Potassium (K) is a critical nutrient for plant growth and stress resistance. This review highlights the role of K in defending plants against biotic and abiotic stresses, including diseases, pests, drought, salinity, cold, frost, and waterlogging. K influences plant growth, anatomy, morphology, and metabolism, and plays a key role in physiological and molecular mechanisms that enhance plant resistance. The availability of K and its effects on plant stress resistance are discussed, along with the potential for improving plant resistance through modified K fertilizer inputs and the selection of appropriate plant species or varieties. K is essential for enzyme activation, protein synthesis, photosynthesis, osmoregulation, stomatal movement, energy transfer, phloem transport, cation-anion balance, and stress resistance. In biotic stress, K deficiency increases susceptibility to pests and diseases, while adequate K levels reduce disease incidence and pest damage. K enhances plant resistance by improving cell wall strength, stomatal function, and the synthesis of defensive compounds. In abiotic stress, K plays a crucial role in drought resistance by improving root growth, water uptake, and maintaining cell membrane stability. K also helps in osmotic adjustment, which is essential for maintaining turgor pressure and water retention under drought conditions. K is involved in stomatal regulation, which is critical for water conservation during drought. Additionally, K helps in detoxifying reactive oxygen species (ROS) produced under stress conditions, reducing oxidative damage. In salt stress, K helps in maintaining a high K+/Na+ ratio, which is essential for salt tolerance. K deficiency leads to increased Na+ uptake and toxicity, reducing plant growth and salt tolerance. K improves salt tolerance by enhancing K+ uptake and reducing Na+ accumulation. In low-temperature stress, K enhances plant survival by improving antioxidant levels and reducing ROS production. K also helps in maintaining membrane stability and osmotic adjustment, which are crucial for cold tolerance. In waterlogging stress, K helps in maintaining oxygen supply to roots and reducing oxidative damage. K improves plant growth, photosynthetic capacity, and nutrient uptake under waterlogged conditions. Overall, maintaining an optimal K nutritional status is essential for plant resistance to various stresses. Future research should focus on understanding the molecular mechanisms of K in plant stress resistance, the role of K in different plant tissues and organs, and the interaction of K with other nutrients in different agroecological systems. This knowledge is crucial for improving crop production and sustainability in the face of increasing environmental challenges.Potassium (K) is a critical nutrient for plant growth and stress resistance. This review highlights the role of K in defending plants against biotic and abiotic stresses, including diseases, pests, drought, salinity, cold, frost, and waterlogging. K influences plant growth, anatomy, morphology, and metabolism, and plays a key role in physiological and molecular mechanisms that enhance plant resistance. The availability of K and its effects on plant stress resistance are discussed, along with the potential for improving plant resistance through modified K fertilizer inputs and the selection of appropriate plant species or varieties. K is essential for enzyme activation, protein synthesis, photosynthesis, osmoregulation, stomatal movement, energy transfer, phloem transport, cation-anion balance, and stress resistance. In biotic stress, K deficiency increases susceptibility to pests and diseases, while adequate K levels reduce disease incidence and pest damage. K enhances plant resistance by improving cell wall strength, stomatal function, and the synthesis of defensive compounds. In abiotic stress, K plays a crucial role in drought resistance by improving root growth, water uptake, and maintaining cell membrane stability. K also helps in osmotic adjustment, which is essential for maintaining turgor pressure and water retention under drought conditions. K is involved in stomatal regulation, which is critical for water conservation during drought. Additionally, K helps in detoxifying reactive oxygen species (ROS) produced under stress conditions, reducing oxidative damage. In salt stress, K helps in maintaining a high K+/Na+ ratio, which is essential for salt tolerance. K deficiency leads to increased Na+ uptake and toxicity, reducing plant growth and salt tolerance. K improves salt tolerance by enhancing K+ uptake and reducing Na+ accumulation. In low-temperature stress, K enhances plant survival by improving antioxidant levels and reducing ROS production. K also helps in maintaining membrane stability and osmotic adjustment, which are crucial for cold tolerance. In waterlogging stress, K helps in maintaining oxygen supply to roots and reducing oxidative damage. K improves plant growth, photosynthetic capacity, and nutrient uptake under waterlogged conditions. Overall, maintaining an optimal K nutritional status is essential for plant resistance to various stresses. Future research should focus on understanding the molecular mechanisms of K in plant stress resistance, the role of K in different plant tissues and organs, and the interaction of K with other nutrients in different agroecological systems. This knowledge is crucial for improving crop production and sustainability in the face of increasing environmental challenges.