Northern Drylands

Aethionema grandiflorum

Persian Stonecress is a long-lived and undemanding plant for the sunny rock garden, and is native to Turkey, Armenia and northern Iran and Iraq. The four-petalled flowers, characteristic of the Brassicaceae family, are produced in June here and add a long-lasting touch of soft pink to the sunny garden. The elongated stems with their narrow but fleshy alternate leaves die back to woody stems here in winter but they may be evergreen in milder zones. The genus Aethionema contains many other easy-to-grow species, most of which flower in white and various shades of pink.

Androsace spp.

Several Androsace species are easy-to-please and very rewarding for the beginner and for the more experienced rock gardener alike! The species that propagate themselves by runners seem to be easier to obtain, and to grow, than the cushion species.
Androsace primuloides (which may also be referred to as Androsace studiosorum) is easy in a trough or sunny rock garden. It spreads modestly by runners, and blooms in late June-early July with bright purple-pink flowers.

Androsace chamaejasme is also surprisingly easy to grow. It blooms through May here, but much later in its native haunts on montane slopes and in rocky alpine areas in the neighboring Rockies. The flowers start out a pristine white with yellow centers, but as they are pollinated, a pink flush extends out from the center. Be sure to get close to appreciate the pleasant fragrance of the well-named "Rock Jasmine".

Arabis procurrens, Arabis xsturii

The white, four-petalled flowers on these plants are early, though modest to say the least – it is more the neat, mounding foliage that makes them worthy of attention. The ‘Variegata’ form of A. procurrens is especially attractive in spring and fall, when the white-edged foliage becomes flushed with pink. The foliage of A. x sturii is an unusual rich dark green. Both are evergreen, and add interest to the shoulder seasons, and also through the winter in low-snow areas.

Aster alpinus

Aster alpinus is an alpine garden stalwart that is native to the Alps and Pyrenees of Europe. It is long-lived and easy-to-grow in the sunny rock garden. The only attention it may need is some additional water in times of low rainfall. It flowers in shades of pink, purple and white.

Campanula spp.

The genus Campanula consists of about 300 species, found only in the northern hemisphere. A great number of the smaller species in this genus are classic rock garden subjects, and the good news for us northerners is that it is difficult indeed to find a Campanula that is not hardy to at least zone 3! From the many cultivars and hybrids of Campanula carpatica, to our native Campanula rotundifolia, to the exotic beauty of Campanula saxifraga, few genera provide a better flower show in the rock garden. Many do well even in regular garden soil in our dry conditions. (Do be careful to read up about, and avoid, the relatively few invasive species.)

Carlina acaulis

Those who appreciate the unconventional may want to seek out this well-behaved European alpine thistle. The spiky flower buds, in particular, are fascinating in their intricacy and the late bloom adds welcome interest through late summer and fall, and even through the winter.

Colchicum autumnale

These fall-blooming Crocus relatives are native to central and western Europe and the United Kingdom. The large bulbs of Colchicum autumnale and its hybrids and cultivars are sold in fall at garden centers, where they can sometimes be seen blooming from the naked bulb! The broad-leaved, vaguely hosta-like foliage emerges in spring and dies down by early summer…without flowering. Then, in late August through October, the large white or lavender flowers emerge – without foliage – for a spectacular end to the northern bloom season. The hybrid ‘Waterlily’ is a showy double-flowered form that is readily available. The plants are very long-lasting and the flower display increases from year to year.

Draba rigida

Overwintering as a dull grey mound, spring brings a rapid transformation to this easy alpine, as each tiny leaf rosette emerges and melds with its neighbors to form a hard, bright green cushion. Soon after, in May and June, the tight mound is smothered by short-stemmed racemes of brilliant yellow, four-petalled flowers. This species is native to Armenia and the Caucasus.

Geranium cinereum

Geranium cinereum and its many cultivars are easy, modestly-spreading perennial geraniums that are suitable for the rock garden, and tolerate sun to part shade in any soil.

Heterotheca jonesii

Despite that it is known only from a restricted range in SW Utah, Heterotheca jonesii is an undemanding rock garden subject in this area. It produces simple yellow daisy flowers generously through a very long season from June to killing frost, from a low-growing evergreen mat of narrow, hairy silvery leaves.

Jovibarba spp.

Jovibarba are the lesser-known cousins of Sempervivum and are distinguished from them by their bell-shaped, 6-petalled flowers. Another amazingly hardy succulent, the small rosettes of Jovibarba add interest in troughs and in rock crevices in the alpine garden.

