Bring that "top of the world" feeling you get from hiking in the mountains to your own back yard with an alpine rock garden.
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Portland, Ore., is the home of mountain man and alpine gardener Scott Vergara. Scott believes the advantage of an alpine garden is that you can grow plants usually found only at high elevations or really dry conditions in different parts of the country with this type of garden.
Large boulders provide the "mountainous rocky look" in an alpine garden, but plants play an equally important part in creating the garden's character. Types of plants found in alpine elevations are usually low-growing specimens that require well-drained soil.
The three structural elements that Scott likes to use in an alpine garden include things that provide lots of color — ground covers, woody plants for textural interest, and flowers such as phlox.
Laying the Rocks
First, establish the back edge of the bed, make sure it's reasonably level and straight. Dig a small trench to set the first course of rock (figure A).
Scott uses large lava rocks to frame out the bed. They're placed in the groove along the backside (figure B). You can use any large rocks, but Scott prefers lava rock that's native to the Oregon mountains.
Next, mix a planting medium designed for good drainage 1 part sand, 1 part pumice and 1 part organic matter. It’s important to make sure that the ground underneath your base line is sloping away so that water will not collect at a low point (figure C).
Use more rocks to set the other side of the wall. The important part here is to leave spaces where you will place the plants.
Now repeat the process of digging and trenching along the front of the garden. The large lava rocks fill in the trench. This part can be challenging becuase you must keep working the rock placement. Roughly lay them in first, then go back and adjust as necessary. Again, it’s important to leave spaces between the rocks because that’s where the roots of the plants will go into the soil.
Once the garden is framed out with rocks, create a slope by dispersing the soil mixture at an angle (figure D).
Use smaller rocks to fill in the bed to create a flowing mountain feel. Remember to bury the rocks a bit so they look established (figure E).
Besides going for the right look, functionality is important as well. Some rocks should be placed vertically to create a shade spot to protect plants from the hot afternoon sun. After all the rocks are placed, it’s time to plant.
Planting the Garden
Place your plants around the rocks first to get a visual idea of how it’s going to work. When you are pleased with the total effect, start planting.
The plants Scott has chosen include a mixture of alpine plants that grow at high altitudes and some common garden varieties that have color throughout the year. They include:
- Dwarf creeping willow
- Stonecrop (Sedum hispanicum)
- Hens and chicks (Sempervivum)
- Dwarf iris
The trick here is that you want really good drainage for the plants. To achieve that, place them a little higher and use very little soil, mostly pumice and gravel.