Idaho Plant Hardiness Zones Map And Gardening Guide

Summary

Idaho’s plant hardiness zones include 3b through 7b. Across these zones, the average minimum extreme winter temperature ranges from -35°F (-37.2°C) to 10°F (-12.2°C).

Idaho’s climate ranges from continental to semi-arid. The former has warm summers and cold winters. The latter is often sunny and gets less precipitation.

Idaho’s growing season is shorter. Choose the right plants, extend your growing season, practice water-wise gardening, practice soil care, and consult with local professionals. Also, prepare for extreme weather events such as blizzards, thunderstorms, and flash floods.

Plant suggestions include but aren’t limited to:

Western White Pine
Bitterbrush
Silvery Lupine
Asparagus
Chives
Juniper Berry
Huckleberry
Chinese Stonecrop

Idaho Plant Hardiness Zones^8,9

USDA Hardiness Zone	Average Minimum Extreme Winter Temperature Range Fahrenheit (°F)Celsius (°C)	Average Last Frost Date Range In Spring (Beginning Of The Growing Season)	Average First Frost Date Range In Autumn (End Of The Growing Season)
3b	-35°F to -30°F -37.2°C to -34.4°C	Late May to early June	Early September
4a	-30°F to -25°F -34.4°C to -31.7°C	Late May to early June	Early to mid-September
4b	-25°F to -20°F -31.7°C to -28.9°C	Late May	Early to mid-September
5a	-20°F to -15°F -28.9°C to -26.1°C	Mid to late May	Mid to late September
5b	-15°F to -10°F -26.1°C to -23.3°C	Mid to late May	Mid to late September
6a	-10°F to -5°F -23.3°C to -20.6°C	Mid to late May	Mid to late September
6b	-5°F to 0°F -20.6°C to -17.8°C	Mid to late May	Mid to late September
7a	0°F to 5°F -17.8°C to -15°C	Early to mid-May	Late September to early October
7b	5°F to 10°F -15°C to -12.2°C	Late April to early May	Late September to early October

^{Sources: 8-9}

Idaho’s Growing Conditions

Map showing Koppen climate types in Idaho.

_{Credit to Wikipedia}

General Climate^1,4-6

Idaho has a variety of continental climates as well as semi-arid regions. Three distinct growing areas exist in Idaho:

Northern Idaho
Eastern and Central Idaho
Southwestern Idaho

The mountains of the state create various climate patterns that are, generally speaking, affected by elevation. Typically, as elevation increases, temperature drops, and precipitation increases.

Northern Idaho has a continental climate and falls within the cooler temperature ranges in the state. Frost dates vary significantly based on elevation.

Southwestern Idaho is warmer and has a longer growing season. The climate is semi-arid. Though the area experiences all four seasons, it is often sunny. Mountains flank the area on all sides, so it receives less precipitation than other areas.

Eastern and Central Idaho have continental climates. This means they have warm summers and cold winters and the growing season is short, varying based on elevation. Gardening in this part of Idaho can be more challenging.

Microclimates

USDA plant hardiness zones are an important starting point for your garden, but you’ll also need to consider microclimates.

Microclimates are areas where specific conditions create a climate different from the climate they’re situated in.

Buildings, fences, paved areas, or short hills and valleys can create these microclimates.

They can be as small as a space in your backyard or as large as a city.

In other words, learn about your local conditions from local experts to see if your garden falls into a microclimate.

Extreme Weather

Blizzards

Blizzards are winter snowstorms with strong winds and intense snowfall over several hours. They limit visibility and can leave behind large amounts of snow.

These elements and the freezing temperatures present a risk of damage to your plants.

To prevent what is known as “winter kill” (exactly what it sounds like), select and plant varieties that can withstand cold temperatures.

You likely won’t have problems in your garden as a result of snow.

To prepare your plants for winter, wrap them with burlap, water deeply, and cover their roots with a layer of straw or wood chip mulch before temperatures drop below freezing. You don’t have to do all of these, but each helps in its own way.

If you have any amount of snow, pile it over top of growing beds. As it melts, your soil absorbs the moisture.

If you have one, you can also fill your rain barrel with snow and use the water from there later.

Thunderstorms

Several regions throughout Idaho experience powerful thunderstorms. These storms include strong, damaging winds, thunder, lightning, and pronounced rain that can create floods.

As such, it’s a good idea to determine the prevailing winds in your area and locate growing beds in places that afford your plants some protection or shelter. These may be next to existing structures or windbreaks.

