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Planning a Rock Garden
Parts of New England are famous for rocky landscapes and poor, thin soils. If you have a landscape filled with stone outcroppings and rocky soil and you’re not quite sure what to do with it, a rock garden might be just the solution for you. Representing in miniature the landscapes of mountain slopes, coastal bluffs and high plains, rock gardens can be filled with traditional small-growing alpine plants or with diminutive forms of familiar bulbs, perennials and shrubs. Whether you take advantage of a naturally occurring rocky landscape or decide to create one from scratch, rock gardens require planning to look their best.
Location, Location, Location
Rock gardens usually incorporate some sort of slope, mainly to encourage good drainage. However, in larger landscapes, rock gardens may have a variety of areas, with level ground and even a small pond or trickling stream.
Many rock garden plants enjoy a sunny location, but they do best if not exposed to full sun all day. Provide some sort of shelter from full sun. Overhanging limbs of small shrubs or the shadow cast by larger boulders can provide relief from summer’s intense sun or the cold winds of winter. Remember that many of the plants originating in alpine areas are protected from cold winds and full sun by a blanket of snow.
To make your rock garden seem as natural as possible, locate it away from artificial surroundings. Avoid backdrops like garages, houses, driveways, and formal gardens. Tuck your rock garden away in a secluded area of your backyard, if possible. An air of informality will help you relax and unwind.
Like any good garden, rock gardens should be designed on paper before heading out into the backyard with a shovel. Take some time to sketch several designs, trying out one or more locations where you would like your rock garden to be. Incorporate your yard’s existing boulders and outcroppings in sketch. If you need to bring in boulders and stones to build your rock garden, make sure to use several different sizes and shapes. And don’t use too many—you don’t want your rock garden to look like a rock pile.
Remember the garden shouldn’t be too wide that you can’t reach a plant without stepping on another. If your space seems wide, incorporate a winding path from which you can access those hard-to-reach corners.
You may also need to terrace a very steep slope to ensure the soil won’t rush down the hill during a heavy rain. Terracing with stone will allow you to plant additional plants in the nooks and crannies created by the wall.
Equally important is to avoid forming areas where water collects easily. Rock garden plants are susceptible to wet conditions, and pools may cause your plants to rot.
Rock garden soil is traditionally poor, thin soil but its most important characteristic is good drainage. Even if you have good-draining soil, you’ll want to prepare a batch of soil mixture to fortify your garden. One recommended mixture incorporates equal parts soil, course sand, and peat moss or compost. Most rock garden plants do well with soil in a pH range of 6-8. Adjust if necessary with an alkaline amendment.
To make sure your plants get off to a good start, remove the soil currently between your existing outcroppings and replace with the rock garden mixture. Or, construct your own arrangement of rocks and stones in a plot prepared with this soil mixture. Use small gravel or stone-chip mulch around your plantings to keep out weeds and help the soil stay moist.
Like any garden, the plants in it should reflect personal favorites and styles. There are plenty of resources in the MHS Library and on the World Wide Web that list rock garden plants and where to purchase them. Take some time, look through the references and catalogs, and choose those that catch your eye or suit your lifestyle. Beginning rock gardeners may want to start off with easy-care items, working their way up to finicky plants needing lots of love.
Plant into moist but not very wet soil. Firm the plants into the soil to remove any air pockets surrounding the roots. And be creative when planting! Group them in threes, placing smaller plants in crevices and larger shrubs near bigger rocks. You’d like your garden to look as natural as possible, so stay away from planting in straight lines.
Designed and installed correctly, rock gardens can be low maintenance. With proper mulching, weeds can be kept to a minimum. Prune dead leaves and flowers to keep the plants looking fresh. Soil in crevices will need to be refreshed about once a year to keep the alpines in top form. Spring and fall will require a bit more work—readjusting plants heaved by frost, topdressing, and applying and removing a light, airy winter mulch. Your garden visitors will be duly impressed!