New Plant Hardiness Zone Map in 2012

This has certainly been an unusually warm winter so far. Many people are concerned that the warm temperatures will results in plants sprouting too soon or in heavy summer insect problems.

Some people wonder if our climate is changing due to various factors, including global warming.

Source: Illinois State Climatologist  

The USDA released their new Plant Hardiness Zone map recently. The 2012 changes show that we are indeed experiencing overall warmer winter temperatures.

The USDA hardiness zones are based on average winter minimum temperatures. According to Jim Angel, Illinois State Climatologist at the Illinois State Water Survey, “This is certainly an improvement on the old USDA map that was based on data from a relatively short and cold period from 1974 to 1986.” Angel says that the new map is based on a longer period that includes the milder winters of the 1990s and early 2000s.

The new map can be found at http://planthardiness.ars.usda.gov.

To reflect these milder winters, most zones have shifted northward. Angel says, “Here in Champaign I used to be in the middle of Zone 5 according to the old USDA map. Now I'm almost in Zone 6.”

These maps are a useful guide. Most garden catalogs list the hardiness zone rating for their plants. The hardiness zone is an important plant selection guide, but it is only one factor in determining if a plant will survive the winter. Other factors, such as moisture levels and critters (voles, rabbits, and mice), also affect a plants chance of winter survival.

Speaking of critters, will this mild winter affect insect populations this summer? According to Phil Nixon, Extension Entomologist, mild winters or cold winters have little effect on the number of insects that people typically notice.

Nixon says that it is true that in a mild winter, more pest insects survive, but so do more predatory insects, parasitic insects, and other natural enemies. Contrary to popular belief, Nixon says that the most important impact on insect numbers is spring weather. Cool, damp springs encourage the development of fungi that attack insects and slow the development of insects. The result is fewer caterpillars and other insects surviving through the spring.

And finally, if you have daffodils sprouting or plants leafing out early, don’t fret. Although some of the early growth could experience freeze damage later, the plants should be fine overall once our official spring finally arrives. You can add a layer of mulch over the sprouting plants to provide additional winter protection, but it is probably not essential.

Published in Canton Daily Ledger Column 2-4-2012