Frost dates for 63021Ballwin, MO
The average last spring frost in Ballwin is April 4 and the average first fall frost is October 29, giving a typical growing season of about 206 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Apr 4
- Average first fall frost
- Oct 29
- Growing season
- 206 days
Safer after Apr 21 (1-in-10 risk)
Possible by Oct 15 (1-in-10 risk)
Last frost typically in 154 days
Frost risk by date
NOAA reports frost dates as probabilities. The middle date is the average (a 50% chance). For spring, the 10% date is a safer planting date: frost after it happens in about 1 year in 10. Light frost (36°F) can damage tender plants; a hard freeze (28°F) kills most annuals.
| Temperature | Last spring: 90% / 50% / 10% chance | First fall: 10% / 50% / 90% chance | Growing season (50%) | Years with at least one |
|---|---|---|---|---|
| Light frost (36°F) | Apr 3 · Apr 16 · May 1 | Oct 5 · Oct 19 · Oct 31 | 185 days | 100% |
| Frost / freeze (32°F) | Mar 20 · Apr 4 · Apr 21 | Oct 15 · Oct 29 · Nov 11 | 206 days | 100% |
| Hard freeze (28°F) | Mar 8 · Mar 25 · Apr 8 | Oct 27 · Nov 8 · Nov 27 | 228 days | 100% |
Planting calendar for Ballwin
Planting windows from the University of Maryland Extension calendar, shifted to your average frost dates. Use them as a starting point and adjust for seed packet instructions and local conditions.
| Crop | Task | Window |
|---|---|---|
| Tomatoes | Start seeds indoors | Mar 4 – May 10 |
| Tomatoes | Transplant outdoors | Apr 20 – Jul 9 |
| Peppers | Start seeds indoors | Mar 4 – Apr 4 |
| Peppers | Transplant outdoors | May 4 – Jun 4 |
| Eggplant | Start seeds indoors | Mar 21 – Apr 19 |
| Eggplant | Transplant outdoors | May 4 – Jun 4 |
| Cucumbers | Sow outdoors | May 4 – Jul 19 |
| Summer squash | Sow outdoors | Apr 20 – Jun 4 |
| Winter squash & pumpkins | Sow outdoors | May 4 – Jun 4 |
| Snap beans | Sow outdoors | Apr 20 – Aug 11 |
| Sweet corn | Sow outdoors | Apr 20 – Jul 9 |
| Watermelon & cantaloupe | Sow outdoors | May 4 – Jun 4 |
| Okra | Sow outdoors | Apr 27 – May 20 |
| Peas | Sow outdoors (spring) | Mar 4 – Apr 19 |
| Potatoes | Plant outdoors (spring) | Mar 4 – May 4 |
| Onions | Start seeds indoors (spring) | Jan 21 – Feb 17 |
| Onions | Transplant outdoors (spring) | Mar 21 – Apr 19 |
| Broccoli | Start seeds indoors (spring) | Feb 14 – Mar 20 |
| Broccoli | Transplant outdoors (spring) | Mar 21 – Apr 19 |
| Broccoli | Start seeds indoors (fall) | Jun 29 – Jul 9 |
| Broccoli | Transplant outdoors (fall) | Jul 29 – Aug 9 |
| Cabbage | Start seeds indoors (spring) | Feb 4 – Mar 4 |
| Cabbage | Transplant outdoors (spring) | Mar 4 – Apr 4 |
| Cabbage | Start seeds indoors (fall) | Jun 19 – Jul 19 |
| Cabbage | Transplant outdoors (fall) | Jul 19 – Aug 19 |
| Leaf lettuce | Sow outdoors (spring) | Mar 4 – May 20 |
| Leaf lettuce | Sow outdoors (fall) | Jul 19 – Sep 4 |
| Spinach | Sow outdoors (spring) | Feb 25 – Apr 10 |
| Spinach | Sow outdoors (fall) | Aug 5 – Sep 9 |
| Radishes | Sow outdoors (spring) | Mar 4 – Apr 24 |
| Radishes | Sow outdoors (fall) | Jul 19 – Sep 19 |
| Kale | Sow outdoors (spring) | Mar 21 – Apr 10 |
| Kale | Sow outdoors (fall) | Jul 12 – Aug 19 |
| Carrots | Sow outdoors (spring) | Apr 4 – May 20 |
| Carrots | Sow outdoors (fall) | Jun 19 – Aug 4 |
| Garlic | Plant outdoors (fall) | Oct 19 – Nov 19 |
Where these dates come from
ZIP code 63021 is matched to the NOAA station St Charles 7 Ssw, MO, 12 km away, at 450 ft elevation (121 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| St Charles 7 Ssw, MO (used) | 450 ft | Apr 4 | Oct 29 |
| St Louis Sprt Of S L Ap, MO | 462 ft | Apr 12 | Oct 23 |
| Weldon Spring Nws, MO | 610 ft | Apr 10 | Oct 26 |
| St Peters 2 Se, MO | 575 ft | Apr 9 | Oct 26 |
Frost dates near Ballwin
- Ballwin, MO 63022 · last Apr 10, first Oct 26
- Valley Park, MO 63088 · last Apr 4, first Oct 29
- Saint Louis, MO 63131 · last Apr 4, first Oct 29
- Chesterfield, MO 63017 · last Apr 4, first Oct 29
- Grover, MO 63040 · last Apr 10, first Oct 26
- Fenton, MO 63026 · last Apr 1, first Nov 4
- Florissant, MO 63032 · last Apr 2, first Nov 4
- High Ridge, MO 63049 · last Apr 10, first Oct 26
Frequently asked questions
- When is the last frost in Ballwin, MO?
- For ZIP code 63021, the average last spring frost (32°F) is April 4, based on NOAA 1991-2020 climate normals for the St Charles 7 Ssw, MO weather station. There is a 1-in-10 chance of a frost after April 21.
- When is the first frost in Ballwin, MO?
- The average first fall frost (32°F) is October 29. There is a 1-in-10 chance of frost by October 15, so tender plants are at risk from that point on.
- How long is the growing season in 63021?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 206 days long.
- Are these frost dates a forecast?
- No. They are 30-year averages and probabilities from NOAA weather station records. Use them to plan, then watch your local forecast before planting tender crops or leaving them uncovered.