Union, OR planting calendar
- USDA zone
- 6b−5 to 0 °F
- Last frost
- May 11avg, 32°F
- First frost
- Sep 26avg, 32°F
- Growing season
- 136days
Union, Oregon is in USDA plant hardiness zone 6b. Its average last spring frost is around May 11 and the first fall frost around September 26, giving a growing season of about 136 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.
Union planting calendar
Each crop's windows are counted from Union'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 16 – Mar 30 | May 18 – May 25 | Jul 17 – Aug 6 | — |
| Pepper | Very tender | Mar 2 – Mar 16 | May 25 – Jun 1 | Jul 24 – Aug 23 | — |
| Cucumber | Tender | Apr 13 – Apr 20 | May 18 – May 25 | Jul 7 – Jul 27 | — |
| Summer squash / zucchini | Tender | — | May 18 – May 25 | Jul 2 – Jul 17 | — |
| Bush bean | Tender | — | May 18 – May 25 | Jul 7 – Jul 17 | Jul 28 – Aug 7 |
| Sweet corn | Tender | — | May 11 – May 25 | Jul 10 – Aug 9 | — |
| Basil | Very tender | Mar 30 – Apr 13 | May 18 – May 25 | Jun 17 – Jul 2 | — |
| Lettuce | Half-hardy | Mar 30 – Apr 13 | Apr 13 – Apr 27 | May 28 – Jun 12 | Jul 14 – Jul 29 |
| Pea | Hardy | — | Mar 30 – Apr 13 | May 24 – Jun 8 | Jul 4 – Jul 19 |
| Spinach | Hardy | — | Mar 30 – Apr 13 | May 9 – May 19 | Jul 24 – Aug 3 |
| Carrot | Half-hardy | — | Apr 20 – Apr 27 | Jun 19 – Jul 9 | Jun 24 – Jul 14 |
| Broccoli | Half-hardy | Mar 16 – Mar 30 | Apr 13 – Apr 27 | Jun 7 – Jun 27 | Jun 29 – Jul 19 |
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 USC00358746. 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 | Jun 2 | Jun 23 | Sep 10 | Sep 26 | 101 |
| 32°F (freeze) | May 11 | May 31 | Sep 26 | Oct 10 | 136 |
| 28°F | Apr 24 | May 10 | Oct 7 | Oct 23 | 166 |
| 24°F | Apr 3 | Apr 22 | Oct 21 | Nov 11 | 202 |
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) | 2,086 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 4,160 | cool-season crops (brassicas, greens) |
Hardiness zone 6b
Union sits in USDA plant hardiness zone 6b on the 2023 map — meaning its average annual extreme minimum winter temperature is about −5 to 0 °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 6b, or see all USDA hardiness zones.
Frequently asked questions
- What USDA hardiness zone is Union?
- Union, Oregon is in USDA plant hardiness zone 6b on the 2023 map (average annual extreme minimum temperature −5 to 0 °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 Union?
- The average (median) last spring frost at 32°F is around May 11, 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 31, so wait until then before setting out frost-tender plants if you want to be safe.
- When is the first fall frost in Union?
- The average first fall frost at 32°F is around September 26. That leaves a growing season of about 136 days between the average last spring and first fall frosts.
- When should I start tomatoes in Union?
- Start tomato seeds indoors about Mar 16 – Mar 30 and transplant them outside about May 18 – May 25, once the danger of frost has passed. Estimated first harvest is around Jul 17 – Aug 6.
- How long is the growing season in Union?
- About 136 days at the 32°F threshold (NOAA 1991–2020, median) — the span between the average last spring frost (~May 11) and the average first fall frost (~September 26). 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 USC00358746 (Union, 16.8 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.