Field margins in agricultural landscapes exhibit considerable structural variation, ranging from herbaceous strips to shrubby borders and tree-rich hedgerows, which can influence microclimatic conditions and wildlife habitat quality. Despite their ecological importance, the microclimatic properties of these diverse field margins remain poorly characterized. By generating fine-scale thermal heterogeneity, field margins may act as microrefugia, buffering organisms against temperature extremes and supporting climate adaptation. We investigated how local vegetation structure and landscape context influence microclimatic variation in a temperate Canadian agricultural landscape. From June to September 2018, we deployed 180 temperature data sensors across 30 fields in 20 1-km2 landscapes in eastern Ontario, Canada, recording conditions in both field margins and adjacent crop fields. We quantified daily maximum and minimum temperature offsets between margins and fields, compared these to regional weather station data, and assessed the sensitivity of measurements to solar radiation shielding. Linear mixed-effects models showed that tree-rich margins strongly reduced maximum temperatures and elevated minimum temperatures, while herbaceous and shrubby margins resulted in limited thermal buffering. Margin width and landscape-level natural vegetation cover had no detectable effects. Local microclimate measurements were consistently more extreme than regional weather data, highlighting the importance of fine-scale monitoring. Although radiation shielding reduced the magnitude of temperature offsets, the overall direction of effects remained consistent. Our findings underscore the ecological value of conserving and expanding treed field margins, which can provide microrefugia and enhance wildlife resilience under climate change.