Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated

Planting zone for 49918 — Copper Harbor, MI

ZIP code 49918 (Copper Harbor, Keweenaw County) is in USDA zone 6a: the coldest winter night averages −10 to −5 °F. The median last spring frost is May 20 and the first fall frost October 15.

Where ZIP 49918 is

Outlined: the ZIP code area · tap the map for the zone at any spot · scroll or pinch to zoom

Not the official USDA Plant Hardiness Zone Map. Zones come from the 2023 USDA hardiness-zone data by the PRISM Group, Oregon State University; we re-mapped and recolored them. The official map is at planthardiness.ars.usda.gov.

Zone6a−10 to −5 °F
Coldest night−23.3 to −20.6 °C
Last frostMay 20
First frostOct 15
2012 zone5b

Was 5b on the 2012 map — half a zone warmer now. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 6a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Copper Harbor, MI…

Forecast data: National Weather Service (api.weather.gov), public domain. This is not a warning service — for official frost and freeze warnings see weather.gov.

Frost dates in Copper Harbor, MI

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 20median — 50% chance of a later frost
Safe for tender plantsJune 3only 10% chance of frost after
First fall frostOctober 15median — 10% chance by Sep 30
Growing season148 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 4 and returns around October 29.

From the NOAA station Copper Harbor Ft Wilkins, MI — 2 miles away, elevation 627 ft. NOAA NCEI U.S. Climate Normals 1991–2020, 32 °F threshold. Low spots and valleys can freeze later in spring than the station.

When to plant vegetables in 49918

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Apr 8 – Apr 22
SpinachSow outdoors · Apr 8 – Apr 29
Broccoli, cabbageStart indoors · Mar 11 – Mar 25
Broccoli, cabbageTransplant · Apr 29 – May 13
Onion setsPlant outdoors · Apr 22 – May 6
PotatoesPlant outdoors · Apr 29 – May 13
LettuceSow outdoors · Apr 22 – May 6
Carrots, beetsSow outdoors · Apr 29 – May 13
TomatoesStart indoors · Mar 25 – Apr 8
TomatoesTransplant · May 27 – Jun 10
Peppers, eggplantStart indoors · Mar 11 – Mar 25
Peppers, eggplantTransplant · Jun 3 – Jun 17
BeansSow outdoors · May 27 – Jun 10
Sweet cornSow outdoors · May 27 – Jun 10
Cucumbers, squashSow outdoors · May 27 – Jun 10
Fall lettuce, spinachSow outdoors · Aug 20 – Sep 3
GarlicPlant cloves · Oct 1 – Nov 5
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 20) and first fall frost (Oct 15) with the rules of thumb U.S. extension services publish. Cool-season crops take a light frost; warm-season crops do best once the soil is above about 60 °F.

When spring arrived in 2026

In 2026, spring leaf-out near 49918 came on May 8 — 5 days later than the 1991–2020 average (May 3).

JanFebMarAprMayJun

The Spring Index marks the day when accumulated warmth is enough for lilac and honeysuckle to leaf out — a widely used signal that the growing season has started. Source: USA National Phenology Network, www.usanpn.org — Spring Indices, first leaf, 2026 (data as of 2026-09-08) and 30-year average 1991–2020 (CC BY 4.0).

Native plants for zone 6a in Michigan

580 plants native to the lower 48 states, recorded in Michigan, and rated by the USDA to survive −10 °F or colder — the bottom of zone 6a. Each links to its USDA PLANTS profile.

Trees 58

American basswood100 ft · blooms late spring · low shade tolerance · to −46 °FAmerican beech80 ft · blooms mid spring · low shade tolerance · to −44 °FAmerican chestnut115 ft · blooms early summer · high shade tolerance · to −33 °FAmerican elm120 ft · blooms early spring · medium shade tolerance · to −46 °FAmerican sycamore100 ft · blooms spring · medium shade tolerance · to −34 °Farborvitae50 ft · blooms mid spring · medium shade tolerance · to −33 °F

Shrubs 105

alderleaf buckthorn3 ft · blooms late spring · low shade tolerance · to −33 °FAllegheny serviceberry35 ft · blooms early spring · low shade tolerance · to −38 °Falternateleaf dogwood25 ft · blooms mid spring · low shade tolerance · to −47 °FAmerican black currant3 ft · blooms early spring · to −46 °FAmerican hazelnut10 ft · blooms spring · medium shade tolerance · to −33 °FAmerican hornbeam30 ft · blooms mid spring · low shade tolerance · to −34 °F

Wildflowers & perennials 220

alkali buttercup1 ft · blooms late spring · low shade tolerance · to −38 °Falpine bistort1 ft · blooms mid spring · high shade tolerance · to −38 °Falpine sweetvetch2 ft · blooms early summer · high shade tolerance · to −62 °FAmerican bur-reed3 ft · blooms indeterminate · medium shade tolerance · to −33 °FAmerican eelgrass1 ft · blooms mid summer · high shade tolerance · to −33 °FAmerican lotus3 ft · blooms mid summer · high shade tolerance · to −36 °F

Grasses 174

alpine timothy1.4 ft · blooms late spring · medium shade tolerance · to −43 °FAmerican beachgrass2.5 ft · blooms spring · high shade tolerance · to −28 °Farctic brome3 ft · blooms early summer · low shade tolerance · to −33 °Fawlfruit sedge4 ft · blooms mid spring · low shade tolerance · to −38 °Fbeaked sedge4 ft · blooms late spring · low shade tolerance · to −38 °Fbeaked spikerush3 ft · blooms late spring · high shade tolerance · to −28 °F

