Hardiness of plants is a term used to describe their ability to survive adverse growing conditions. It is usually limited to discussions of climatic adversity. Thus a plant's ability to tolerate cold, heat, drought, or wind are typically considered measurements of hardiness. In temperate latitudes, the term is most often used to describe resistance to cold, or cold-hardiness.

Plants vary a lot in their tolerance of growing conditions. The selection or breeding of varieties capable of withstanding particular climates forms an important part of agriculture and horticulture. Plants can adapt to some extent to changes in climate. Part of the work of nursery growers of plants consists of hardening (or hardening off) their plants, to prepare them for likely conditions in their later life.

Cold-hardiness is generally measured by the lowest temperatures that a plant can withstand. In North America, a set of ten hardiness zones have been defined by the USDA, based on lowest winter temperatures normally reached there.