Lesquerella (Lesquerella fendleri) is a potential alternative crop that is being studied for commercial oilseed production. Understanding the minimum temperatures for germination and seedling growth is important for determining potential areas for lesquerella production. The objectives of this study were to determine the cardinal temperatures for germination and seedling growth, and to screen ecotypes for germination and growth characteristics. A temperature gradient table arrangement was used to observe seed germination over a range of temperatures, and time to germination and shoot appearance. Times to 5 mm root length and 5 mm shoot length were also measured to assess cardinal temperatures for seedling survival and growth. Two different species were examined, L. fendleri and a species we refer to as ‘L. pallida aff.’ because it differed from typical L. pallida plants in chromosome number and in oil quality. We concluded that both germination and growth of L. pallida aff. occurred fastest at 22 ◦ C, whereas L. fendleri germinated earlier at 18 ◦ C, but grew faster at 22 ◦ C. L. pallida aff. also had lower germination than L. fendleri over the range studied. Non-dormant seeds of improved lines of L. fendleri had better performance at temperatures above 22 ◦ C than did unimproved accessions. Lines of L. fendleri selected for high oil content and salt tolerance had similar temperature requirements for germination except for improved line WCL-LO3, the current line being used in production. This line had optimal temperatures 6 ◦ C higher for germination and growth than the other improved lines. Accessions of L. fendleri collected from elevations above 2000 m performed better at warmer temperatures, whereas those collected from elevations below 2000 m tended to perform better at cooler temperatures. Dormant seeds of L. fendleri germinated more quickly at low temperatures and had lower base ( 7 ◦ C and 28 ◦ C, respectively). We speculate that this partial dormancy trait allows populations of L. fendleri to exploit a wider range of temperature conditions in the wild in order to thrive in extreme environments.