woolly mats of attractive, scalloped rounded evergreen leaves spangled for months with rings of lavender and white blossoms.

Mesic Bulbs

Corydalis solida ‘George Baker’

3" x 12" Filigree foliage crowned with crimson red fumewort flowers in March and April. Needs some shade to do best.

Crocus speciosus

3" x 4" Huge, luminous lavender goblets in fall.

Iris suaveolens

3" x 6" Tiny mats of sickle-shaped leaves with yellow or purple flowers on very low stems.

Muscari (Hyacinthella) azureum

3" x 12" Tiny, sky blue hyacinths in March. Self slow liberally (and always welcome). Disappear in summer and never in the way.

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Xeric Rock Garden Plants

These are sun-loving, heat tolerant plants that thrive in Colorado with minimal supplemental irrigation. They do best on mineral soils (i.e., not heavily amended). They do not tolerate rich soils and frequent irrigation.

Acantholimon hohenakeri

12" x 20" Blue-gray prickly buns and purplish pink flowers on 10 inch spikes. One of the most attractive and widely grown.

Aethionema grandiflorum

10” x 15” What I have grown as A. grandiflorum tends to be slightly more diffuse and a darker pink than A. pulchellum —the other more commonly grown of the larger species. Both form twiggy, subshrubby mounds of blue-gray, evergreen foliage attractive in its own right. Both bloom for weeks on end in late spring, and thrive in the poorest soils. They may bloom spectacularly one or two years on richer soils, but live and bloom longest on harsher exposures and poorer substrates.

Alyssum montanum and A. wulfenianum

Both of these produce compact mats of silvery leaves 2" or so tall spreading up to a foot in time. They start to bloom in early spring, with fresh flowers emerging as long as cool nights persist into the summer months. With diligent deadheading and richer soils these bloom into the autumn months—outstanding edging plants for borders or for rock gardens and xeriscapes.

Aster coloradoensis

2” x 5” a tufted miniature that starts to bloom in May, with repeated flushes of bright pink blossoms all the way to frost. Dusty gray foliage is very attractive. Good for scree, trough, or choice crevice in the rock garden. Clear pink daisies bloom all summer amidst blue-green, toothed, curved leaves to 3 inches. This gem should be in every rock garden.

Astragalus angustifolius

3” x 15” high altitude cushion plant from the eastern Mediterranean appears to have persisted in cultivation over much of the past century—a dense, spiny dome-shaped subshrub with white pea flowers in late spring. Unlike most of the genus, it roots easily from cuttings or grows quickly from seed.

Clematis scottii

6” x 18”, a sprawling, glaucous cousin to C. hirsutissima from steppe habitats in the Southern Rockies . The lavender bell-shaped blooms are more rounded and it has a stronger tendency to rebloom in cultivation. Gorgeous golden seedheads.

Echinocereus fendleri

7” x 5”. This hedgehog type cactus produces a few deep green-stemmed clumps with few, heavy spines and very showy purple-magenta flowers in spring. Showy red spherical seedpods: easily grown and long-lived.

Eriogonum umbellatum var. aureum ex 'Kannah Creek'

12” x 24” Prostrate mats of leaves, dark green above, white hairy below, with good maroon fall color. This is the most widely available and adaptable form of this universal and extremely variable (and beautiful) native buckwheat.

Escobaria vivipara

4” x 9” The last ball cactus to bloom in the Rockies—often as late as 4th of July. Deep purple vase-shaped blossoms on the top of round, beautifully spined bodies that clump up to amazing size in this Great Plains race. Up to 50 heads in some clumps: a fabulous and very hardy native cactus easy to grow from seed. Dozens of variants with differently shaped stems and colored spines. Long-lived.

Gazania linearis

3” x 8” An abundant alpine gazania grows throughout the higher mountains of southeastern Africa where it blooms from spring to fall with brassy yellow flowers over dark, evergreen leaves. It is soundly perennial in Denver, where the flowers even open in the winter months in protected sites.

