After leveling the concrete blocks, we filled the bed with a scree mixture of 1/3 each river sand, 1/4" crushed rock and compost.
We used a rough, volcanic rock that has large vesicles and is covered with lichens and mosses. The local rock yard called this rock "Mossy Rock" though it is probably more accurately called scoria.
Lewisia cotyledon, Pasque Flower (Pulsatilla vulgaris), Azorella trifurcata and Shrubby Penstemon (Penstemon fruticosus) thrive in this bed that receives occaisional hand watering in summer and in four seasons has required no supplemental fertilizer. Eventually the compost in the original soil mix will break down and we will need to fertilize.
RAISED BED TWO
We placed landscape cloth at the bottom of this rectangular concrete raised bed to discourage large root intrusion by nearby trees. The small roots of deep rooted alpine plants are able to penetrate into the native soil over time.
The concrete blocks were leveled and each course of blocks alternated for maximum stability.
Corners were filled with crushed rock and 48 " rebar stakes were driven into the ground .
We used a rock called "green granite" obtained from a local rock yard for this bed and capped the edges with slate tiles. We mounded the rock garden mix high and placed the rocks close together to create stable, steep sloping planting areas. Because the rocks and soil are mounded, we created micro-climates with more exposed south and west facing slopes and more sheltered east and north facing slopes. Dwarf conifers planted along the top ridge provide additional shelter to the plants on the back north facing slope.
Raised Bed Three
This concrete block raised bed is created in a quarter circle shape, with a higher back edge and plantings sloping down to a lower front edge. The first step seen here was a rough layout. We went back and carefully leveled each course, alternating block placement, and stabilizing the bed through the use of rebar and roadbed as described in the above example. This was particularly important for the higher areas at the back of the bed.
We mounded the soil high at the top of the bed and worked the mossy rocks in carefully to stabilize the steep slope.
We laid out the planting scheme, placing trailing plants along the edge and crevice plants in spaces between the tightly packed rocks. This is a very warm south facing spot with heat reflected off the building at rear and we made sure to select heat and sun tolerant plants.
Here is a view of the newly planted bed before we capped with pavers.
The wooden structure behind the raised bed is an Alpine Frame.
We capped the edges with pavers to give the bed a finished look although, because of the gaps at the front, it would probably look better if covered with stucco (see below). Plants in this bed include Pine Needle Penstemon (Penstemon pinifolius), Globe Daisy (Globularia cordifolia), Trailing Baby's Breath (Gypsophila repens), Pussytoes (Antennaria dioica), Hens and Chicks (Jovibarba heufellii and Sempervivum arachnoideum).
View an example of a Stucco Covered Concrete Block Raised Bed