Zone 5a: What Grows and How to Garden There

What a zone 5a winter means

Zone 5a is the colder half of zone 5, and its winters decide much of what you can grow. Most of the work happens at planting time: choose perennials, shrubs and trees rated to zone 5 or colder, and give anything at the edge of its range a sheltered spot. Wisconsin Extension’s advice applies here: if you are unsure whether your garden behaves like the “a” or the “b” half of a zone, pick plants hardy to the colder half.

Snow helps. Snow cover insulates the soil, and Illinois Extension notes that forsythia flower buds buried under snow survive cold that kills the buds above the snow line. Open, windswept sites with no snow are harder on plants than sheltered ones.

Where zone 5a is

Zone 5a takes in southern Minnesota around the Twin Cities, northern Iowa, central Wisconsin, eastern South Dakota and parts of Nebraska, along with upland areas of upstate New York, Vermont, New Hampshire, Maine and Michigan. In the West it covers mountain valleys and high plains in Montana, Wyoming, Colorado, Idaho, Utah, Nevada and New Mexico, and in Alaska the Anchorage area.

Fruit trees and small fruit

Apples and pears are the backbone of the zone 5a orchard: Virginia Tech gives their buds hardiness to about -25°F.

Tart cherries are hardier than sweet. Iowa State finds the University of Minnesota cultivars ‘Northstar’ and ‘Meteor’ the best performers, with excellent cold hardiness.

Plums: skip Japanese plums, which Iowa State calls not reliably hardy. European ‘Mount Royal’ grows statewide in Iowa, and hybrid plums such as ‘Alderman’, ‘Pipestone’, ‘Superior’ and ‘Underwood’ are hardy statewide but need a pollinator such as ‘Toka’.

Peaches are the gamble. Flower buds die from about -10°F, losing roughly another 10% for each degree colder (Illinois), and Iowa State reports buds destroyed below -18°F and trees damaged at -25°F.

Perennials, bulbs and shrubs

Perennials hardy to zone 3 or 4 are safe choices: hostas, daylilies, purple coneflower, peonies and lilies all fit. Tulips are hardy to zone 3 and daffodils to zone 4, so spring bulbs planted in fall come back reliably.

For shrubs, smooth and panicle hydrangeas bloom on new wood and flower every year, while bigleaf hydrangea often winter-kills to the ground (Cornell). Among azaleas and rhododendrons, Nebraska Extension points to the Northern Lights azaleas, with flower buds hardy to -30 to -40°F, and ‘PJM’ rhododendron to -30°F; give them morning sun and afternoon shade out of winter wind.

Special concerns

• Herbs that don’t overwinter. Rosemary will not survive outdoors; grow it in a pot and bring it in. English lavender (‘Munstead’, ‘Hidcote’) is hardy to zone 5 only in a protected, very well-drained spot, according to Iowa State.
• Frost heaving. Freeze-thaw cycles push young perennials out of the ground. Leave stems standing over winter and mulch late plantings after the ground freezes.
• Spring frost on blossoms. Plant fruit trees on ground slightly higher than its surroundings so cold air drains away.