Despite advances in restoration of degraded lands around the world, native plants are still underutilized. Selection of appropriate plant materials is a critical factor in determining plant establishment and persistence. To better inform decision-making, we examined cold-hardiness dynamics, flowering phenology, and survival among five geographically distinct sulfur-flower buckwheat (Polygonaceae: Eriogonum umbellatum Torr.) populations in a common garden. LT50 (a measure of freezing injury) was determined every 6 weeks across a complete year; one population was also evaluated at the source. Cold-hardiness dynamics were similar across populations, with annual fluctuations in mean LT50 exceeding 40°C. Rate of deacclimation (i.e. loss of cold tolerance) in spring varied across populations and was not related to the elevation from which a population came. Plants were less cold hardy in October 2014 compared to October 2013, likely reflecting a response to colder local conditions in 2013. Although the range of LT50 was similar for a single comparison of common garden versus wild-grown plants, wild-grown plants acclimated and deacclimated earlier than common garden-grown plants. Plants derived from a low-elevation population showed delayed flowering phenology, while high-elevation populations showed earlier flowering phenology, with one high-elevation population having the lowest survival rate in the common garden. These results suggest that while considerable plasticity in seasonal cold-hardiness dynamics occur, population variability in deacclimation and flowering phenology have implications for selection and movement of sulfur-flower buckwheat for ecological restoration.