Iris frost resistance

Frost resistance of irises is a qualitative indicator determined through phenological observations following overwintering. For bearded iris varieties, the critical temperature threshold at which flower buds sustain damage ranges from –12°C to –14°C; however, for the least resistant varieties, this can rise to –7°C. Under conditions of critical frost and the absence of snow cover, rhizome death and freezing of their upper parts are possible.

Agrotechnical factors directly affect plant resistance. Excessive application of organic fertilizers leads to succulent growth, increasing tissue water content and reducing frost resistance. An important condition for plant preservation is selecting sites with effective drainage, as stagnant moisture combined with temperature fluctuations triggers the development of bacterial rot. For less winter-hardy groups, such as Japanese irises, the use of air-dry shelters is necessary.