Regional Gardening Reports :: National Gardening Association

In the Garden:
Pacific Northwest
April, 2012
Regional Report

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I love the unique flowers and attractive foliage of this abutilion. I take mine indoors over the winter months as a precaution against our sometimes snowy winter weather.

Has Your Gardening Zone Changed?

Have you seen the USDAs new Plant Hardiness Zone Map? The map was updated this year, not so much because of climate change but more as a reflection of newer satellite imaging technologies and the analysis of weather data collected over a longer period of time than was used in older map. The older map, published in 1990, was based on temperature data recorded from 1974-1986. The new map uses data measured at weather stations during the 30-year period between 1976 and 2005. The resulting temperature changes are small, but many gardening zones have changed, with some being upgraded a half-zone warmer or downgraded a half-zone cooler. The new map ( is interactive, and you can hone in on your own gardening zone by entering your zip code. If you check out the map you may even find you're gardening in a microclimate, with temperatures slightly warmer or cooler than your gardening friends living just a few miles away.

Microclimates are areas within a neighborhood, or even within a single garden, with patches of ground that are a few degrees warmer or cooler than their general surroundings. These areas can also be wetter or drier. Microclimates can be found in even the smallest of yards. In fact, it's hard to find a garden without at least one. A hedge, a stone wall, or even a building can alter the immediate setting enough to create a microclimate. On a sunny day, a dark-colored house may radiate enough heat to make a nearby tropical plant feel right at home, even here in the Pacific Northwest. If only a degree of temperature can change cold water into ice, think what a couple of degrees can do for your plants.

Identify Your Microclimates
You can identify microclimates in your landscape by watching where frost first appears or where snow lingers the longest. These are the coolest pockets. In my garden, where the snow melts first, the bulbs bloom first. Elsewhere in the garden, similar varieties of bulbs bloom several weeks later.

I've noticed the same behavior from my two lilacs. The one planted out back flowers a week or two later than its twin in the front yard. The lilac out front is near our driveway, which retains and radiates enough heat to create a warm spot. This particular lilac responds to its microclimate by breaking dormancy sooner and blooming earlier in the season.

Even if your garden doesn't regularly get snow, you can identify microclimates by watching for those places where bulbs bloom first or last, or where new shoots or spring growth appear earliest or latest. Taking advantage of warm spots can mean enjoying spring a few weeks earlier or making your favorite blooms last longer.

Making Use of Microclimates
Anything from a hillside to a paving stone can warm (or cool) a patch of soil enough to create a real advantage for plants, especially at the far ends of the growing season.

I extend the blooming season by planting bulbs in both cool and warm spots. I've also found that a wind-protected southern exposure provides just enough extra warmth to shelter a perennial in a zone colder than its rating. But because plants in warm spots sprout earlier, they are more vulnerable to late-spring freezes. To increase their chances for survival, I add a thick layer of mulch in late fall and remove it in early spring. If frost threatens, I replace the mulch material, or cover the plants with pine boughs to get them through the chill.

Getting to know your garden is an exercise in observation (and involves copious note-taking). Once you begin to understand its subtle hints, you're well on your way to reaping the benefits of its microclimates.

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