Montana is known for a short growing season but also micro-climates that make each site unique. Understanding how to assess a property for its unique growing conditions is an important aspect of selecting land for orchard production. Helpful general site selection information can be found on WSU's Tree Fruit website more Montana specific information can be found in MSU's Growing Fruit Trees in Montana guide as well as in the Site Selection and Orchard Design presentation recorded as part of a workshop on Establishing a Montana Orchard.
Additionally, here are some resources that may prove useful in initial evaluation of a site:
Climate, Weather and Terrain
Apples require 8-10 hours of sunlight a day, usually a minimum of 1000 chilling hours and depending on cultivar require at least 100 frost free days to mature. In addition, late frosts at crucial stages of bud development can wipe out a crop. All of these factors are influenced by the climate and terrain of a particular site.
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 available through the Montana Climate Office which visually provide degree day, precipitation and growing season information. 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 more a general assessment of differences on a landscape scale.
To more accurately assess the climate and potential weather challenges of a particular site one must look at the specific site in relation to the surrounding area. Depressions in the landscape or barriers to air movement are locations for potential frost pockets. Narrow valleys and sites situated at the mouths of canyons can also be cooler than surrounding land and often windy. The type of vegetation can also reveal whether the site drains water and receives adequate sun (sage brush, bunch grasses, etc.) or conversely is moist and cool much of the year (moss, ferns, sedges, etc.). If possible observe the potential site throughout the year to determine the ideal location for an orchard based on sunlight, water and air movement.
The NRCS's Web Soil Survey can provide an important first glance at a property's soil resource and basic terrain. It will provide information on soil texture, depth, drainage and water holding capacity among other attributes. This, resource, however is not a substitute for digging soil pits to examine soil depth and changes in texture and soil sampling to gain information about chemical and nutrient composition. Soil tests can easily be obtained using a soil probe (available at most County Extension Offices) and sending the dried sample to a lab for chemical analysis including pH, organic matter, micro and macro nutrients and if desired texture. Depending on the test and laboratory most samples should cost around $25.00 for results with a slight additional charge for recommendations. When choosing a lab consider if the lab specifically tests orchard soils and provides recommendations for apples. They should also be certified. Once a lab is selected they should be contacted directly to get protocols for sampling.
Water and Irrigation Resource
With annual precipitation often below 14 inches, irrigation is a necessity in any Montana orchard. When determining if a site is suitable for your orchard you must consider if there is adequate water to irrigate the trees. Apple trees generally need 20 in (1.7 ac-ft) of water per year, meaning that watering from a well with a 10 ac-ft volume limit will provide enough water for a five acre orchard under normal growing conditions. On properties where a well or irrigation pump exists, an understanding of the available pressure will provide an understanding of what type of irrigation system can be installed. Drip systems can operate at 8-10 psi and sprinklers 10-20 psi, this however does not account for friction loss or change in slope from the water source. Growers should understand their water rights both from irrigation ditches and wells prior to purchasing any property or sizing their orchard. For more information on water rights contact the Montana Department of Natural Resources and Conservation. More information on irrigating orchards in Montana and the west can be found on the orchard irrigation page.
Weeds and unwanted vegetation can be difficult to control. Particularly challenging are perennial weeds such as Canada thistle, quack grass and field bindweed. Even alfalfa can be a competitive foe to young trees. Knowing what weed pressure exists and developing a plan prior to orchard establishment is an important part of assessing a site for orchard suitability. Your county Weed District or Extension Office can be a helpful resource in identifying weeds and other vegetation that might interfere with tree establishment. You can also find resources for identifying mature weeds through the Montana Weed Control Council. The MSU Weed Seedling Identification Guide is an identification resource for growers assessing properties in the spring when many weeds are immature.
Past uses can influence soil quality, the most obvious example being soil disturbance from construction. A less obvious issue is past use of residual herbicides used in pastures where grazing has occurred. Residual herbicides including aminopyralid, aminocyclopyralid, clopyralid and picloram are commonly used in Montana pastures to control noxious weeds. These chemicals provide long-term control of weeds and are not harmful to grazing animals, however, they can persist in soils and animal manures for years. Some signals that further analysis should be conducted to determine if residual herbicides are present include lack of broadleaf plants, a history of the land being used for pasture and grazing and stockpiled manure. If there is any doubt, a bioassay can be conducted to determine if herbicides are present. Bioassays are the preferred form of testing as labratory analysis can cost hundreds of dollars and some plant thresholds for toxicity are below detectable limits for the equipment used. For more information on avoiding residual herbicide contamination and conducting a bioassay refer to MSU's How to Prevent Non-target Injury of Broadleaf Crops and Vegetables by Residual Herbicides.
Keep in mind the micro-climates of Montana's mountainous terrain make any landscape scale tools difficult to apply to a specific area. The best assessments are done on the ground throughout the year to identify issues like frost pockets, pooling water, unwanted vegetation and other attributes influenced by climate, terrain and past uses.