Effects of shifted temperatures from 15°C to 35°C and back to 15°C on percent germination of selected weed seed species were studied. Cocklebur, common ragweed and pigweed seeds showed a decrease in germination when they were exposed to 15°C; giant ragweed seeds showed an increase in germination when they were exposed to 15°C. Common ragweed and giant ragweed seeds showed an increase in percent germination under all treatments of shifting temperatures. One hundred percent germination in wild mustard seeds was exhibited by an exposure to 15°C. Crotalaria seeds did not exhibit any difference in percent germination on exposure to shifting temperatures.