This past weekend, the American Penstemon Society held their annual meeting in Boise, Idaho. I was fortunate enough to attend their meeting and join them on one of their field trips. We visited Mores Mountain in the Boise National Forest, which is a short drive north of Boise. The hike was so much fun! There were tons of great plants to see, and the views from the top were incredible. My favorite sights were all the magical rock gardens that were scattered along the trail which were loaded with a diverse number of small plants eking out an existence on lichen splattered outcrops. If you ever find yourself in the Boise area, this is a spot that I am certain you don’t want to miss.
Rock Garden on Mores Mountain, Boise National Forest
Lewisia sacajaweana, Sacajawea bitter root
Ceanothus velutinus, snowbrush ceanothus
Penstemon humilis, low penstemon
Penstemon fruticosus, shrubby penstemon
Calochortus macrocarpus, sagebrush mariposa lily
Calochortus eurycarpus, white mariposa lily
Recently I helped build and plant a rock garden. It was a first for me, but something I had been wanting to do for a while. Rock gardens consist of plants that grow in rocky environments, such as rock outcrops on mountains or accumulations of rocks at the bases of cliffs or steep slopes. Rock garden plants are commonly called alpine plants – alpine refers to an environment that is very high in elevation or, in other words, in mountains above the tree line. Not all rock garden plants are native to alpine environments; however, in the rock garden community, the term “alpine” often refers to small, hardy plants that are ideal for rock gardens.
A rock garden mimics the environments of alpine plants by incorporating a mixture of large and small rocks placed in an aesthetically pleasing manner. Well-draining soil is brought in to fill the spaces between the rocks, and the plants are planted in these spaces. Rock garden plants are typically small and compact. Cushion plants (Silene acaulis, Saxifraga spp., etc.) are one example of a type of rock garden plant. Other popular rock garden plants include the following genera: Pulsatilla, Viola, Sedum, Daphne, Delosperma, Dianthus, Thymus, Primula, and Scutellaria. The list goes on. Many rock garden plants can be found at local garden centers, while others will require some searching, but there should be enough of them available to at least get you started.
A rock garden doesn’t have to mean a scattering of rocks laid out on the ground. They can also be built in raised beds or they can consist of a series of troughs or planters. Rock garden troughs are typically made of tufa or hypertufa. Tufa is a naturally occurring variety of limestone. Hypertufa is a human-made version of tufa that is composed of various aggregates cemented together.
To learn more about rock gardening and to join a community of rock gardeners, check out the North American Rock Garden Society, and stay tuned to Awkward Botany for future posts on rock gardens.
Here is an example of a rock garden in a hypertufa trough. You can see this and more like it at Idaho Botanical Garden.