Cici, S. Z. H. and Van Acker, R. C. 2011. Relative freezing tolerance of facultative winter annual weeds. Can. J. Plant Sci. 91: 759-763. To understand why some of the facultative winter annual weeds are more abundant in spring rather than both in fall and spring, we assessed the freezing tolerance and re-growth capacity of 12 species collected across Canada. Our study allowed us to classify these species in three broad categories based on their relative tolerance to freezing temperatures. Freezing scores and biomass reproduction after freezing were generally consistent with field observations. It was shown that early emergence of weeds in spring is not, however, systematically related to superior freezing tolerance.