USDA PLANT
HARDINESS MAP
For your convenience, we have reproduced the new United States Department of Agriculture’s (USDA) Plant Hardiness Map. The hardiness zones are based on the average annual low temperature for each zone. Many factors, such as altitude, snow cover, degree of exposure to wind, proximity to bodies of water, excessive or minimal rainfall, soil types, etc. can create variations within zones. Please understand that these conditions can adversely affect your wildflowers. Therefore, the recommended spring and fall planting dates for Iowa mentioned on this site should be used only as a general guide.
ZONE 1 BELOW -50F Sow seed in early spring when soil can be worked
ZONE 2 -50F to -40F Sow seed in early spring when soil can be worked
ZONE 3 -40F to -30F Spring: April 15-June 15 -- Fall: August 15-October 1
ZONE 4 -30F to -20F Spring: April 15-June 15 -- Fall: September 1-October 15
ZONE 5 -20F to -10F Spring: April 15-June 15 -- Fall: September 1-October 15
ZONE 6 -10F to 0F Spring: March 15-May 15 -- Fall: September 15-November 1
ZONE 7 0F to 10F Spring: February 15-April 15 -- Fall: September 15-November 15
ZONE 8 10F to 20F Spring: January 15-March 1 -- Fall: October 1-December 1
ZONE 9 20F to 30F Spring: January 1-March 1 -- Fall: October 1-December 1
ZONE 10 30F to 40F Spring: January 1-March 1 -- Fall: October 1-December 1
ZONE 11 ABOVE 40F Spring: January 1-March 1 -- Fall: October 1-December 1
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