Leontopodium alpinum

For a species that is somewhat emblematic of European alpine flora, Edelweiss is a surprisingly undemanding plant in cold, dry areas. Its felted leaves and bizarre silvery flowers can be enjoyed here so long as it is provided with reasonable drainage and some additional water during dry periods. (An odd bit of trivia is that public awareness of this species in North America comes not, seemingly, from the worlds of alpine gardening or travel but mainly from the song in the Rodgers and Hammerstein 1959 musical, "The Sound of Music"!) The species is native to a broad region that encompasses the mountains of Central Europe and into Asia.

Penstemon spp.

Penstemon is an almost-exclusively North American genus with about 270 species, the majority of which are well adapted to dry conditions. They range from woody shrubs to taller herbs to dwarf cushions, generally with neat foliage, and showy flowers that occur in the most amazing shades of blue through purple, to white and yellow, and even red. It is a mystery why they remain so underutilized in the garden!
    To see what the fuss is all about, why not try the following beautiful northern prairie Penstemon species in the rock garden?
Penstemon nitidus grows wild across the Canadian prairies and extends into SE B.C. and south to Washington, Wyoming, NE Colorado and North Dakota. It is a distinctive-looking plant, with bluish foliage and rounded leaves, but the real show comes with the bloom! The flowers are the most exquisite shades of sky blue though to indigo and purple. It is the earliest blooming of the native penstemons here, and will do well even in regular soil in our dry climate. Seeds can be direct sown where they are to grow, and they will benefit from "stratification" (exposure to fluctuating temperatures) over the winter. Grow this plant and it is guaranteed that you will be the envy of those in much warmer, but wetter, zones where it cannot be grown without great difficulty!
Penstemon procerus is a smaller-flowered cousin to P. nitidus, that forms compact clumps. It blooms in a similar colour range, and will extend the Penstemon bloom season in your garden. Its native range is from the southern Yukon and B. C., across the Canadian prairies from Alberta to SW Manitoba, and south to Colorado and California.
The third recommended native penstemon introduces a change in flower colour to creamy white. Penstemon confertus has many clusters of prominent flowers that are spaced out at intervals ("interrupted") along the stem. Its range is somewhat more restricted than that the foregoing species, occurring from SE B.C. and Alberta to Oregon and Montana.
    Penstemons are generally very hardy, requiring only good drainage and no excessive moisture, and so are ideal for the dry garden, and especially for the rock garden. It is hoped that a start with the native species noted above will provide an introduction to the very rewarding world of growing Penstemon.

Primula marginata

A long-lived and undemanding primrose that is native to the Alps of France and Italy, Primula marginata blooms in May. The various cultivars have flowers that range from bluish to pinkish and lilac, and the leaves are white-edged and jagged. Another classic alpine, this species has been in cultivation since 1777!

Pulsatilla vulgaris

The European "pasque flower" is extremely hardy and puts on a great display as it flowers through late April and May. The showy seedheads extend the interest far beyond the actual bloom, and the plant self-seeds moderately to add to the display. Pulsatilla vulgaris is native to Great Britain, through France to Sweden, and into the Ukraine. One's exploration of the genus Pulsatilla should not stop with P. vulgaris. There are numerous other, very attractive species that are just as easy to grow, though these are often less readily-available and may have to be grown from seed.

Rhodiola rosea

This interesting and very hardy Crassulaceae has a very broad circumboreal distribution, ranging through central Asia and the mountains of Europe, across Scandinavia, Iceland, Great Britain, and Ireland, and through eastern North American and the eastern Arctic. It is small enough for the larger trough and blooms through May and June.

Saxifraga sancta var. macedonica

As this Kabschia saxifrage is extremely hardy, undemanding, and reasonably available, it is a good choice for the beginner, and can provide the springboard to trying the many other saxifrage species, hybrids and cultivars that perform well in this area.

Sempervivum spp. and cultivars

"Hens and chicks" are so well known that it is easy to forget that these carefree succulents are true alpines from mountainous regions in Spain through to Austria. Many species and cultivars are amazingly hardy and are easy to grow in full sun in any well-drained soil, but it should be noted that they are especially attractive when grown in rock crevices in the rock garden or in troughs. The species and cultivars with smaller rosettes are particularly well suited to the alpine garden.

Thymus praecox 'Minus', 'Elfin'

While many thymes are too tall or too vigorous for any but the largest rock gardens, the tiny-leaved forms of T. praecox are ideal for planting in the crevices between flagstones.

Veronica spp.

A wide variety of Veronica species are very hardy, easy to grow, and well-suited to the rock garden here.
    Veronica whitleyi is a particularly floriferous, mat-forming species that blooms from earliest spring to latest fall.

Vitaliana primuliflora

This is a choice but surprisingly-easy alpine from the mountains of Europe. The foliage consists of spiky rosettes that form an evergreen mat or low mound that is covered in bright yellow, stemless flowers through May.