| A Garden Walk on the Wild Side |
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By Lindsay Bond Totten
Scripps Howard News Service When it comes to plant hardiness, gardeners divide themselves into two camps. Practical types accept their lot and choose specimens hardy to their zone. Dreamers take risks. For them, the thrill of an upset victory outweighs the inevitable losses. Often placed in the position of being asked for advice, I lean towards the former. It seems rather irresponsible to take chances with another gardener's time and money. (There are, I reason, challenges enough without adding foolhardiness to the mix.) When it comes to my own plot, I defected from the "practical" camp a few years ago -- for a blue lacecap hydrangea. Spurred by an irresistible attraction and encouraged by warmer winters, the zone-and-a-half chasm between us was deemed surmountable. I delight each summer when a few spindly blossoms appear. But I don't kid myself: Any self-respecting gardener in Zone 7 would surely replace this particular blue lacecap hydrangea with a more robust specimen. Nonetheless, I'm satisfied with it and have begun searching for a niche for nandina, another Zone 7 plant that I covet for its architectural qualities. Most of my garden rests squarely in the heart of USDA Zone 5b. But there are pockets -- called microclimates -- that stay warmer. Some are mitigated by man-made objects, like walls; others just occur naturally because of the topography. The blue lacecap hydrangea survives in one of those special places. Every garden has them. And pinpointing these microclimates entitles a gardener to sample another zone's treasures. Half a zone (say from Zone 5b to 6a) is a relatively easy stretch. A full zone is more challenging. A zone-and-a-half is precious, indeed. If you find such a spot, don't squander it. Here's where to look: - On the leeward side of a natural windscreen: Wind is the enemy in winter. Strong winds lower the ambient air temperature and desiccate delicate plant tissues.
Tall conifers and thick evergreen hedges deflect the wind, as it passes up and over their branches. At their feet is created a pocket of relative calm. Coupled with a thick organic mulch, this windscreen is often good for half a zone. The taller the plants that make up the windbreak, the further the protected area will extend from the drip line of the presiding evergreens. - South-facing slopes or berms: The soil of south-facing slopes absorbs the maximum amount of sunshine on fine winter days. Notice that the snow always melts here first and the grass greens up earlier in spring than in other areas of the garden.
As cold air slides downhill on late winter mornings to settle in "frost pockets" at the bottom of a slope, plants on the south-facing incline just above frequently escape those cruel frosts by a narrow two or three degree margin. It can be just enough. The danger, of course, is that tender plants growing on such a sunny slope may be tricked into leafing out prematurely in spring. Be ready to cover them if a hard frost threatens. - A niche enclosed by plantings: We build garden "rooms" for the sense of enclosure they inspire, but they can also provide a safe haven for moderately tender plants. Within the "walls" of such a space, the heat of the day dissipates more slowly in the evening than it does in the surrounding landscape. Wind is also less likely to challenge precocious leaf buds.
Create garden rooms with clipped hedges, informal shrub borders (include plenty of evergreens), fences, arbors, or vine-covered lattice. Tall plants with dense foliage afford the greatest protection. - At the base of walls and boulders: Stone absorbs heat during the day and releases it slowly at night. Demonstrate by touching a large boulder a few hours after the sun goes down. It's still warm.
Capitalize on this "heat sink" (you can see just how far it extends by where the snow melts on a cold day) by tucking tender plants at the foot of a boulder or wall. Plant size will depend on the height and orientation of the stone -- south-facing walls capture the most heat. Best-case scenario: a full zone of protection. - Protected spots next to buildings: Structures and pavement act as "heat sinks," too. That's why temperatures within urban areas are often elevated compared to the surrounding suburbs.
Experiment in beds right next to house or garage. Buildings and sidewalks will wrap plants in a blanket of warmth; high walls will shelter them from the wind. Fortunate, indeed, are gardeners with courtyards, created by an L- or U-shaped house and enclosed on the open sides with walls and fences. The gardens within can flaunt plants that have no business surviving there. (Lindsay Bond Totten, a horticulturist, writes about gardening for Scripps Howard News Service.)
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