When to plant in Union, MO
USDA Zone 6bHere are the average frost dates, USDA hardiness zone, and a month-by-month planting calendar for Union, Missouri — all computed from Union's nearest NOAA weather station.
In zone 6b, Union gardeners can grow many hardy perennials, while the last and first frost still dictate the annual vegetable calendar.
The average last spring frost in Union is now 5 days earlier than in the 1981–2010 normals. See how frost dates are shifting nationwide →
Frost probability
UNION · 1991–2020The date the last spring and first fall frost occur, by threshold and probability. A 90% date is later in spring — and earlier in fall — than a 10% date; the 50% · 32°F row is what most gardeners plan around. These are Union’s own odds, recorded at UNION.
| Threshold | SPRING 10% | SPRING 50% | SPRING 90% | FALL 10% | FALL 50% | FALL 90% |
|---|---|---|---|---|---|---|
| 36°F | May 8 | Apr 22 | Apr 8 | Sep 30 | Oct 13 | Oct 26 |
| 32°F | Apr 28 | Apr 11 | Mar 26 | Oct 9 | Oct 23 | Nov 5 |
| 28°F | Apr 15 | Mar 31 | Mar 12 | Oct 21 | Nov 3 | Nov 18 |
Download this table as CSV ↓ — every threshold and probability, plus this city’s planting-window dates.
What to plant now
TODAY · JULY 19Full-year planting calendar
Each bar is the exact window to take a planting action in Union, drawn to the day from the local frost dates. The dashed line is today.
Nearby weather stations
3 within 33 km · complete 32°F normalsWhen stations disagree by more than a few days, that spread is real microclimate variation — elevation, water, urban heat. Judge which station best matches your own yard.
Union planting FAQ
When is the last spring frost in Union, MO?
Plan for the last spring frost in Union around April 11 (the date it has a 50% chance of a 32°F freeze). Anything frost-sensitive should go out after it.
When is the first fall frost in Union, MO?
In Union, the first 32°F freeze of fall lands around October 23 on average. Time your last harvests and any season-extension cover before it.
What hardiness zone is Union in?
Union is in USDA hardiness zone 6b. In zone 6b, winters are moderate — most common vegetables grow well in season.
How long is the growing season in Union?
Union has about 195 frost-free days — a moderate growing season — between the average last spring frost (April 11) and first fall frost (October 23).
When should I plant tomatoes in Union?
For Union, sow tomatoes indoors about February 14–February 28 and move the seedlings out around April 18, after the last spring frost.
Never miss a window in Union
An email when it’s time to start seeds, transplant, and sow — timed to Union’s frost dates. Double opt-in, one-click unsubscribe, no spam.
Nearby cities
8 within reach- Washington · 13 km
- Eureka · 31 km
- Wildwood · 32 km
- Ellisville · 39 km
- Dardenne Prairie · 42 km
- Lake St. Louis · 42 km
- Ballwin · 43 km
- Wentzville · 43 km
Frost dates recorded at UNION, 1 km from the city center · 1991–2020 NOAA climate normals · zone from the USDA/PRISM 2023 map. How we compute this.
BlissGarden. "When to Plant in Union, MO — Frost Dates & Zone 6b." Frost normals: NOAA NCEI U.S. Climate Normals 1991–2020, station USC00238515. Retrieved from https://blissgarden.com/missouri/union.