Frost dates for Anchorage, Alaska
In Anchorage, half of springs have had their last frost by May 1 (and 1 spring in 10 still has one after May 9), and half of falls have had their first frost by September 29, leaving about 150 frost-free days in a typical year. Here is how sure those dates are, what they mean for planting, and where they come from.
Frost dates for
Anchorage, Alaska
Last spring frost
May 1
Half of springs have their last frost by this date. For a safer bet, wait until May 9: only 1 spring in 10 has a frost after that.
First fall frost
September 29
Half of falls have their first frost by this date. In 1 fall in 10 it comes by September 17.
Growing season
150 days
Frost-free days in a typical year. 9 years in 10 get at least 135.
Hardiness zone
5a
2023 USDA map: the coldest night of winter averages −20°F to −15°F. On the 2012 map it was 4b, half a zone colder. ZIP codes within about 6 miles of the city's center: 7 in 5a and 5 in 5b.
Stations near you disagree. NOAA's Anchorage Merrill Field (less than a mile away, at 140 feet above sea level), the one we used, gives a typical last frost of May 1 and a typical first frost of September 29. NOAA's Campbell Creek Sci Center (5 miles away, at 260 feet above sea level) gives a typical last frost of May 28 and a typical first frost of September 12. So the typical last frost could fall anywhere from May 1 to 28 and the typical first frost from September 12 to 29, depending on whether your garden is more like one or the other. Local terrain matters: hillsides, valley floors, water and city heat can change frost dates a lot over a few miles. Treat the dates here as a starting point, and compare with a nearby gardener or your county extension office.
Print a year planner for Anchorage
Frost risk through the year
How sure are these dates?
A frost date is a probability, not a promise. NOAA worked out, from 30 years of nightly lows, how often the last spring frost and the first fall frost fall on each date. The middle column is the typical year. The outer columns are the early and late years that come about once a decade.
| Early year 1 in 10 | Typical year 1 in 2 | Late year 1 in 10 | |
|---|---|---|---|
| Last frost in spring | April 19 | May 1 | May 9 |
| First frost in fall | September 17 | September 29 | October 12 |
The frost-free season between them runs 150 days in a typical year. In 1 year in 10 it is 167 days or longer, and in 1 year in 10 it is 135 days or shorter.
- Hard freeze (28°F): typically last on April 19 and first on October 8. It is a harder freeze than the 32°F frost line, cold enough to damage many garden plants; how hardy a crop is decides whether it comes through. (The National Weather Service's own hard-freeze threshold varies from office to office.)
- Frost possible (36°F at the station): typically last on May 12 and first on September 20. On clear, still nights the ground can be several degrees colder than the thermometer, so frost can form on plants when the official reading is in the mid-30s.
In 8 springs out of 10, the last frost in Anchorage comes between April 19 and May 9, a window of 20 days. That is narrower than at most NOAA stations (the typical window is 31 days), so the typical date is a steadier guide here than in most places.
Among Alaska's 163 NOAA stations with a frost every year, 81 percent have their typical last frost later than Anchorage does.
Planting calendar for Anchorage
These dates count from the typical last and first frosts, using the planting rules published by Colorado State University Extension (spring), Virginia Cooperative Extension (fall crops) and University of Minnesota Extension (garlic, where winters are hard). Weather in any one year can run early or late, so check the forecast before you plant tender crops.
Your season is too short for a separate fall planting of cabbage: sown late enough to be a fall crop, it wouldn't be ready before the typical first frost. Your spring planting is your harvest.
| When | What to do | Why then |
|---|---|---|
| February | ||
| February 13 to March 13 | Broccoli and cabbage Start seeds indoors | 5 to 7 weeks before planting them out |
| February 27 to March 27 | Cauliflower Start seeds indoors | 5 to 7 weeks before planting out |
| March | ||
| March 13 to April 3 | Eggplant Start seeds indoors | 6 to 9 weeks before planting out |
| March 20 to April 3 | Peppers Start seeds indoors | 6 to 8 weeks before planting out |
| March 27 to April 10 | Tomatoes Start seeds indoors | 5 to 7 weeks before planting out |
| April | ||
| April 3 to 17 | Peas, spinach, lettuce, radishes, onion sets, turnips Sow outdoors, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| April 3 to 17 | Broccoli and cabbage Plant out, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| April 17 to May 1 | Beets, carrots, potatoes, Swiss chard Plant outdoors, as early as | semi-hardy crops: up to 2 weeks before the typical last frost |
| April 17 to May 1 | Cauliflower Plant out, as early as | semi-hardy: up to 2 weeks before the typical last frost |
| May | ||
| May 1 | Snap beans, sweet corn, cucumbers, summer squash Sow outdoors around | tender crops: around the typical last frost date |
| May 15 | Tomatoes, peppers, eggplant Plant out from | very tender: 2 weeks or more after the typical last frost |
| May 15 | Melons, winter squash, pumpkins, lima beans Sow outdoors from | very tender: 2 weeks or more after the typical last frost |
| May 24 to June 7 | Broccoli for fall Start seeds | set the plants out by July 12 |
| July | ||
| July 3 | Snap beans for fall Last date to sow | 60 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| July 7 | Carrots for fall Last date to sow | 70 days to harvest, plus 2 weeks for slower fall growth |
| July 8 | Cucumbers for fall Last date to sow | 55 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| July 12 | Peas for fall Last date to sow | 65 days to harvest, plus 2 weeks for slower fall growth |
| July 13 | Summer squash for fall Last date to sow | 50 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| July 17 | Leaf lettuce and beets for fall Last date to sow | 60 days to harvest, plus 2 weeks for slower fall growth |
| July 27 | Turnips and kohlrabi for fall Last date to sow | 50 days to harvest, plus 2 weeks for slower fall growth |
| August | ||
| August 6 | Spinach for fall Last date to sow | 40 days to harvest, plus 2 weeks for slower fall growth |
| August 16 | Radishes for fall Last date to sow | 30 days to harvest, plus 2 weeks for slower fall growth |
| September | ||
| September 17 | Tomatoes, peppers, squash, melons, cucumbers Watch the forecast from | in 1 fall in 10 the first frost comes by this date; pick tender crops before a frost |
| October | ||
| October 15 to 22 | Garlic Plant cloves | one or two weeks after the typical first hard freeze (28°F), our reading of the first killing frost |
Want more insurance? Shift every spring date 8 days later. That plans around May 9, the date after which only 1 spring in 10 has a frost.
For spring bulbs such as tulips and daffodils, plant once the soil has cooled to about 50 to 55°F and keep going until a couple of weeks before the ground freezes. Our guide to fall planting explains how to tell.
Where these numbers come from
These dates come from NOAA's weather station Anchorage Merrill Field (station USW00026409), less than a mile from the center of Anchorage. It sits at about the same elevation, 140 feet above sea level. NOAA rates this station's record as representative: at least 10 of the 30 years, with the gaps filled from nearby stations.
Our ZIP code lookup matches these 9 ZIP codes to the same station, so they get the same dates: 99501, 99504, 99506, 99507, 99508, 99513, 99516, 99567, 99623. Hardiness zones are worked out separately for each ZIP code.
See frost dates across Alaska, or look up your own ZIP code for the station nearest you. Want the background? Read what a last frost date really means.