Staking and supporting plants also help protect against wind damage to some extent. You can also attach sheets or floating row cover to stakes, trellises, and planting cages. Doing so will help provide some protection in the event of storms.

Flash Floods

Though flooding is not particularly frequent in Idaho, flash floods do sometimes occur in its mountainous regions.

Large amounts of rain cause flooding, especially as they cause watercourses such as rivers and streams to overflow.

When water has no immediate place to drain, it can create extensive damage, resulting in landslides.

Appropriately grade and slope your garden to improve drainage. This is the best course of preventative treatment to help manage this risk.

Growing Season⁷

Idaho’s growing season is relatively short, though this can vary based on altitude. Temperatures can vary significantly between day and night throughout the state. Choose plants acclimated to these fluctuations.

Use USDA data and recommendations as starting points. Remain aware of current weather conditions. This will allow you to adapt to yearly variations appropriately.

Idaho Gardening Tips

Yellow Flowers In Field With Sawtooth Mountains In Background - Idaho

Choose The Right Plants

In Idaho, you must contend with various conditions, such as arid conditions, sometimes poor soils, quickly changing temperatures, and a relatively short growing season. Plants raised to withstand the challenges specific to the conditions of Idaho have the best chance of surviving.

Extend Your Growing Season

Since Idaho’s growing season is on the shorter end, growing plants with lengthy growing times means starting seeds indoors and transplanting seedlings to your garden once temperatures have warmed.

To extend the season in the autumn and protect your plants from frost damage, use sheets, floating row cover, frost cloth, cloches, hoop houses, or even cold frames and greenhouses to maintain temperatures good for growing for a few days, weeks, or months more.

Practice Water-Wise Gardening

Maximize your available water resources if you’re in one of Idaho’s arid growing regions.

Install rain barrels or other water catchment systems to capture precipitation. You can also install drip irrigation systems to facilitate growth even through droughts.

Choosing to grow drought-tolerant plants is also helpful.

How and when you water your plants also affects your water efficiency. Water low to the ground, underneath plant foliage, to avoid splash up and potential transmission of disease from the soil. Watering early in the day before the heat has accumulated mitigates the evaporation risk.

Deep watering once a week is better for your plants than little bits of moisture here and there. Doing so allows water to permeate deeper and remain in the soil (and available to your plants) longer.

Practice Soil Care

Improving soil structure through the addition of organic materials such as compost, straw, grass clippings, or wood chips benefits your garden in the following ways:

Improving soil quality as it breaks down
Retaining water in the soil
Suppressing weeds
Insulating roots from extreme temperatures
Inviting healthy garden predators to keep pest populations down

Idaho soil can be sandy. This means water and nutrients will simply pass through the soil. Adding organic material such as decomposing leaves, grass clippings, straw, or finished compost will improve the soil.

Consult With Local Professionals

Consulting with local gardening professionals allows you to benefit from their experience with your area’s conditions, the plants that do well there, and overall best practices.

Idaho Plant Suggestions^2,3

Trees

Western White Pine (Pinus monticola)
Bigtooth Maple (Acer grandidentatum)
Western Larch (Larix occidentalis)

Shrubs

Bitterbrush (Purshia tridentata)
Wild Mock Orange (Philadelphus lewisii)
Sagebrush (Artemesia tridentata)

Flowers

Silvery Lupine (Lupinus argenteus)
Common Camas (Camassia quamash)
Arrowleaf Balsamroot (Balsamorhiza sagittata)

Vegetables

Asparagus (Asparagus officinalis)
Beets (Beta vulgaris)
Potatoes (Solanum tuberosum)

Herbs

Chives (Allium schoenoprasum)
Thyme (Thymus vulgaris)
Spearmint (Mentha spicata)

Spices

Juniper Berry (Juniperus communis)
Caraway seeds (Carum carvi)
Catmint (Nepeta cataria)

Fruits

Huckleberry (Vaccinium spp.)
Elderberry (Sambucus spp.)
Apples (Malus domestica ‘Gala’)

Succulents

Chinese Stonecrop (Sedum tetractinum)
Shrubby Ice Plant (Ruschia pulvinaris)
Ruby Mantle Sedum (Sedum spurium ‘Ruby Mantle’)

Disclaimer

Any of the above can change and is not exhaustive.

Treat anything above like a good starter guide. Then use that as a foundation as you consult with local gardeners, professionals, forecasts, guides, and organizations.