Grass Species And Varieties For Severe Winter Climates (P3)
Winter stress tolerance
There are several reasons why grass plants are injured or killed during the winter. Details about this are presented in other factsheets, but the different stresses can make it difficult to rank turf grass species and varieties according to the general term winter stress tolerance. Some species do, for instance, tolerate low freezing temperatures, but are severely attacked by snow mould. In most species there is a positive correlation between the ability to resist freezing, desiccation and ice encasement and the presence of winter-active fungi.
Winter stress tolerance is closely related to the acclimation status of the plant. When a grass plant is well acclimated and prepared for the winter, it has stop ped growing, some extra sugar has been stored for the winter, anti-freeze proteins have been produced inside the cells, and the cell membranes have been changed for improved stability under freezing and thawing conditions.
This acclimation status of the plant depends on environmental factors. The most important signal is temperature. A period of low temperatures in autumn will induce winter acclimation. Warm spells during the winter can de-acclimate the turf. The turf grass species vary in how sensitive they are to these warm periods.
The following ranking of grass species is first and foremost based on the evaluation of species and varieties at Nordic locations over the last 15 years. The test programs include both coastal and inland climates at latitudes between 56 and 65 °N. Results about turf grass species are summarized in The Nordic Turfgrass Guide.
Some STERF research projects have also added specific knowledge about the species’ freezing tolerance and ability to survive under different maintenance and climatic conditions.