Most gardeners may go through the rose-and-peony stage, but rock gardens, Marion Jarvie believes, are "where many of the great gardeners end up." Why? "In a rock garden you can gather together all of the things you've really loved in a miniature landscape of trees, shrubs and perennials," she says. "You're working with it all -- sand, soil and rocks, form, colour and texture -- in an environment that you can control. You can even create small boggy areas and mini microclimates. And unlike a typical perennial bed, a rock garden doesn't go underground for the winter. The plants are tough and tailor-made for Canadian conditions."
Any visitor to Jarvie's garden in Thornhill, Ont., just north of Toronto, can find evidence of this great gardener's explorations and how she's ended up where she is. Born in Britain and a gardener from childhood, Jarvie moved to the property almost 30 years ago. The 30-by-26-metre back garden was a flat, windswept hilltop within plain view of a dozen neighbours. And in winter this patch of "waterlogged clay" was occasionally objected to -38°C temperatures.
It's now a leafy, serene and almost secret garden, surrounded by a dense green wall of clipped cedar. Looking south from the terrace behind the house, you see the magnificent borders of the garden: raised perennial, shrub and woodland beds that circle partway into the central lawn and finish with a low-lying bog garden and pond.
The magic of scree
The jewel in their midst is Jarvie's special joy, an undulating scree garden covered in silvery shards of stone, patterned with quiet greens, greys, purples, reds and golds. Not a standard suburban "rockery" -- often a bank with rocks and petunias tucked into it -- hers is a carefully constructed yet naturalistic rock garden containing more than 100 genera of plants, including more than 30 dwarf shrubs (only 50 per cent flower) and 15 types of grasses. The limestone scree (small, sharp chips) provides the quick drainage and alkaline environment that alpine plants need. Suited to barren, cold and windy conditions, they are perfectly situated in this garden, which has constant air circulation and spots that dip down to Zone 4.
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Jarvie's garden design
The scree garden stretches 12 metres across the yard and, in places, is 7.5 metres deep from front to back. Jarvie used a full dump-truck load of sand and one of gravel to build up the bed over compost. Then came the planting.
She favours woody plants, subtle variations in colour and texture and varying shapes (soft, spiky, flat and full). A true collector, she exults that in the space required by an average adult peony, 50 alpines can happily coexist. Primarily interested in foliage, Jarvie often chooses plants such as the variegated Daphne 'Carol Mackie' that have clusters of ever "blooming" rosettes. Alongside rare plants, she has planted some scaled-down versions of familiar species, including Pinus parviflora 'Adcock's Dwarf' (the smallest pine), Dicentra eximia (a compact bleeding heart) and Fuchsia magellanica (a dwarf fuchsia that usually needs overwintering indoors).
Jarvie, who propagated plants at a commercial nursery for 11 years and taught courses in city gardening and landscaping at George Brown College in Toronto for 10 years, has become fascinated by dwarf alpines. Between giving lectures, designing private gardens and propagating rare species in her greenhouse, she now spends several months each year travelling to remote and rocky mountainsides to photograph these hardy, high-altitude gems.
Start your own scree garden
To replicate alpine conditions, choose a sunny, airy spot. Steer clear of sites along south-facing walls or banks; alpines so situated can cook in strong afternoon sunlight. Instead, Jarvie recommends, choose a site or create a bed that slopes down to the north and/or east. If bedrock breaks through your yard, build a bed around it.
Water flow is key
Good drainage is the single most important requirement for a successful scree garden. So along with sun and "buoyant air," you need "lean soil." Here is Jarvie's recipe: Start with a separate layer of rich compost for the bottom third of the bed. On this, spread the top two-thirds: a 1:1 mix of limestone scree (such as six-millimetre Aberfoyle grit) and coarse builder's sand. Make your bed at least 35 to 45 centimetres high (it will settle slightly). Contour gentle hummocks and hollows, but, she cautions, avoid creating a mini Matterhorn. Cover with a thin layer of scree.
Consider the elements
As you work, consider climate, prevailing wind and the eventual placement of your plants. Make small mounds on the windward side to shield any alpine that is borderline for your zone. And to protect sensitive plants, try Jarvie's trick of burying a large "antishock" rock right down inside the earth, then nestling plants around and above it. If the mercury does a quick dive, the rock radiates heat as it slowly cools (the converse is equally true), ensuring a gradual temperature change for nearby plants. Jarvie has warmed up her garden to Zone 7 in spots.
Log your garden progress with a garden journal.
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Scree gardens are not built with boulders, but Jarvie does sparingly use large one-person-size rocks (ones that are small enough for a single person to roll) and, more generously, scatterings of small pebbles to add surface variety and interest. To find rocks, ask around: some farmers sell them on a pick-your-own basis. It may be tempting to raid road allowances and parks, but don't. Many municipalities have steep fines for this practice.
Choose plants with care
When choosing plants, pay attention to the colour, texture, height and growth habit (vertical, cushion or matforming, etc.) of the foliage. Most alpines bloom only briefly and you want your bed at its best all season. Choose dependable and accessible plants to begin, then move into more expensive and exotic varieties as your experience grows with your garden. If a plant isn't successful in one spot, try it in another, but remember that many alpines are naturally slow-growing. Jarvie's Tsuga canadensis 'Minuta,' for example, has achieved a 10-centimetre diameter over 10 years.
(Click here to learn about herbs to enhance your scree garden.)
Gardeners who are confined to a terrace or balcony can adapt Jarvie's instructions to make small scree gardens in urns or troughs (no winter protection is needed). She notes that more than 100 members of the Manhattan chapter of the North American Rock Garden Society, one of whom came second in a mid-1990s competition, are container-only gardeners.
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