USDA zone 5a in Alaska
USDA plant hardiness zone 5a covers 18 locations across Alaska (average annual extreme minimum −20 to −15 °F): Anchorage, AK, Anchorage, AK, Anchorage, AK, Anchorage, AK, Anchorage, AK, Anchorage, AK, and 12 more. Average last spring frost across this group ranges April 21 (Skagway) to June 12 (Cooper Landing), and growing seasons run 75–176 days (Funny River to Skagway) — even within one state, because hardiness sets winter survival, not planting dates. The table below gives every Alaska location's own frost dates; the printable planting calendar uses Anchorage, this group's median-season location.
- USDA zone
- 5a−20 to −15 °F
- Last frost range
- Apr 21–Jun 12avg, 32°F
- First frost range
- Sep 1–Oct 17avg, 32°F
- Growing season range
- 75–176days
Locations in this group
Every location below shares this zone and a nearby weather station, but keeps its own frost dates — find your town for its own numbers, or use the ZIP planner on the home page for an instant personalized answer.
| Location | Also covers | Nearest station | Last frost | First frost | Season (days) |
|---|---|---|---|---|---|
| Anchorage | — | Anchorage Merrill Fld | May 1 | Sep 29 | 150 |
| Anchorage | — | Ft Richardson Wtp | May 9 | Sep 26 | 138 |
| Anchorage * | — | Glen Alps | May 18 | Sep 23 | 125 |
| Anchorage | Beluga | Anchorage Intl Ap | May 5 | Oct 1 | 147 |
| Anchorage | — | Anchorage Lake Hood Ap | May 1 | Oct 3 | 156 |
| Anchorage | — | Eagle Rvr 5 Se | May 21 | Sep 15 | 116 |
| Cooper Landing | — | Cooper Landing 5 W | Jun 12 | Sep 1 | 78 |
| Egegik | — | King Salmon | May 26 | Sep 15 | 111 |
| Funny River | — | Soldotna 5ssw | Jun 11 | Sep 1 | 75 |
| Lazy Mountain | — | Lazy Mtn | May 22 | Sep 16 | 114 |
| Mekoryuk | — | Bethel Ap | May 21 | Sep 22 | 122 |
| Moose Pass | — | Moose Pass 3nw | May 31 | Sep 8 | 99 |
| Point Possession | — | Kenai 29 Ene | Jun 1 | Sep 8 | 94 |
| Skagway | — | Skagway Ap | Apr 21 | Oct 17 | 176 |
| Tatitlek | — | Cannery Creek | May 16 | Oct 3 | 139 |
| Ugashik | — | King Salmon 42 Se | Jun 9 | Sep 11 | 93 |
| Valdez | — | Valdez Wso | Apr 30 | Oct 2 | 157 |
| Wasilla | — | Matanuska Exp Farm | May 14 | Sep 20 | 127 |
* Anchorage is this group's median-season location — the calendar below is computed from its data.
Data: NOAA NCEI U.S. Climate Normals 1991–2020 (public domain) and USDA Plant Hardiness Zone Map 2023. Planting windows synthesized from U.S. Cooperative Extension guides.
Planting calendar (Anchorage, representative)
Computed from Anchorage's average frost dates — the median-season location in this Alaskazone 5a group. hatched = start seeds indoors, solid green = plant out, teal = a fall sowing, and the terracotta dot marks the estimated first harvest. Ranges are extension-guide planning guidance, not guarantees — your own location's dates may run a week or two earlier or later (see the table above).
