Home & Garden

Build your own rock wall for the garden

By: Jennifer Bennett

Author: Canadian Living

Home & Garden

Build your own rock wall for the garden

By: Jennifer Bennett

Stonework gives any garden -- country or city, spacious or small -- a feeling of permanence and calm and provides beautiful "bones" around which to arrange your plantings. Joanna Atherton's award-winning garden north of Kingston, Ont., is one of the spacious sort. It's half a hectare or so of retaining walls, terraces, paths and freestanding rock walls that support hundreds of shrubs, perennials and rare alpine plants.

DIY project: Build your own rock wall in your garden
Amazingly, all this stonework was built by Joanna herself. It suggests hours of backbreaking labour, but Joanna insists that working in her garden is sheer relaxation, even meditation. "You get kind of addicted to it," she says. "You absolutely cannot think about anything else when you're doing it."

Her husband, David, gathers the largest boulders from their farm with his tractor, but after that it's up to Joanna. "The stonework is a major part of my garden," says Joanna, "but the beauty is that once it's done, it's done."

Her retaining walls are used to terrace a long slope and to surround raised beds. These elevated beds ensure the perfect soil drainage that most alpines require and raise the small plants up where they can be more easily seen and tended. They also offer crevices of soil and patches of shade for tender roots. And they're still standing firm after several Zone 4 winters.

Useful tips
Here Joanna shares her tips and step-by-step instructions for stacking a stable wall to surround a raised bed. If you feel inspired but don't have a large-scale site, remember that even a tiny town house patio could accommodate a rock-walled alpine, herb or perennial bed.

Joanna's stoneworking smarts
Where to find stone
• Freestone (also called drystone) walls are held together by weight and gravity, not mortar, and to build one you'll need natural stone. Unless, like Joanna, you live on a large property in a rocky area, you'll need to look under Stone in the yellow pages to find sources such as quarries, stone yards, nurseries or building supply stores. Some farmers will also sell stone on a pick-your-own basis. Resist the urge to pick up roadside freebies; some municipalities have stiff fines for this practice.

• Determine the desired height (for safety's sake, consult a professional for any wall over 60 cm/2 ft tall) and length of the wall, then consult sales staff when estimating number of stones required.

Page 1 of 2 -- Learn how to choose a stone and stack it up in your garden on page 2

What kind of stone should you choose?
• Limestone cut into rectangles (rundle rock, quarried in Canmore, Alta., for example) or split into flagstones is easy to work with. Sandstone and shale are also relatively flat and simple to use for beginners. Round or irregular granite boulders are extremely durable but harder to place and secure.

• Choose carefully -- stonework should belong in its surroundings. Locally quarried rock, if available, naturally looks at home.

• Match the scale of the rocks to the scale of your house and garden: For instance, large, round boulders or craggy, irregular stones can overpower a tidy bungalow with a neat garden. Also match the style: Low flagstone walls may best accentuate the horizontal lines of a long ranch-style house, for example.

• You may also marry stone to plants. Use granite boulders to border a bed of acid-loving plants such as ferns and heather and mulch the bed with granite pea gravel. For lime-loving plants such as gypsophila and sempervivum, use limestone for the wall and mulch with limestone scree (small, sharp chips). Tufa, a porous, weathered limestone can be used to hold tiny plants in its cracks and pockets. (Most perennials and dwarf conifers will thrive alongside either rock type.)

How you stack up
• Wear sturdy shoes and gloves and be prepared for heavy lifting. Begin by sorting stone according to size so it's easy to find what you need as you build. Sort out any stones with curved or right-angled edges to use where wall turns a corner.

• Next, use strings and stakes to mark the footprint of your planned wall on the ground; inside it, dig a trench deep enough (dig down 25.5 cm/10 in or to bedrock or hardpan, whichever comes first) and wide enough for the first course (layer) of stones, the “grounders” (these biggest, flattest rocks will sit entirely below ground). Lay the grounders, edges tight together and broadside down. Use a 2-ft carpenter's level to check the base of the trench (and as you work, to check that each course of stones is as level as possible when using irregular fieldstone).

• Continue building the wall, one course at a time. For strength, bridge the vertical cracks in the course below (think of a brick wall). If necessary, shim cracks between courses with stone chips (don't use soil; it can promote frost heave).

• Gradually slope the wall inward (toward planned bed) as you build upward, about 2.5 cm (1 in) for every 30.5 cm (12 in) up, using smaller stones for each course, then lay a final course of capstones that extend into the bed approx 15 cm (6 in).

Filling the bed
• Joanna suggests a mix of equal parts topsoil, peat moss and pea gravel, limestone scree or builder's sand.

• Shovel the soil mix into the bed, filling 10 to 15 cm (4 to 6 in) thickness inside the wall with stone rubble, combined with some of the soil mix, to promote drainage.

• Here and there, tuck a small amount of soil into crevices, then tuck in plants such as dianthus, lewisia or saxifraga.

Weathering the wall
In a blender, mix a handful of moss with a bottle of beer, the same amount of buttermilk and a pinch of sugar. Spread the mixture over the rocks; keep it moist to encourage the growth of moss and lichen.

Easy alpines
• Compact and sturdy, alpines survive exposed sites and harsh environments.
• They prefer a very lean soil, so fertilizing is unnecessary.
• More likely to suffer from too much water than too little, alpines require watering only after a period of drought.
• Mulching the beds with gravel keeps weeds down; topping up the mulch every spring keeps the garden neat.

Page 2 of 2

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