On a 7,200-foot-high hillside above Basalt, Colorado, grapevines burgeon despite snowy winters and short summers. Two-thousand feet lower, in a south-facing, sloped Denver yard, desert denizens yucca and manzanita bloom. And in between, on the east side of a Boulder house, a European dogwood bursts into soft yellow blossoms while winter still holds sway.
Your state – and even your property – is full of microclimates, though their extremes may not be as far apart as those of the West. Temperature, precipitation amounts, seasonal changes, humidity and soil properties can vary county to county, street to street and house to house – and more importantly, within your own fence line. Even a condominium balcony can have microclimates.
Getting to know those quirks like an old friend can be the key to gardening successfully, not just a reason to gloat as your south-facing, exposed driveway shrugs off a five-inch snow that your neighbors down the road have to dig out the heavy machinery to remove.
While Western microclimates are pronounced, they offer a model for any homeowner to contemplate. Horticulture experts recommend taking a while to get to know your site before planning any major landscape or crop investments. Notice where the snow stays longest, which low spots become waterlogged and which are well drained. If you have walls, terraces or rock ridges, check how warm they become at the height of summer – and how cold they get in winter. As well as assessing the range of temperatures, scope out how early in spring things warm up and how late into fall they stay warm. Will future beds be shaded by evergreens, or allowed to bask by deciduous trees that lose their leaves in winter? Take stock of seasonal shade, wind protection (or lack thereof) and any heat-reflecting walls.
Denver Water, the city utility, is famed for having coined (and trademarked) the concept of xeriscaping during a period of drought combined with sudden population growth. Xeriscaping refers to gardening with plants that are highly adapted to low-water conditions. But basically, xeriscaping is a specialized form of microclimate gardening. It takes into account that Colorado’s Front Range is a high desert that experiences weeks of little rain during summer. Such gardens can be beautiful – if the gardener chooses tough plants.
Irene Shonle, Colorado State University extension agent for the state’s high-altitude Gilpin County, watches microclimates play out every year in her roses. A tough Canadian cultivar that’s supposed to be hardy to Zone 2 but lives on her home’s northwest side gives her maybe 10 blooms a year, she says. Meanwhile, a white rose that’s sheltered from the roaring mountain wind blooms spectacularly.
“The wind curls around the house and dumps its payload of snow there because it’s been slowed,” she says. That snow bank, in addition to carrying precious water, insulates and protects her rose from the winter cold. Shonle’s district ranges in altitude from 8,000 to 10,000 feet – “and we can see 13,000 from here” – so it’s a place where one would expect microclimates to be extreme.
Jerome Ostenkowski, founder of the Central Rocky Mountain Permaculture Institute, is able to harvest apples and grapes – and many other plants you wouldn’t think are adaptable to high altitudes – in a forest garden above Basalt, near Aspen, at roughly 7,000 feet. He’s been able to grow a diverse, food-producing garden along a system of terraces and walls.
“When the rock heats up, all the beds retain that heat within them. You can start growing a month earlier, and then you get a month on the other end,” he says.
But microclimates can be equally extreme in urban Denver. Travis Beck of Eco-Savvy Designs LLC was faced with a nearly 45-degree south-facing slope that formed the front yard of a Denver home. Those angled, south-facing surfaces magnify summer heat and minimize winter cold.
Or, as Beck puts it, “With the reflective heat and thermal mass, it baked there. It really baked.”
Instead of fighting the microclimate to install the New Zealand flax that the residents loved, he persuaded them to go with a similar foliage form supremely adapted to that mini-environment.
“What we wound up using was a whole variety of yuccas, including one called ‘Bright Edge,’ with lots of yellows and reds mixed in, a couple of manzanitas and one cliff rose. I recently went back to check it out, and they looked quite happy and healthy with no irrigation. The idea was to plant something that, once established, they could just ignore.”
But in an east-facing yard in another neighborhood, Beck was able to indulge a completely different aesthetic. “We were able to grow a nice variety of xeric, but not super-xeric, plants, such as variegated iris and peonies.” The protection from the wind, hot afternoon sun and the temperature buffering of an eastern exposure, Beck says, “allowed a fuller, lusher garden than you’d have ordinarily.”
Microclimates are more complex than spinning a compass, however. Not all homes are oriented on a classic north-south-east-west axis. In urban Denver, which sits in a valley, most of Beck’s clients don’t face the howling, plant-desiccating wind that can dry up shrubs out on the plains or in the foothills.
Alison Peck of Matrix Gardens in Boulder has worked in passive solar and energy conservation and says planning a garden requires attention to not just the big house-rattling winds “but also the gentler winds. They don’t create problems, but they’re something to pay attention to when you’re trying to capture heat. Blocking the wind helps to retain heat.”
Breezes can also dissipate heat – a boon if your landscape includes places for people. In the warmer southern states, she says, “you don’t want to put a porch on the south side unless you have really good shade.” Ideally, Peck advises having several different outdoor spaces: “north for summer and southeast for spring, fall and winter. A southeast porch is protected from the cooling wind and catches the morning sun.”
In a non-ideal situation, she says, use plantings, a wall or a fence to create a nook that has some wind protection. For south-facing areas, she advises planting solar shade trees that allow warming by the winter sun but leaf out in time to protect the area in late spring, summer and fall. Designers warn that gardeners can get completely focused on a particular tree or plant they want to have as they plan a new garden in the spring. But they forget about the neighbor’s huge shade tree that will leaf out in a month and block most of the sun from a patch they’re envisioning for tomatoes. Even the shadows cast by buildings vary from season to season.
Think of microclimates as multidimensional. When she assesses a site, Ingrid Earnst, owner of Ingrid’s Landscape Design in Boulder, takes into account not just wind, sun and altitude, but water, pavement, rock areas and how much development is in the surrounding area. “I have about 30 questions that I ask clients,” she says. Then she goes to the site to see for herself: Is there a body of water that goes through the property? How is the house situated? What plant material is on the site now – and what is on the adjacent sites?
If your property is hilly, Earnst says, you have to check for cold sinks, where chilled air rolls down slopes and collects in low spots. Columnar junipers or other evergreens can provide a shield from the wind of hilly sites. But even in providing windbreaks, “you have to think about how you will change the climate because of the sun.”
Once you understand your property’s microclimates, you can reap a harvest of delight. Earnst especially cherishes her Cornelian cherry dogwood – planted on the south side of the house one January when the soil didn’t freeze.
The tree now serves as her first herald of spring, even before the crocuses pop up. “It’s almost never frozen there,” Earnst says. “I was taking a risk, but I just couldn’t wait.”
Susan Clotfelter writes about food and gardening for The Denver Post and blogs atwww.DenverPost.com/digginin.