The concept of plant hardiness zones provides gardeners and homeowners with a necessary tool for navigating variable climates like those found in Idaho. This standardized geographic reference indicates which perennial plants are most likely to survive the winter in a specific location. The United States Department of Agriculture (USDA) Plant Hardiness Zone Map serves as the definitive reference for this classification, helping individuals make informed decisions about landscape planning.
The Specific Hardiness Zone For Idaho Falls
Based on the most recent 2023 update to the USDA Plant Hardiness Zone Map, the Idaho Falls area is predominantly designated as Zone 5b. This classification is the result of detailed analysis of climate data over a 30-year period, providing a highly specific measure of the region’s winter climate. Gardeners in this area should use Zone 5b as their primary reference point for selecting perennial plantings.
The city’s designation is not uniform across all neighborhoods, as localized geography can cause micro-variations in temperature. Certain areas within the Idaho Falls metropolitan region may register as the slightly colder Zone 5a or the slightly warmer Zone 6a. These differences often correlate with elevation changes or proximity to large water bodies, such as the Snake River, which can moderate temperatures. While 5b is the general zone, consulting a local map by specific zip code can offer the most precise designation for an individual property.
Understanding the Temperature Range
The Hardiness Zone system is built entirely on the average annual extreme minimum winter temperature, which is the single coldest temperature a location is expected to experience each year. The entire classification system is divided into 13 major zones, each representing a 10-degree Fahrenheit range of minimum temperatures. For example, the designation of Zone 5 indicates a range between -20°F and -10°F.
To provide greater accuracy, each 10-degree zone is further split into two 5-degree sub-zones, labeled ‘a’ and ‘b’. Zone 5b, the primary zone for Idaho Falls, specifically represents an average annual minimum winter temperature between -15°F and -10°F. This precise temperature floor determines if a perennial plant will survive the deepest cold snap of the eastern Idaho winter. The 2023 map update incorporated data from more weather stations, allowing for a more granular understanding of these sub-zone differences.
Using the Zone for Successful Planting
The Hardiness Zone designation provides an actionable guide for selecting durable plants that can withstand the cold winters of the Snake River Plain. Gardeners should prioritize buying perennial plants, shrubs, and trees labeled with a hardiness rating that includes Zone 5 or a lower, colder number. For instance, a plant rated for Zones 3 through 7 is considered reliably hardy in Zone 5b.
Choosing a plant rated for a colder zone, such as Zone 4, offers a necessary safety margin against unusually severe winters or unforeseen cold snaps. This practice accounts for the fact that the zone rating is an average and not a guarantee of the absolute minimum temperature in any given year. Gardeners can sometimes successfully push the limits by planting species rated for a slightly warmer zone, like Zone 6.
This “zone pushing” is typically only successful when utilizing microclimates—small areas with unique temperature conditions distinct from the general area. A sheltered spot near a heated foundation, for example, or an area protected from prevailing winter winds can be several degrees warmer than an open yard. Identifying these warmer pockets allows for the cultivation of marginally hardy plants that would otherwise perish during an Idaho Falls winter.