Vines 8

American bittersweet15 ft · blooms spring · low shade tolerance · to −38 °Fdevil's darning needles15 ft · blooms mid summer · medium shade tolerance · to −38 °Ffrost grape83 ft · blooms late spring · medium shade tolerance · to −23 °Friverbank grape45 ft · blooms late spring · medium shade tolerance · to −33 °Fsummer grape30 ft · blooms late spring · low shade tolerance · to −23 °Ftrumpet creeper2 ft · blooms summer · high shade tolerance · to −13 °F

Source: USDA, NRCS. 2026. The PLANTS Database (plants.usda.gov), National Plant Data Team — state distribution, native status and the “Temperature, Minimum” characteristic. Check light, moisture and soil needs before buying; local nurseries and your state native plant society can confirm what thrives in Copper Harbor, MI.

Soil in Copper Harbor, MI

The soil mapped at the center of ZIP 49918 is Arcadian — highly decomposed plant material, well drained.

TextureHighly decomposed plant materialtop layer
pH4.8strongly acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter75%high
Hydrologic groupDwater soaks in very slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Arcadian-Dishno-Rock outcrop complex, dissected, 8 to 35 percent slopes, very bouldery.

Soil Survey Staff, Natural Resources Conservation Service, USDA. Soil Survey Geographic (SSURGO) Database, via Soil Data Access, accessed 2026-10-29. The soil at the center point of ZIP 49918; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Copper Harbor, MI

Summer high73 °Faverage high, July
Winter low10 °Faverage low, February
Hot days1days a year at 90 °F or more
Freezing nights167nights a year at 32 °F or less
Growing degree days1,504base 50 °F — the season’s usable heat
Longest day15 h 58 mindaylight on June 21
Shortest day8 h 27 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation33.1 inper year, rain and melted snow

Average high and low, by month

0°10°20°30°40°50°60°70°80°32 °FJanuary: average high 23 °F, low 11 °F 23°11° JanFebruary: average high 25 °F, low 10 °F 25°10° FebMarch: average high 34 °F, low 17 °F 34°17° MarApril: average high 44 °F, low 28 °F 44°28° AprMay: average high 57 °F, low 39 °F 57°39° MayJune: average high 67 °F, low 46 °F 67°46° JunJuly: average high 73 °F, low 54 °F 73°54° JulAugust: average high 73 °F, low 56 °F 73°56° AugSeptember: average high 66 °F, low 50 °F 66°50° SepOctober: average high 52 °F, low 39 °F 52°39° OctNovember: average high 39 °F, low 28 °F 39°28° NovDecember: average high 29 °F, low 18 °F 29°18° Dec

Precipitation by month inches

0″1″2″3″4″January: 2.24 in precipitation 2.2 JanFebruary: 1.89 in precipitation 1.9 FebMarch: 1.70 in precipitation 1.7 MarApril: 2.68 in precipitation 2.7 AprMay: 3.55 in precipitation 3.5 MayJune: 3.07 in precipitation 3.1 JunJuly: 3.02 in precipitation 3.0 JulAugust: 2.63 in precipitation 2.6 AugSeptember: 3.71 in precipitation 3.7 SepOctober: 3.72 in precipitation 3.7 OctNovember: 2.60 in precipitation 2.6 NovDecember: 2.33 in precipitation 2.3 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Copper Harbor Ft Wilkins, MI (2 mi away); precipitation: Copper Harbor Ft Wilkins, MI (2 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

8 of the 8 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

499505b
Mohawk, MI · 15 mi
499175b
Copper City, MI · 27 mi
498055b
Allouez, MI · 27 mi
499015b
Ahmeek, MI · 28 mi
499425b
Kearsarge, MI · 30 mi
499455b
Lake Linden, MI · 31 mi
499135b
Calumet, MI · 32 mi
499345b
Hubbell, MI · 34 mi

Michigan planting zones →

Questions about 49918

What planting zone is ZIP code 49918?

ZIP code 49918 (Copper Harbor, MI) is in USDA hardiness zone 6a on the 2023 map: the coldest night of an average winter reaches −10 to −5 °F (−23.3 to −20.6 °C).

When is the last frost in Copper Harbor, MI?

The median last spring frost (32 °F) near 49918 is May 20; after June 3 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Copper Harbor Ft Wilkins station.

When is the first frost in Copper Harbor, MI?

The median first fall frost near 49918 is October 15, giving a median frost-free growing season of 148 days.

When should I plant tomatoes in 49918?

Start tomato seeds indoors around Mar 25 – Apr 8 and set transplants outside around May 27 – Jun 10, one to three weeks after the median last frost.

How much rain and snow does 49918 get?

About 33.1 inches of precipitation a year (NOAA 1991–2020 normals, Copper Harbor Ft Wilkins station).

How hot do summers get in Copper Harbor, MI?

The average high peaks at 73 °F in July, with about 1 days a year at 90 °F or more.

What kind of soil does 49918 have?

The USDA soil survey maps Arcadian at the center of ZIP 49918: highly decomposed plant material, well drained, pH about 4.8 (strongly acidic).

Did spring come early in Copper Harbor, MI in 2026?

Spring leaf-out near 49918 came on May 8 in 2026, 5 days later than the 1991–2020 average (May 3), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Copper Harbor, MI?

Long-day onions: the longest day near 49918 is 15 h 58 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 49918 change?

Yes. The 2012 USDA map put 49918 in zone 5b; the 2023 map puts it in zone 6a. The newer map uses 1991–2020 data and more weather stations.