Soil For Rock Gardens: Information On Mixing Soil For Rock Gardening

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By Mary H. Dyer, Master Naturalist and Master Gardener

Rock gardens emulate rocky, high mountain environments where plants are exposed to tough conditions like intense sun, harsh winds and drought. In the home garden, a rock garden generally consists of an arrangement of native rocks, boulders and pebbles with carefully selected, low-growing plants nestled into narrow spaces and crevices.

Although rock gardens are sometimes located on sunny, open areas, they are often created where they add beauty and stabilize the soil on difficult slopes or hillsides. Speaking of soil, what can be found in a rock garden soil mixture? Read on to learn more.

Soil for Rock Gardens

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If you’re creating a rock garden on level ground, begin by marking the perimeters of the garden with spray paint or string, then dig down about 3 feet. Soil prepping a rock garden bed consists of creating three separate layers that promote good drainage and a healthy foundation for your rock garden plants. Alternatively, you can mound soil to create a raised bed, berm or hill.

  • The first layer is the rock garden’s foundation and creates excellent drainage for the plants. This layer is simple and consists of large chunks such as old concrete pieces, rocks or chunks of broken bricks. This foundational layer should be at least 8 to 12 inches thick. However, if your garden already has excellent drainage, you may be able to skip this step or make a thinner layer.
  • The next layer should consist of coarse, sharp sand. Although any type of coarse sand is suitable, horticultural-grade sand is best because it is clean and free of salts that may harm plant roots. This layer, which supports the top layer, should be about 3 inches.
  • The uppermost, all-important layer, is a soil mix that supports healthy plant roots. A good rock garden soil mixture consists of approximately equal parts good quality topsoil, fine pebbles or gravel and peat moss or leaf mold. You can add a small amount of compost or manure, but use organic materials sparingly. As a general rule, rich soil isn’t suitable for most rock garden plants.

Mixing Soil for Rock Gardens

Rockery soil mixes are as simple as that. When the soil is in place, you’re all set to arrange rock garden plants such as perennials, annuals, bulbs and shrubs around and between the rocks. For a natural appearance, use native rocks. Large rocks and boulders should be partly buried in the soil with the orientation of the grain facing the same direction.

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