Helianthemum nummularium

6” x 12” Deep green or silver leaves with an immense range of flower color, very tolerant of a wide range of soils and conditions, easy and long-lived. Shear after spring bloom for rebloom. Do not cut back hard in fall.

Helichrysum plicatum

8” x 15” Woolly, evergreen mats like a curry scented Achillea, with refulgent yellow everlasting flowers in summer.

Heterotheca jonesii

2” x 15”. Surely the most stunning goldenaster—this densely pulvinate Utah wildflower blooms non-stop from spring to fall. For xeriscape or even troughs—but drainage must be impeccable.

Hymenoxys scaposa

12” x 15” Larger than average Perky Sue flowers on a neat grassy cushion of gray green leaves. This Great Plains specialty has been the longest lived hymenoxys, blooming from late April to autumn frost. Essential!

Oenothera fremontii ‘Shimmer’

5” x 15” Glamorous cousin to the Missouri evening primrose, this variant from the southern Great Plains has narrow, linear leaves of a shimmering silver color and large soft yellow flowers produced for months on end. Very heat & drought tolerant.

Opuntia fragilis ‘Potato'

5” x 8” Irresistible mounding, spineless form of the fragile prickly pear from southern Utah . It has perfectly spherical pads that turn deep purple in sunny exposures. Luminous magenta flowers.

Orostachys spinosa

8” x 5” Universal rosulate succulent of east-central Asia: fascinating artichoke-like rosettes morph through the season. Here each leaf ends in a bristle, and the entire plant is a silvery color. Extremely cold-hardy, and very ornamental at all times of year.

Papaver rupifragum

18” x 6” Here the basal rosette is composed of substantial, gray-green oblong leaves covered with fine hairs. The flowers are produced on willowy stems, height depending on moisture and shade—4" tangerine cups rebloom through the summer months.

Pterocephalus depressus

2” x 15” Superb evergreen cutleaf Scabious from the Atlas Mountains makes dense mats sporting flesh colored flowers all summer. Very tough in the garden.

Ptilotrichum spinosum ‘Roseum’

8” x 16” A dense, shrubby evergreen shrublet from Spain and Morocco makes dense cushion-like mounds that are completely purple for several weeks in Spring.

Scutellaria suffrutescens

3" x 8" Dense mats of tiny, dark green leaves and scarlet flowers all summer. Wonderful native of Mexico — surprisingly hardy considering origin.

Sedum hybridum

3” x 10” Low glossy green foliage makes a slowly ramifying mat turning brilliant red in fall. Bright yellow May-June flowers are luminous. Very tough!

Thymus comosus

3” x 12” Prostrate evergreen film of leaves and large, fuzzy candles of lavender pink bloom in August and September. One of the showiest thymes, from the Balkans.

Townsendia hookeri

2” x 6” A particularly tiny, silvery mass of narrow leaves with stemless daisies appearing in March and early April. Very distinctive Great Plains native.

Zauschneria garrettii

3” x 12”+ generally well under a foot, this is the first to bloom and the hardiest of the genus.

Xeric Bulbs

Allium karataviense

6” x 10” Rising globes of pale metallic-mauve glow above broad, pleated, glaucous leaves. An outstanding Allium!

Tulipa humilis

6” x 8” Widespread and variable rose or pink-colored tulip from Western Asia that naturalizes in dry gardens. Incredibly showy March–April bloom.

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25 More Challenging Plants for the Advanced Rock Gardener

You will encounter many classic rock garden plants at many garden centers in the Rockies: Pulsatilla vulgaris, various primroses, quite a few tiny campanulas, even androsaces and saxifrages are sold by many nurseries in our region. Many of these "common" alpines are common because they are easy to grow by nurserymen, and gardeners expect to find them. After you have gained confidence with these there is a whole other level of plants needing a bit more care and attention: many of these are increasingly commonly sold at the better garden centers in our region. This list includes a few of these "choice" alpines that are less frequently encountered, but worth every effort to tame.

Aloinopsis spathulata

2" x 5" Gnarly succulent from S Africa with gray, elephantine leaves and heavenly pink cactus-like flowers in April. Hardy to zone 5 in well-drained scree.

