The Major Problem with the USDA Zone Map

The Major Problem
 with the
 USDA Zone Map

The USDA Zone Map is undoubtedly a great tool
 to rate hardiness for landscaping plants. 
However this map is ONLY the AVERAGE
 coldest temperature, not the coldest temperature
 that is possible. In fact, with a very unstable
 climate (likely due to climate change) colder
 or warmer winters are far more likely. In fact
 there have been at least 2 winters in Indiana 
in the past 10 years alone that have seen temps 
colder than the zone I am in. I am in
 Indianapolis, IN. In the Winter of 2014 the temp
 dipped down to -15°F in Indianapolis, and
 -20°F to -25°F on the north side where I live. 
Indianapolis had a zone 5b winter in a zone 6a,
 I had a zone 4b/5a winter in a 5b/6a location. 
In 2019 I had a zone 5b winter and I am 
technically 6a bordering zone 5b. It is ALWAYS
 best to go with the colder side rather than
 warmer side due to this very reason.
 Indianapolis is technically zone 6a, in reality
 it is a solid zone 5. Southern Indiana is a solid
 zone 6 (which fits the current map). 
But Indianapolis area northward is a solid
 zone 5, Bloomington area south is a solid
 zone 6 (this fits the d 1990 map). The map
 really should be updated more than every 
20 years especially with a rapidly changing climate.
 Virtually the entire country moved up (warmer)
 a whole USDA Zone from 1990 to 2012 
(most recent). With my own experience
 the modern map is not correct in many 
locations. Indianapolis should have remained
 a zone 5 in the 2012 map. Only minor or
 perhaps no changes at all should have been
 made with the new map for Indiana. The climate
 is changing, but parts of the world are getting
 colder as the climate is disrupted from CO2 
emissions, as a result we have had colder winters
 than the map says we can have. I have had weather
 colder than the map says and reached the minimum 
temps at least 4 times in 10 years really says something to me. 

•

When landscaping please take this into consideration, 
and go a zone or at least a half a zone (5°F) colder. 
If you are a zone 6a, Do not use zone 6 and warmer 
plants unless it is protected and you or your customer are
 aware and are willing to take the risk.

•

Sum up: The 1990 map still is more realistic than the 2012
 (current) map which is too warm for lots or perhaps the whole country.