Technical Abstract: The objective of this study was to further define the environmental requirements for safesites for germination of seeds (achenes) of diffuse knapweed (Centaurea diffusa Lam.). Germination temperature profiles were developed for diffuse knapweed seeds collected from sites in the Great Basin and Colorado. Each profile consisted of achenes germinated at 55 constant or alternating temperatures from 0 through 40oC. The resulting germination was used to develop quadratic response surfaces with regression analysis. Some germination occurred from 71 to 96% of the temperature regimes depending on the accession being tested. Maximum observed germination ranged from 85 to 98%. Optimum germination, defined as the maximum observed minus one half the confidence interval at the 0.01 level of probability, occurred at a wide range of temperatures from cold periods of 0 through 20oC alternating with warm periods of 10 through 35oC.