- Start indoors
- Plant out
- Fall sowing
- First harvest
| Crop | Frost tolerance | Start indoors | Plant out | First harvest | Fall planting | Season fit |
|---|---|---|---|---|---|---|
| Tomato | Tender | Mar 23 – Apr 6 | May 25 – Jun 1 | Jul 24 – Aug 13 | — | matures comfortably |
| Pepper | Very tender | Mar 9 – Mar 23 | Jun 1 – Jun 8 | Jul 31 – Aug 30 | — | matures comfortably |
| Cucumber | Tender | Apr 20 – Apr 27 | May 25 – Jun 1 | Jul 14 – Aug 3 | — | matures comfortably |
| Summer squash / zucchini | Tender | — | May 25 – Jun 1 | Jul 9 – Jul 24 | — | matures comfortably |
| Bush bean | Tender | — | May 25 – Jun 1 | Jul 14 – Jul 24 | Jul 25 – Aug 4 | matures comfortably |
| Sweet corn | Tender | — | May 18 – Jun 1 | Jul 17 – Aug 16 | — | matures comfortably |
| Basil | Very tender | Apr 6 – Apr 20 | May 25 – Jun 1 | Jun 24 – Jul 9 | — | matures comfortably |
| Lettuce | Half-hardy | Apr 6 – Apr 20 | Apr 20 – May 4 | Jun 4 – Jun 19 | Jul 11 – Jul 26 | matures comfortably |
| Pea | Hardy | — | Apr 6 – Apr 20 | May 31 – Jun 15 | Jul 1 – Jul 16 | matures comfortably |
| Spinach | Hardy | — | Apr 6 – Apr 20 | May 16 – May 26 | Jul 21 – Jul 31 | matures comfortably |
| Carrot | Half-hardy | — | Apr 27 – May 4 | Jun 26 – Jul 16 | Jun 21 – Jul 11 | matures comfortably |
| Broccoli | Half-hardy | Mar 23 – Apr 6 | Apr 20 – May 4 | Jun 14 – Jul 4 | Jun 26 – Jul 16 | matures comfortably |
Which crops fit this growing season
Using Anchorage's own 125-day growing season (32°F, NOAA 1991–2020 median) against each crop's real days-to-maturity range: 12 of 12 crops mature here with comfortable margin. A different location in the table above with a longer or shorter season will get a different mix — the ZIP planner on the home page gives your own.
Frost & freeze dates (Anchorage)
From NOAA's 1991–2020 Climate Normals at station USC00503299. The median (p50) is the average date; the 90%-safe column is the date the freeze has passed in about 9 years out of 10 — the conservative date to plant after or harvest before.
| Threshold | Last spring — avg | Last spring — 90%-safe | First fall — avg | First fall — 90%-safe | Season (days) |
|---|---|---|---|---|---|
| 36°F | Jun 5 | Jun 20 | Sep 11 | Sep 24 | 96 |
| 32°F (freeze) | May 18 | May 31 | Sep 23 | Oct 6 | 125 |
| 28°F | May 4 | May 17 | Oct 2 | Oct 17 | 151 |
| 24°F | Apr 21 | May 6 | Oct 12 | Oct 27 | 172 |
Growing degree days
Growing degree days (GDD) accumulate warmth above a base temperature over the year — a better predictor of crop development than the calendar alone. This group's median GDD (base 50°F) across all 18 locations is 551; Anchorage's own reading is shown below.
| Model | °F·days | Used for |
|---|---|---|
| Base 50°F (warm-season) | 281 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 1,353 | cool-season crops (brassicas, greens) |
Hardiness zone 5a in Alaska
Zone 5a means an average annual extreme minimum winter temperature of about −20 to −15 °F on the USDA's 2023 map — the number that tells you which perennials, shrubs, and trees reliably survive an average winter here. It does not set your planting dates, which come from the frost calendar above. Alaska spans 16 hardiness zones in this dataset — see all Alaska locations for the full range, including zones1a, 1b, 2a, 2b, 3a, 3b, 4a, 4b, 5b, 6a, 6b, 7a, 7b, 8a, 8b.
Explore zone 5a in other states at zone 5a, or see all USDA hardiness zones.
Frequently asked questions
- What does USDA hardiness zone 5a mean in Alaska?
- Zone 5a means an average annual extreme minimum winter temperature of −20 to −15 °F — the standard USDA measure of which perennials survive winter. 18 locations in Alaska fall in this zone. It does not set planting dates; see the frost calendar below for that.
- Where in Alaska's zone 5a is the growing season longest?
- Skagway runs the longest season on this page at about 176 days; Funny River is shortest at about 75 days — they share the same hardiness zone, but they sit at different weather stations, so their frost calendars differ.
- When should I plant tomatoes in Alaska's zone 5a?
- Using Anchorage's frost dates (this page's median-season location): start seeds indoors about Mar 23 – Apr 6, then transplant outside about May 25 – Jun 1. Your own location in the table above may differ by a week or two — use the ZIP planner on the home page for your exact station's dates.
- Does every location in Alaska's zone 5a have the same frost dates?
- No — they do not all share a weather station, so frost dates vary by a week or more across the 18 locations listed (see the table above for each location's own dates).
Sources & method
Frost, freeze, growing-season, and growing-degree-day figures are NOAA NCEI U.S. Climate Normals 1991–2020, one reading per location's own nearest station (see the table above). The hardiness zone is the USDA Plant Hardiness Zone Map 2023, matched to each location's ZIP. Planting windows are computed by counting from the average last and first frost using per-crop offsets synthesized from U.S. Cooperative Extension guides — the full method and citations are on the methodology page.