Planting Zone 1a: Plants That Grow in USDA Hardiness Zone 1a

USDA hardiness zone 1a covers areas where the coldest winter night averages −60 °F to −55 °F (−51.1 °C to −48.3 °C). Zone 1a doesn't occur in the contiguous United States; it is found in Alaska. PlantoScan lists 1 plant that survives winter outdoors in zone 1a.

Winter low (°F)
−60 °F to −55 °F
Winter low (°C)
−51.1 °C to −48.3 °C
US ZIP codes
—
Hardy plants
1

What Temperatures Define Hardiness Zone 1a?

Hardiness zone 1a is defined by an average annual extreme minimum temperature of −60 °F to −55 °F (−51.1 °C to −48.3 °C). This is the colder half of zone 1, which spans −60 °F to −50 °F in total.

The value is a 30-year average of each winter's single coldest night, taken from 1991–2020 weather records for the 2023 USDA map. Individual winters regularly run a few degrees colder, so plants rated exactly to zone 1abenefit from mulch and a sheltered spot. Gardeners who don't know their zone yet can look up their USDA hardiness zone by ZIP code before comparing plants.

Warmer: zone 1b (−55 °F to −50 °F) →

Which States Are in Hardiness Zone 1a?

Zone 1a doesn't occur in the contiguous United States. On the 2023 USDA map it is found in Alaska, which the USDA ZIP code table doesn't cover.

What Plants Grow in Zone 1a?

1 plant in PlantoScan's catalogue is hardy in zone 1a, meaning zone 1a falls inside its hardiness range.

Trees for Zone 1a (1)

Which Popular Plants Aren't Hardy in Zone 1a?

These popular plants need a warmer zone than 1a to survive winter outdoors. Grow them as houseplants, in containers that move indoors before the first frost, or as annuals replanted each spring.

How Do You Garden Successfully in Zone 1a?

Successful zone 1a gardens rely on perennials, shrubs and trees rated to zone 1 or colder. Plants rated right at zone 1a survive typical winters but benefit from mulch, windbreaks and a spot near a warm wall.

A hardiness zone describes winter cold only. Planting dates follow your local last spring frost and first fall frost, which differ by weeks within zone 1a — a last frost date calculator by ZIP code gives the dates for your garden. Summer heat, rainfall and soil drainage decide whether a hardy plant thrives. Microclimates matter as well: raised beds, slopes and paved areas warm up faster, while low ground collects cold air on still nights.

Zone temperatures and ZIP codes: 2023 USDA Plant Hardiness Zone Map, USDA Agricultural Research Service and the PRISM Climate Group, Oregon State University. Plant hardiness ranges come from PlantoScan's plant database and are estimates — local conditions, cultivars and winter protection change what survives.