“One of the very best things about the rock garden is that there is a seemingly endless list of plants to learn and grow. That sheer diversity means rock gardening never gets old or tired or familiar; it is forever fresh and exciting no matter how long you’ve been tucking plants between stones.” 

— Joseph Tychonievich, “Rock Gardening: Reimagining a Classic Style,” 2016

“Rock Gardening” author Joseph Tychonievich is right about the dizzying array of plant choices that are available for rock gardens, especially when you go beyond the classic style that utilizes true alpine plants. In fact, I’m learning that today’s rock gardeners make use of plants that fall into three general groups: alpine plants, xeriscape plants and woodland plants for shady sites.

Classic alpine plants are those that evolved in the harsh conditions of high mountain regions. Growing above the tree line, these plants are exposed to harsh winds, limited water, and intense sunlight. They have adapted to these conditions by staying small and compact and forming tight mounds or spreading mats of foliage. There aren’t many pollinators at such high altitudes, so alpine plants often produce brilliantly colored and/or disproportionately large flowers to compensate.

The benefits of using alpine plants in a rock garden are many: they are beautiful and diverse; they’re able to withstand harsh, erratic weather; they develop deep roots to find moisture during times of drought; and they thrive in rocky or gravelly “poor” soils that don’t require fertilizers. In fact, once happily established in a garden, alpine plants are virtually fuss-free.

The downside of using alpine plants in a rock garden is that bloom time for individual plants is usually quite short – often only a few days. Alpine plants need good water drainage, so they won’t grow well in soils with a lot of clay that retain moisture. Depending on the mountains they originated from, alpine plants may need alkaline soil, whereas a lot of the soils in our area are on the acidic side.

In addition, alpine plants have adapted to cold winters and might not fare well as our winters become increasingly warmer. During warm, wet springs, alpine plants are particularly vulnerable to fungal pathogens that can cause crown or root rots. Excess water can cause alpine plants to develop loose, open foliage that spoils their aesthetic effect.

Despite the challenges, many local rock gardeners grow alpine plants successfully. Here is a listing of some commonly used alpine plant species and cultivars, some of which are North American natives.

Campanulas: C. portenschlagiana, C. cochlearifolia, C. carpatica.

Cyclamens (one of the few alpine plants that grow in shady gardens): C. hederifolium, C. coum, C. purpurascens.

Daphnes: D. alpina, D. petraea, D. x napolitana ‘Stasek’, D. jasminea, D. cneorum, D. juliae.

Dianthuses: D. alpinus, D. superbus, D. deltoides, D. gratianopolitanus ‘Tiny Rubies’.

Erodiums: E. chamaedryoides, E. chrysantha, E. glandulosum.

Gentians: G. acaulis, G. angustifolia, G. paradoxa, G. septemfida.

Irises: I. suaveolens, I. pumila, I. reticulata.

Lewisias: L. cotyledon, L. longipetala, L. columbiana, L. x whiteae.

Penstemons: P. pinifolius, P. baccarifolius, P. deustus, P. procerus, P. caespitosus.

Primulas: P. auricula, P. allionii, P. marginata, P. x pubescens.

Pulsatillas: P. alpina, P. patens, P. turczaninovii, P. regeliana, P. vulgaris and hybrids, P. helleri, P. aurea, P. occidentalis.

Saxifrages: S. longifolia, S. sempervirens, S. fortunei, S. paniculata, S. cotyledon, S. bryoides.

Sempervivums: S. montanum, S. arachnoideum, S. caucasicum, S. calcoreum, S. tectorum. Similar plants in other genera include Orostachys fimbriata, O. spinosa, Prometheum chrysacanthum and Rosularia elymaitica.

Botanical Tulips: T. clusiana, T. batalinii, T. acuminata, T. aucheriana, T. biflora, T. humilis, T. saxatilis, T. sylvestris.

In addition to alpine plants, contemporary rock gardens make use of xeriscape plants, which are all highly drought tolerant once established. Some examples of plants in this group are Mediterranean herbs such as thyme, lavender, rosemary and sage, and plants from the American southwest such as cacti, yucca, sand verbena, and junipers.

Many drought-tolerant plants native to California and Oregon work well in rock gardens. A partial list includes: Oregon sunshine (Eriophyllum lanatum), yarrow (Achillea millefolium and A. formosa), sea thrift (Armeria maritima), mariposa lily (Calachortus spp.), blanket flower (Gallardia aristate), showy fleabane (Erigeron speciosus), coyote mint (Monardella villosa), tufted evening primrose (Oenothera caespitosa), rose sage (Salvia pachyphylla), beardtongue (P. davidsonii var. menziesii and P. cusickii), stonecrop (Sedum spathulifolium), California fuchsia (Epilobium canum), kinnikinnick (Arctostaphylos uva-ursi ), and California poppy (Eschscholzia californica).

My rock garden site is partially shaded, so I’ll need to make use of woodland plants that will blend well with alpines and xeriscape plants. Some of our native irises will fit this bill, including Iris innominata, I. douglasiana, I. chrysophylla and I. tenax. Other native woodland species that can be added to a rock garden are crevice alumroot (Heuchera micrantha), creeping Oregon grape (Mahonia repens), fringe cup (Tellima grandiflora) and foam flower (Tiarella cordifolia).

Non-native woodland plants for a shaded rock garden include small ferns, miniature hostas, dwarf spurges and hellebores.

Of course, these aren’t all the plants that can be grown successfully in a rock garden, but the lists offer a would-be rock gardener like me a lot to think about, and perhaps those with more experience will discover a few new “rock stars” for their gardens, as well.