Nebraska rises in plant hardiness zones
NEBRASKA CITY – Justin Evertson of the Nebraska Forest Service says the northward expansion of plant hardiness zones is a 30-year trend for warmer winters, but is only one factor that decides plant survivability.
He said an array of Nebraska’s native plants, grasses and trees have adapted to timely rainfalls, drought and summer heat, but a problem for new plants is often the temperature fluctuations of the Great Plains.
Evertson: “The biggest problem for killing plants happens as they are waking up in April because the sap starts flowing and they are vulnerable to real quick temperature freezes. So, it’s a 30 or 25 degree freeze in April that kills the plants, not the 30 degrees below in February.”
The plant hardiness zone that covered most of Kansas the past 30 years has now moved north to include southern and portions of eastern Nebraska from Falls City to Omaha. The zone change shows that the area is about 2.5 degrees warmer than the 2012 map. There are also micro climates on sunny southward slopes and at the bottoms of hills. An area from Marysville, Mo., to Omaha has gone from mostly 5a to 6a zones to now mostly 6a to 7a.
Evertson said the map provides a good rule of thumb when looking for unusual plants to try.
Evertson: “There are a lot of plants that are right on the edge of being adaptable to Nebraska. For example, there is Southern Magnolia, which can be grown in the Kansas City area without too much trouble. Bring it up just a little further to Nebraska, it doesn’t want to grow here. But there are one or two living examples now in Brownville and the Falls City area.”
He said sweet gum, a North American native tree, is growing at the University of Nebraska-Lincoln campus, but growing the species would not have even been attempted 30 years ago.
The warmer temperatures are a detriment to other trees like the Colorado blue spruce, which does not thrive under the hot temperatures of Nebraska’s summer nights.
Evertson: “Survival verses thriving is a good way to think about it. So, if you’re picking plants that are zone 6a for Nebraska, you might get some of them to work some of the years, but the chance for those plants to thrive is reduced. You would still want to pick plants from zones 4b to 5b probably.”
He said lacebark elm is another tree that has experienced winter die back in Nebraska, but now the tree is surviving the winter. Herbs like lavender and rosemary and trees like crape myrtle are also more likely to thrive with the warmer winters.