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

Planting zone for 99833 — Petersburg, AK

ZIP code 99833 (Petersburg, Petersburg County) is in USDA zone 7b: the coldest winter night averages 5 to 10 °F. The median last spring frost is April 29 and the first fall frost October 17.

Where ZIP 99833 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.

Zone7b5 to 10 °F
Coldest night−15 to −12.2 °C
Last frostApr 29
First frostOct 17
2012 zone7a

Was 7a 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 7b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Petersburg, AK…

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 Petersburg, AK

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 29median — 50% chance of a later frost
Safe for tender plantsMay 14only 10% chance of frost after
First fall frostOctober 17median — 10% chance by Sep 30
Growing season169 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 11 and returns around November 1.

From the NOAA station Petersburg 1, AK — 10 miles away, elevation 108 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 99833

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 18 – Apr 1
SpinachSow outdoors · Mar 18 – Apr 8
Broccoli, cabbageStart indoors · Feb 18 – Mar 4
Broccoli, cabbageTransplant · Apr 8 – Apr 22
Onion setsPlant outdoors · Apr 1 – Apr 15
PotatoesPlant outdoors · Apr 8 – Apr 22
LettuceSow outdoors · Apr 1 – Apr 15
Carrots, beetsSow outdoors · Apr 8 – Apr 22
TomatoesStart indoors · Mar 4 – Mar 18
TomatoesTransplant · May 6 – May 20
Peppers, eggplantStart indoors · Feb 18 – Mar 4
Peppers, eggplantTransplant · May 13 – May 27
BeansSow outdoors · May 6 – May 20
Sweet cornSow outdoors · May 6 – May 20
Cucumbers, squashSow outdoors · May 6 – May 20
Fall lettuce, spinachSow outdoors · Aug 22 – Sep 5
GarlicPlant cloves · Oct 3 – Nov 7
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 29) and first fall frost (Oct 17) 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.

Native plants for zone 7b in Alaska

289 plants native to Alaska, recorded in Alaska, and rated by the USDA to survive 5 °F or colder — the bottom of zone 7b. Each links to its USDA PLANTS profile.

Trees 16

Alaska cedar75 ft · blooms mid spring · low shade tolerance · to −22 °Fbalsam poplar80 ft · blooms late spring · high shade tolerance · to −79 °Fblack spruce65 ft · blooms late spring · low shade tolerance · to −79 °Flodgepole pine99 ft · blooms mid summer · high shade tolerance · to −70 °Fmountain hemlock125 ft · blooms early summer · low shade tolerance · to −18 °FPacific silver fir165 ft · blooms late spring · low shade tolerance · to −28 °F

Shrubs 50

alpine bearberry0.5 ft · blooms early spring · medium shade tolerance · to −62 °Falpine laurel1 ft · blooms late spring · low shade tolerance · to −28 °FBarclay's willow15 ft · high shade tolerance · to −43 °Fblack crowberry1 ft · blooms mid summer · high shade tolerance · to −43 °Fblack hawthorn15 ft · blooms mid spring · medium shade tolerance · to −47 °Fbog blueberry2 ft · blooms early summer · medium shade tolerance · to −38 °F

Wildflowers & perennials 125

alkali buttercup1 ft · blooms late spring · low shade tolerance · to −38 °Falpine aster0.3 ft · blooms early summer · medium shade tolerance · to −28 °Falpine bistort1 ft · blooms mid spring · high shade tolerance · to −38 °Falpine mountainsorrel1 ft · blooms mid summer · medium shade tolerance · to −43 °Falpine sweetvetch2 ft · blooms early summer · high shade tolerance · to −62 °FAmerican alpine speedwell1 ft · blooms summer · medium shade tolerance · to −28 °F

Grasses 89

Alaska brome5 ft · blooms late spring · low shade tolerance · to −18 °FAlaska oniongrass3 ft · blooms mid spring · low shade tolerance · to −33 °FAlpine Meadow-Foxtail0.5 ft · blooms mid spring · medium shade tolerance · to −33 °Falpine timothy1.4 ft · blooms late spring · medium shade tolerance · to −43 °Farctic bluegrass2 ft · high shade tolerance · to −62 °Fawlfruit sedge4 ft · blooms mid spring · low shade tolerance · to −38 °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 Petersburg, AK.

Soil in Petersburg, AK

The soil mapped at the center of ZIP 99833 is Mosman — very gravelly loam, well drained.

