Zone 6a: What Grows and How to Garden There

What a zone 6a winter means

Zone 6a winters are mild enough for almost every perennial, shrub and fruit grown in the northern states, and cold enough to hold back many plants from the South. The coldest night of a typical 6a winter lands close to the temperature at which peach and sweet cherry flower buds start dying, which Virginia Tech puts at about -10°F. Illinois Extension adds that each degree below that kills roughly another 10% of the buds. In most winters you get peaches; after a hard one you may not.

Where zone 6a is

Zone 6a runs across the Midwest from Chicago and the Illinois prairie through Indianapolis and northern Indiana, northern Ohio and the lower Michigan cities of Grand Rapids and Ann Arbor, then east through central New York around Syracuse, central Pennsylvania and the interior of Massachusetts, Connecticut and southern New Hampshire. On the Plains it includes Omaha, Lincoln and parts of Kansas and Missouri, and in the West the Denver area, Colorado Springs, northern Utah valleys and parts of Idaho, Washington and Oregon east of the Cascades.

Fruit trees and small fruit

Apples and pears are hardy to about -25°F (Virginia Tech) and are the safest tree fruit. Tart and sweet cherries, plums and peaches all grow here, but they bloom early, and Penn State’s frost table shows the risk: at full bloom, peach flowers suffer about 10% kill at 27°F and 90% at 24°F, and apples about 10% at 28°F. A site slightly above its surroundings lets cold air drain away on frosty nights.

For blueberries, Ohio State recommends northern highbush types; rabbiteye and southern highbush are bred for the South.

Figs are borderline. ‘Hardy Chicago’, ‘Brown Turkey’ and ‘Celeste’ are the cultivars Extension services name for cold areas. Rutgers protects figs once leaves drop, around Thanksgiving, by wrapping in burlap and paper (no plastic) or by caging and filling with leaves.

Perennials, bulbs and shrubs

Peonies, hostas, daylilies, purple coneflower, lilies, tulips and daffodils are all comfortably hardy. Common boxwood is rated to zone 5a by NC State.

Plants at their limit here include:

• Bigleaf hydrangea: NC State rates it to 6a, but stems often die back and flower buds are lost in cold winters. Reblooming types that flower on new wood, or smooth and panicle hydrangeas, are more dependable (Cornell).
• Crape myrtle: survives but often dies back (Virginia Tech, NC State).
• Camellias: most are hardy only to zone 7. Virginia Tech specialists say the Ackerman hybrids, bred from tea-oil camellia, are hardy to zones 6a-6b.
• Azaleas and rhododendrons: grow well with morning sun and afternoon shade out of the wind; Nebraska Extension advises no fertilizer after July 1.

Special concerns

Mulch late-planted perennials after the ground freezes to prevent heaving, and leave stems of marginal perennials such as mums standing over winter. In the Denver area, dry winter wind is as damaging as cold: water evergreens during long dry spells.