Artificial Environments. We have pushed the use of plants into totally artificial 

 environments such as expressways, malls, elevated decks, and buildings where plant 

 roots are totally removed from the ground and its warming influence. The assort- 

 ment of plants that can adapt to such environments is proving to be very restricted. 

 Hardiness ratings alone are inadequate to guide landscapers in selecting the most 

 successful plants. 



How the Map The average annual minimum temperature data were analyzed for Mexico, the 

 Was Created United States, and Canada. Of 14,500 stations that measured temperature during 



the period of interest, almost 8,000 could be identified by latitude and longitude and 

 by a valid average annual minimum temperature (i.e., an average based on at least 

 10 years of data). Data from only the latter stations were used in the map. The data 

 were archived by Servicio Meteorologico Nacional (Tucubaya, D.F., Mexico), the 

 National Climatic Data Center (Asheville, NC), and Environment Canada - Cana- 

 dian Climate Centre (Downsville, Ontario). The map is an Albers Equal Area 

 Projection. Standard parallels of 29.5° and 45.5° were used to generate the map of 

 the three countries. The map was computer generated by latitude and longitude. 

 Because of the large area involved, it is not possible to draw one map that is accu- 

 rate for all of North America. The part representing the United States has the least 

 distortion. The Agricultural Research Service proposes to periodically evaluate 

 weather data and issue updated maps as necessary and appropriate. 



This publication is not copyrighted, and permission to reproduce all or any part of it 

 is not required. 



Issued January 1990 