Amsonia tharpii

12" x 5" Graceful white-flowered vase shaped miniature with waxy white trumpets in early summer.

Androsace x 'Millstream'

1" x 5" Congested cushion with stemless pink flowers in April-May. For a trough.

Astragalus utahensis

2" x 8" Silvery mats with sugar pink pea flowers in April and May, hairy bubble-like seedpods in early summer. Well-drained or xeric scree.

Bolax glebaria

1" x 15" Astroturf textured South American for moist scree with chartreuse flowers.

Campanula allionii

2" x 10" Huge stemless trumpet flowers over grim oval carpets of silvery leaves.

Campanula incurva

8" x 18" First year rosette with rounded leaves produces a summer-long shear of huge lavender or white cups. Monocarpic, but self sows moderately.

Cyclamen purpurascens

3" x 8" Hardiest and most fragrant cyclamen needs shade. Blooms much of the summer.

Daphne arbuscula

3" x 12" Dark green shrublet is extremely adaptable with heavenly, fragrant rose purple trumpets in spring.

Draba polytricha

1" x 5" Dense wooly cushions are surprisingly adaptable. Flowers begin in March and last to May. Best in troughs.

Dracocephalum botryoides

2" x 8" Shaggy, tight mats of scalloped leaves and soft lavender-purple flowers in early summer.

Eriogonum caespitosum

3" x 12" Tight silvery mounds of rounded foliage topped with bright yellow or orange flowers in early summer.

Gypsophila aretioides

1" x 8" Dense, rock-hard cushion produces minuscule flowers if you are careful to look. The ultimate cushion plant! Best in troughs or crevices.

Hirpicium armerioides

2" x 10" Silvery cushions with white gazania-like flowers with dark reverses from April to frost.

Lilium philadelphicum v. andinum

15" x 4" Best NOT treated as a bulb, but purchased from nurseries in pots. Huge orange chalice is gorgeous in part shade with moisture.

Maihuenia poeppigii

2" x 12" Primitive cactus from the Southern Andes with tubular foliage among the spines on dense mats with gorgeous pale yellow flowers.

Matthiola montana

2" x 8" Fragrant crucifer with lavender flowers over hairy, attractive rosettes.

Othonna capensis

3" x 10" Succulent daisy from South Africa with gray lozenge-like leaves and endless succession of soft yellow daisies. Drainage and some moisture needed.

Pelargonium endlicherianum

15" x 8" Hot magenta butterfly blossoms over trim rosettes all summer long. Needs good drainage.

Primula ellisiae (rusbyi)

7" x 6" Heavenly pink primrose from the Southwest needing typical shady crevices. Reliable in troughs as well.

Salvia caespitosa

2" x 10" Dense silvery, pinnate mounds of foliage smothered with giant, face-like silvery white flowers in spring.

Telesonix jamesii

4" x 7" Raspberry-pink flowers in late spring over scalloped foliage that turns lovely tints in fall. Easy in troughs.

Teucrium aroanium

2" x 8" Spidery, lavender flowers are very attractive in spring over the spreading mat of oval, silvery leaves.

Thalictrum ichangensis

7" x 8" Peltate, rounded leaves and lavender flowers over this miniature for shade.

Veronica bombycina v. bolgardagensis

1" x 8" Most powdery-white veronica from southern Turkey with bright sapphire flowers.

Bulbs

Crocus sieberi

3" x 4" Usually found in a bright purple mode, this variable species is vigorous in cultivation, and thrives on neglect.

Iris bucharica

10" x 12" Pure yellow or yellow and white flowers tucked in the leaf axles of this ‘Corn iris’ are the easiest of the Junos to grow in this region: sun and drainage is all.

Narcissus asturiensis

3" x 4" Tiniest daffodil blooms in late March, thrives in buffalo grass lawns and naturalizes.

Tulipa sprengeri

15" x 8" Chinese sealing wax-red flowers in late May or June: the last hurrah for the garden tulips (and for items on this list as well...).

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