Sullivan, TX planting calendar
- USDA zone
- 10a30 to 35 °F
- Last frost
- Jan 31avg, 32°F
- First frost
- Dec 17avg, 32°F
- Growing season
- 321days
Sullivan, Texas is in USDA plant hardiness zone 10a. Its average last spring frost is around January 31 and the first fall frost around December 17, giving a growing season of about 321 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.
Sullivan planting calendar
Each crop's windows are counted from Sullivan'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 | Jan 1 | Feb 7 – Feb 14 | Apr 8 – Apr 28 | — |
| Pepper | Very tender | Jan 1 | Feb 14 – Feb 21 | Apr 15 – May 15 | — |
| Cucumber | Tender | Jan 3 – Jan 10 | Feb 7 – Feb 14 | Mar 29 – Apr 18 | — |
| Summer squash / zucchini | Tender | — | Feb 7 – Feb 14 | Mar 24 – Apr 8 | — |
| Bush bean | Tender | — | Feb 7 – Feb 14 | Mar 29 – Apr 8 | Oct 18 – Oct 28 |
| Sweet corn | Tender | — | Jan 31 – Feb 14 | Apr 1 – May 1 | — |
| Basil | Very tender | Jan 1 – Jan 3 | Feb 7 – Feb 14 | Mar 9 – Mar 24 | — |
| Lettuce | Half-hardy | Jan 1 – Jan 3 | Jan 3 – Jan 17 | Feb 17 – Mar 4 | Oct 4 – Oct 19 |
| Pea | Hardy | — | Jan 1 – Jan 3 | Feb 25 – Mar 12 | Sep 24 – Oct 9 |
| Spinach | Hardy | — | Jan 1 – Jan 3 | Feb 10 – Feb 20 | Oct 14 – Oct 24 |
| Carrot | Half-hardy | — | Jan 10 – Jan 17 | Mar 11 – Mar 31 | Sep 14 – Oct 4 |
| Broccoli | Half-hardy | Jan 1 | Jan 3 – Jan 17 | Feb 27 – Mar 19 | Sep 19 – Oct 9 |
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 USC00417622. 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 | Feb 22 | Mar 14 | Dec 1 | Dec 28 | 285 |
| 32°F (freeze) | Jan 31 | Mar 4 | Dec 17 | Jan 20 | 321 |
| 28°F | Jan 12 | Feb 20 | Dec 29 | Feb 1 | 357 |
| 24°F | Jan 3 | Feb 8 | Jan 1 | Feb 1 | 365 |
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) | 8,984 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 12,566 | cool-season crops (brassicas, greens) |
Hardiness zone 10a
Sullivan sits in USDA plant hardiness zone 10a on the 2023 map — meaning its average annual extreme minimum winter temperature is about 30 to 35 °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 10a, or see all USDA hardiness zones.
Frequently asked questions
- What USDA hardiness zone is Sullivan?
- Sullivan, Texas is in USDA plant hardiness zone 10a on the 2023 map (average annual extreme minimum temperature 30 to 35 °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 Sullivan?
- The average (median) last spring frost at 32°F is around January 31, from NOAA's 1991–2020 climate normals at the nearest reporting station. Roughly one year in ten the last frost is as late as March 4, so wait until then before setting out frost-tender plants if you want to be safe.
- When is the first fall frost in Sullivan?
- The average first fall frost at 32°F is around December 17. That leaves a growing season of about 321 days between the average last spring and first fall frosts.
- When should I start tomatoes in Sullivan?
- Start tomato seeds indoors about Jan 1 and transplant them outside about Feb 7 – Feb 14, once the danger of frost has passed. Estimated first harvest is around Apr 8 – Apr 28.
- How long is the growing season in Sullivan?
- About 321 days at the 32°F threshold (NOAA 1991–2020, median) — the span between the average last spring frost (~January 31) and the average first fall frost (~December 17). 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 USC00417622 (Rio Grande City, 19.2 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.