Ann Arbor, MI 48109 planting calendar
- USDA zone
- 6a−10 to −5 °F
- Last frost
- May 3avg, 32°F
- First frost
- Oct 13avg, 32°F
- Growing season
- 160days
Ann Arbor, Michigan is in USDA plant hardiness zone 6a. Its average last spring frost is around May 3 and the first fall frost around October 13, giving a growing season of about 160 days (NOAA 1991–2020 normals, 32°F, median). Start tender crops like tomatoes and peppers indoors weeks before the last frost and set them out afterward; sow hardy crops such as peas, spinach, and lettuce before it. The planner below turns those frost dates into a printable per-crop planting calendar.
Ann Arbor planting calendar
Each crop's windows are counted from Ann Arbor's average frost dates. 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.
- Start indoors
- Plant out
- Fall sowing
- First harvest
| Crop | Frost tolerance | Start indoors | Plant out | First harvest | Fall planting |
|---|---|---|---|---|---|
| Tomato | Tender | Mar 8 – Mar 22 | May 10 – May 17 | Jul 9 – Jul 29 | — |
| Pepper | Very tender | Feb 22 – Mar 8 | May 17 – May 24 | Jul 16 – Aug 15 | — |
| Cucumber | Tender | Apr 5 – Apr 12 | May 10 – May 17 | Jun 29 – Jul 19 | — |
| Summer squash / zucchini | Tender | — | May 10 – May 17 | Jun 24 – Jul 9 | — |
| Bush bean | Tender | — | May 10 – May 17 | Jun 29 – Jul 9 | Aug 14 – Aug 24 |
| Sweet corn | Tender | — | May 3 – May 17 | Jul 2 – Aug 1 | — |
| Basil | Very tender | Mar 22 – Apr 5 | May 10 – May 17 | Jun 9 – Jun 24 | — |
| Lettuce | Half-hardy | Mar 22 – Apr 5 | Apr 5 – Apr 19 | May 20 – Jun 4 | Jul 31 – Aug 15 |
| Pea | Hardy | — | Mar 22 – Apr 5 | May 16 – May 31 | Jul 21 – Aug 5 |
| Spinach | Hardy | — | Mar 22 – Apr 5 | May 1 – May 11 | Aug 10 – Aug 20 |
| Carrot | Half-hardy | — | Apr 12 – Apr 19 | Jun 11 – Jul 1 | Jul 11 – Jul 31 |
| Broccoli | Half-hardy | Mar 8 – Mar 22 | Apr 5 – Apr 19 | May 30 – Jun 19 | Jul 16 – Aug 5 |
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.
Frost & freeze dates
From NOAA's 1991–2020 Climate Normals at station USC00200230. 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 (p10 for spring, p90 for fall) — 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 | May 16 | May 31 | Oct 2 | Oct 14 | 138 |
| 32°F (freeze) | May 3 | May 20 | Oct 13 | Oct 27 | 160 |
| 28°F | Apr 23 | May 9 | Oct 26 | Nov 8 | 183 |
| 24°F | Apr 11 | Apr 26 | Nov 6 | Nov 20 | 209 |
32°F is the standard "freeze" line that damages tender crops; lighter 36°F frost can nip the most cold-sensitive plants, while hardy crops shrug off light frost down toward 28°F. Use the threshold that matches what you are protecting.
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. Warm-season crops need a long, warm GDD total; a short, cool GDD total favors greens and brassicas.
| Model | °F·days | Used for |
|---|---|---|
| Base 50°F (warm-season) | 2,801 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 4,894 | cool-season crops (brassicas, greens) |
Hardiness zone 6a
Ann Arbor sits in USDA plant hardiness zone 6a on the 2023 map — meaning its average annual extreme minimum winter temperature is about −10 to −5 °F. That number 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.
Explore more places in zone 6a, or see all USDA hardiness zones.
Frequently asked questions
- What USDA hardiness zone is Ann Arbor?
- Ann Arbor, Michigan is in USDA plant hardiness zone 6a on the 2023 map (average annual extreme minimum temperature −10 to −5 °F) — from the USDA Plant Hardiness Zone Map 2023, matched to this location's ZIP. See the methodology page for sources.
- When is the last frost in Ann Arbor?
- The average (median) last spring frost at 32°F is around May 3, from NOAA's 1991–2020 climate normals at the nearest reporting station. Roughly one year in ten the last frost is as late as May 20, so wait until then before setting out frost-tender plants if you want to be safe.
- When is the first fall frost in Ann Arbor?
- The average first fall frost at 32°F is around October 13. That leaves a growing season of about 160 days between the average last spring and first fall frosts.
- When should I start tomatoes in Ann Arbor?
- Start tomato seeds indoors about Mar 8 – Mar 22 and transplant them outside about May 10 – May 17, once the danger of frost has passed. Estimated first harvest is around Jul 9 – Jul 29.
- How long is the growing season in Ann Arbor?
- About 160 days at the 32°F threshold (NOAA 1991–2020, median) — the span between the average last spring frost (~May 3) and the average first fall frost (~October 13). Cold-hardy crops extend usable time at both ends; frost-tender crops fit inside it.
Sources & method
Frost, freeze, growing-season, and growing-degree-day figures are NOAA NCEI U.S. Climate Normals 1991–2020 for station USC00200230 (Ann Arbor U Of Mich, 3.7 km away). The hardiness zone is the USDA Plant Hardiness Zone Map 2023, matched to this 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.