When choosing plants and landscaping this spring, consider the Washington area's warmer weather pattern, according to plant experts who pointed to a higher average minimum winter temperature in the U.S. Department of Agriculture's revised 2012 planting zone map.
Scott Aker, head of horticulture at the U.S. National Arboretum, said the average minimum is not, by definition, the lowest temperature possible, and no one is saying the area will never see 10-below-zero winter temperatures again. In fact, it may be more difficult now to grow borderline hardy plants because there likely will be more temperature variability, which is more stressful to plants than a uniformly cold winter.
Winter also might be the wrong season on which to focus, Aker said, because "our constraint is quickly becoming the summer rather than the winter."
Because warm weather is starting earlier, he advised getting out in the yard to start planting in March. Not only is it possible, it is necessary, because plants that cannot tolerate heat will not last as far into the summer.
Changes in the average range of temperatures during the day will also affect gardening.
"There's very good evidence that, particularly in our cities, we're not cooling off as much at night in the summer," Aker said, "and that has a profound effect on plants."
Pansies, for instance, cannot tolerate high night temperatures and likely will soon be suitable only for the fall gardening season.
To help deal with longer periods of dry weather, gardeners can work to improve water efficiency, said Ann English, RainScapes program coordinator for Montgomery County.
Group together plants with similar water needs, she said, and locate beds that need more water where they are easy to reach with a garden hose. Add a mulch layer to help retain moisture.
English said learning about plant communities -- or which plants come from the same habitat -- can help when grouping plants based on similar needs.
"Those types of plants tend to look good together; they take the same soil pH, the same kind of moisture, the same kind of exposure," she said. "You just simplify your life."
That does not mean limiting garden choices to only native plants. English said the real issue is finding plants with the necessary characteristics, "like deep roots that soak up a lot of rainwater."
Gardeners who grow plants in pots should allow for the fact that containers dry out quickly, so plant choice will be especially important.
Aker said the container gardens at the arboretum now are mainly succulents, or plants that are thicker or fleshier to retain water in dry climate or soil conditions.
"In many ways, they're more beautiful than things like coleus that demand a lot of water," he said.