How Long Does Frost Risk Last in Your Area?
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GardenSays
In Minneapolis, MN, frost stays a real risk until about May 19, and returns to watch-the-forecast territory around Sep 21.
- Spring risk until
- ~May 19
- Low-risk window
- May 19 – Sep 21
- Fall watch from
- ~Sep 21
Frost risk isn't a single date — it tapers. In Minneapolis, MN the average last frost is May 5, but because averages are ~50/50, the practical rule is: until about May 19, check the overnight forecast before leaving tender plants unprotected. Between May 19 and Sep 21, frost is unlikely in a typical year.
- These dates are NOAA climate normals (long-term averages), not a forecast. For frost risk tonight, check your local forecast — the NWS issues frost advisories when surface temperatures are expected in the mid-30s °F, because frost can form on plants before the air officially hits 32°F.
Typical estimate · 4 verified sources · No live weather · Checked 2026-07-17 · How we decide
Why
From Sep 21 onward, the fall watch begins: the average first frost is Oct 5, and covering plants on the first cold night often buys weeks of extra harvest.
- An "average" frost date is roughly a coin flip: in about half of years, frost still comes after the average last-frost date. Buffers turn that coin flip into good odds.
- Three different events: frost (ice on leaves, possible with air temps in the mid-30s °F) burns tender crops; a freeze at 32°F kills tender and very-tender crops; a hard freeze at 28°F or below kills most unprotected vegetation (NWS). Hardy crops like peas and spinach shrug off frost but not a prolonged hard freeze.
- The NWS issues frost advisories when surface temperatures are expected in the mid-30s °F — frost can form on leaves before the thermometer reads 32°F.
When this doesn't apply
- Microclimates shift these dates: low spots and frost pockets run 1-2 weeks riskier, urban cores and near-water gardens 1-2 weeks safer.
How this was calculated
- 1. Average last spring frostMay 5Source guidance
Minneapolis, MN: typical last 32°F morning, NOAA 1991-2020 normals
- 2. Average first fall frostOct 5Source guidance
Minneapolis, MN: typical first 32°F morning of fall
- 3. Growing season153 daysCalculated result
Days between the average last and first frost
- 4. Risk buffer±14 daysGardenSays estimate
±14 days around the average dates — our estimate for the watch-the-forecast window
Data sources
- NOAA NCEI — 1991-2020 U.S. Climate Normals (freeze date probabilities) (checked 2026-07-15)
- National Gardening Association — frost date lookup (checked 2026-07-15)
- NOAA National Weather Service — Frost Advisory (glossary) — Frost advisories are issued when widespread frost is expected; surface temperatures are usually in the mid 30s Fahrenheit. (checked 2026-07-16)
- NOAA National Weather Service — Hard Freeze (glossary) — A hard freeze occurs when the surface air temperature reaches 28°F or lower for an extended period, killing most types of vegetation. (checked 2026-07-17)
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People also ask
When is my average last frost date?
Your average last frost in Minneapolis, MN is around May 5 — tender plants are safest outside from about May 12. Calculate yours →
When is my average first fall frost?
Your average first fall frost in Minneapolis, MN is around Oct 5 — plan fall crops and frost protection back from that date. Calculate yours →
At what temperature should I cover my plants?
When is it safe to plant tomatoes outside?
Start tomato seeds indoors Mar 17 – Mar 31; transplant once frost danger is past and soil has warmed to ~60°F — typically May 12 – May 19 here. Calculate yours →
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