Gardens with Rocky Hillsides

If you can't beat it, enhance it. A rock garden is a great way to handle a sloping front yard, or to artfully plant any hillside. Rock gardens showcase the natural beauty of stone as well as plants. A well-constructed rock garden will look as if it has been there forever, especially once the rocks are clothed in care-free plants. You can choose any style for your rock garden, from an informal tumble of stones to a simple garden built around existing ones. If you need to stabilize the slope, add small, stacked-stone retaining walls backfilled with good soil. They'll serve the additional purpose of creating more planting pockets for plants, particularly suited to those that require perfect drainage.

Choose local stone so that it blends in seamlessly with the surroundings, especially if you are adding rock to an existing outcrop. Consider the options. Weathered, uncut stone gives a more natural look, while cut stone creates a more formal mood. Garden artistry enters in when you mix and match a variety of plants with the stone. The most successful formula is to balance nearly equal areas of stone and plants, so that the soft textures of the foliage and the flowers are framed and flattered by the heavy, smooth surfaces of stone.

Placing Rocks

In order to make the most of an existing stone outcrop, first, clear away all of the unwanted vegetation. Then add additional stones if needed to create a balanced look, starting at the bottom of the slope and working upward. Choose the largest, heaviest rocks for the base of the slope, and work upward, decreasing the size of the rocks as you go. This is a trick of perspective that makes use of the way things at a distance naturally look smaller than the same objects would if they were close by. Putting successively smaller rocks at the top of the hill will increase its perceived height. To make the stones as stable and natural looking as possible, dig out places for the stones and position them so they are half buried in the soil. When working with stones that are somewhat flat in shape, place them so that they tilt backward toward the slope. This trick encourages water to flow back into the soil behind the stone where it will benefit plants tucked into planting pockets.

Soil for Rock-Garden Plants

From a plant's point of view, the outstanding characteristic of a rock garden is the superior soil drainage it provides. So it stands to reason that most rock-garden plants thrive when planted in a mixture of one part soil, one part rich compost, and one part coarse sand. Mix the soil for planting pockets in advance, so it will be ready as you place the stones. Use the amended soil to make little beds or to fill nooks and crannies where you will later place plants. Wedge the soil mix into deep crevices or broad pockets between stones, poking about with a spade handle or metal rod to eliminate hidden air pockets.

Many rock-garden plants creep or cascade, forming low carpets of color between stones. To avoid a patchwork look, group similar-looking plants together so they'll interweave as they mature. Shrubs can become an integral part of the scene. But, when planting shrubs among stones, keep the root ball level and the crown of the shrub upright. Small planting pockets are perfect places for clusters of little bulbs like miniature daffodils, squill, or grape hyacinths. Where the layer of soil is shallow, such as atop large stones, plant the area with shallow-rooted, hardy succulents, such as stonecrop and hens and chicks. Most
rock-garden plants eagerly spread to fill in vacant places, but until they do, you will need to patrol the area periodically and pull weeds by hand. As your plantings mature, occasional trimming of plants to keep the scene neat, and the stones visible, becomes an important yet enjoyable task of nurturing a hillside rock garden.

Finishing Touches

After the rock garden is planted, water it gently to keep from dislodging plants, and water it thoroughly. It takes several passes with a hose outfitted with a sprinkler head to wet the soil in crevices between the rocks. Afterward, apply a 1 in (2.5 cm) thick mulch of pea gravel or fine pebbles. This type of mulch allows water to filter through freely to plant roots, but it does a good job of holding soil and roots in place. It also keeps foliage high and dry, and that's just what rock-garden plants prefer.