New plant hardiness zone map means changes for mountain gardeners
February 12, 2012
If you grow any plants in Colorado, your zone is everything!
The USDA has just released the 2012 Plant Hardiness Zone Map that could put you in a whole new zone.
What is a hardiness zone?
The USDA’s zones are based on the average low winter temperature for an area. In Colorado, our zones range from the cold Zone 3a (-40 to -35 degrees F. ave. low winter temp) to our warmest Zone 7a (0 to 5 degrees F. ave. low winter temp). Across the United States, many areas have gone up to be one-half zone warmer. But USDA cautions this is often less about global warming than it is about more accurate monitoring of temperature data. And in mountain areas, because we now have better data, many areas have been re-classified to a colder zone.
What does this mean for Colorado gardeners? Even if your area has moved up from 5b to warmer 6a, you need to know that any given year, the low temp could still bottom out below the average noted in the zone. So if you start planting 6a plants, put them in protected areas and know that in extremely cold years, there could be winter die back.
We need to pay attention to our zones because they relate to winter hardiness – one of the most critical factors for ongoing plant survival. Still, bear in mind that zone shifts don’t mean that scorching heat, high winds, poor soils, lack of water or an occasional extremely cold winter will go away. All of Colorado’s challenging growing conditions make up our bottom line.
Success in the garden means checking seed packets and nursery catalogs to make sure plants you buy grow in your zone. And, planting in the right exposure, using soil amendments and grouping plants based on similar water requirements are still the name of the game.
Courtesy Associated Landscape Contractors of Colorado and Neils Lunceford, a landscaping company based in Silverthorne that is a member. You may contact them at (970) 468-0340.