Early Frost

Photo 1: Cortland apples potentially damaged by sudden changes in temperature and early frosts (October 2019). Photo credit: Katrina Mendrey.

Montana's climate varies both on a macro and micro scale, making any crops including apples vulnerable to weather extremes in all seasons. Following is a summary of the various constraints Montana's climate and weather can place on growing apples in the region.

Overall Growing Conditions

Montana has a short growing season with much of the state having only 135 or less frost free days on average. Water too can be a constraint as Montana's precipitation in growing areas is often less than 14" requiring irrigation to grow a successful apple crop. The climate of a site can be evaluated on a macro scale by locating the nearest Agrimet station and reviewing historical weather data to get an idea of max/min temperature, precipitation, occurrence and timing of late season frosts and other weather related information influencing plant growth and development. In addition, there are maps which visually provide degree day, precipitation and growing season information available through the Montana Climate Office. These tools, however, should not be the primary factor in deciding if a location is suitable, as they are not accurate to a finite area but offer a more general assessment of differences on a landscape scale.  

Microscale Evaluation

Any site should be evaluated more closely prior to planting to understand the microclimate of the particular landscape. Special attention should be given to frost pockets, sun exposure and prevailing winds for a particular location. More information on site evaluation can be found on the Site Selection page of this guide.

Sudden Changes in Temperature

Much of the Intermountain West experiences sudden changes in diurnal temperature which can exceed 40F. These shifts in temperature can be even greater from day to day with sudden freezing temperatures especially in crucial shoulder seasons. This can be hard on plants as they are breaking and going into dormancy, leaving trees vulnerable to frost damage and winter injury. Photo 1 above provides an example of how an early and fast frost can damage trees before they are fully dormant, scorching leaves, damaging new growth and potentially killing young trees.  

Extreme Weather

Another factor in growing apples in the Intermountain West is the onset of extreme weather throughout the growing season. Hail and strong winds can damage crops and permanently injur trees, especially young ones which can be girdled by hail damage or broken at the graft by strong winds. Understanding the risk of such events on your particular site can help you better prepare for them and protect your trees from injury when possible. Options might include staking or trellising trees, choosing larger rootstocks, and on a small scale using netting to protect trees from hail damage.

Snow Cover

Snow cover through the winter can protect trees roots from extremely low temperatures, but can also lead to  sunscald and increased rodent damage on unprotected trees. Snow provides protection and habitat for voles capable of girdling trees by feeding on bark. Additionally, extremely high snow cover can burry the fencing and tree wraps in place to protect trees from feeding by rabits and other herbivores.  Sun reflecting off of snow can also warm trees cells leaving them susceptible to cold injury when temperatures drop at night. For more information on protecting trees from wildlife and sunscald visit the Early Tree Care section of this guide.