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Grapes are highly susceptible to cold damage during critical developmental stages, impacting viticulture. Understanding the intricate dynamics of cold hardiness in grape dormant buds and phloem tissue is crucial for developing effective mitigation strategies. In this study, we investigated the LT50values, representing the temperature at which 50% of buds are damaged, under different treatments and sampling times. In our research, we evaluated the effects of four treatments—potassium oxide (K2O), calcium chloride (CaCl2), seaweed (SW), and a control—on the cold hardiness of grapevine buds and phloem tissue. Primary bud LT50values varied across seasons, with January at −22.46 °C, February at −22.35 °C, and March at −20.45 °C. K2O treatment showed a trend toward improvement, although the difference from the control (−21.99 °C) was not statistically significant. Regarding LT50values, CaCl2and SW applications did not significantly differ from the control. Tertiary buds, however, exhibited a substantial enhancement in cold hardiness with K2O application, displaying significantly lower LT50values compared to the control (−23.55 °C). Phloem tissue LT50values did not significantly differ among treatments, showing less variability. Bud water content significantly increased with K2O application in all sampling periods (January: 35.41% vs. 35.61%; February: 34.03% vs. 39.16%; March: 42.40% vs. 37.82%), while shoot water content remained stable. In conclusion, K2O emerges as a key influencer, particularly in enhancing the cold hardiness of tertiary buds. These insights contribute to the knowledge base for targeted frost mitigation strategies in viticulture.