TextureVery gravelly loama good balance for most vegetables
pH4.8strongly acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter10%high
Hydrologic groupDwater soaks in very slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Mosman-Kupreanof complex, 75 to 110 percent slopes.

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 99833; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Petersburg, AK

Summer high62 °Faverage high, July
Winter low27 °Faverage low, January
Hot days0days a year at 90 °F or more
Freezing nights115nights a year at 32 °F or less
Growing degree days610base 50 °F — the season’s usable heat
Longest day17 h 51 mindaylight on June 21
Shortest day6 h 45 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation110.2 inper year, rain and melted snow
Snowfall86 inper year; 66 days with snow on the ground

Average high and low, by month

20°30°40°50°60°70°32 °FJanuary: average high 35 °F, low 27 °F 35°27° JanFebruary: average high 37 °F, low 28 °F 37°28° FebMarch: average high 40 °F, low 30 °F 40°30° MarApril: average high 48 °F, low 35 °F 48°35° AprMay: average high 55 °F, low 42 °F 55°42° MayJune: average high 60 °F, low 48 °F 60°48° JunJuly: average high 62 °F, low 51 °F 62°51° JulAugust: average high 61 °F, low 50 °F 61°50° AugSeptember: average high 56 °F, low 46 °F 56°46° SepOctober: average high 47 °F, low 39 °F 47°39° OctNovember: average high 39 °F, low 32 °F 39°32° NovDecember: average high 35 °F, low 28 °F 35°28° Dec

Precipitation by month inches · ❄ = snowfall

0″2″4″6″8″10″12″14″January: 11.39 in precipitation, 20.7 in snowfall 11.4❄21 JanFebruary: 7.60 in precipitation, 16.9 in snowfall 7.6❄17 FebMarch: 7.60 in precipitation, 20 in snowfall 7.6❄20 MarApril: 6.66 in precipitation, 1.1 in snowfall 6.7❄1 AprMay: 5.86 in precipitation, 0.2 in snowfall 5.9 MayJune: 4.98 in precipitation 5.0 JunJuly: 5.63 in precipitation 5.6 JulAugust: 8.21 in precipitation 8.2 AugSeptember: 14.35 in precipitation 14.3 SepOctober: 13.84 in precipitation, 0.4 in snowfall 13.8 OctNovember: 12.28 in precipitation, 10.8 in snowfall 12.3❄11 NovDecember: 11.79 in precipitation, 15.5 in snowfall 11.8❄16 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Petersburg 1, AK (10 mi away); precipitation: Petersburg 1, AK (10 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

998307b
Kake, AK · 34 mi
999278a
Point Baker, AK · 39 mi
998207a
Angoon, AK · 55 mi
999297b
Wrangell, AK · 64 mi
999188a
Coffman Cove, AK · 67 mi
999197b
Thorne Bay, AK · 87 mi
999037b
Meyers Chuck, AK · 87 mi
999257b
Klawock, AK · 90 mi

Alaska planting zones →

Questions about 99833

What planting zone is ZIP code 99833?

ZIP code 99833 (Petersburg, AK) is in USDA hardiness zone 7b on the 2023 map: the coldest night of an average winter reaches 5 to 10 °F (−15 to −12.2 °C).

When is the last frost in Petersburg, AK?

The median last spring frost (32 °F) near 99833 is April 29; after May 14 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Petersburg 1 station.

When is the first frost in Petersburg, AK?

The median first fall frost near 99833 is October 17, giving a median frost-free growing season of 169 days.

When should I plant tomatoes in 99833?

Start tomato seeds indoors around Mar 4 – Mar 18 and set transplants outside around May 6 – May 20, one to three weeks after the median last frost.

How much rain and snow does 99833 get?

About 110.2 inches of precipitation a year and 86 inches of snowfall (NOAA 1991–2020 normals, Petersburg 1 station).

How hot do summers get in Petersburg, AK?

The average high peaks at 62 °F in July, with about 0 days a year at 90 °F or more.

What kind of soil does 99833 have?

The USDA soil survey maps Mosman at the center of ZIP 99833: very gravelly loam, well drained, pH about 4.8 (strongly acidic).

What kind of onions grow in Petersburg, AK?

Long-day onions: the longest day near 99833 is 17 h 51 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 99833 change?

Yes. The 2012 USDA map put 99833 in zone 7a; the 2023 map puts it in zone 7b. The newer map uses 1991–2020 data and more weather stations.