When to plant in Johnston, IA
USDA Zone 5bHere are the average frost dates, USDA hardiness zone, and a month-by-month planting calendar for Johnston, Iowa — all computed from Johnston's nearest NOAA weather station.
In zone 5b, Johnston gardeners can grow many hardy perennials, while the last and first frost still dictate the annual vegetable calendar.
Frost probability
DES MOINES WSFO-JOHNSTON · 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 Johnston’s own odds, recorded at DES MOINES WSFO-JOHNSTON.
| Threshold | SPRING 10% | SPRING 50% | SPRING 90% | FALL 10% | FALL 50% | FALL 90% |
|---|---|---|---|---|---|---|
| 36°F | May 13 | Apr 30 | Apr 15 | Sep 23 | Oct 7 | Oct 21 |
| 32°F | May 3 | Apr 19 | Apr 5 | Oct 1 | Oct 18 | Oct 30 |
| 28°F | Apr 23 | Apr 9 | Mar 25 | Oct 14 | Oct 27 | Nov 9 |
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 Johnston, drawn to the day from the local frost dates. The dashed line is today.
Nearby weather stations
3 within 19 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.
Johnston planting FAQ
When is the last spring frost in Johnston, IA?
On average, the last spring frost in Johnston is around April 19 (50% probability at 32°F, from 1991–2020 NOAA normals). Wait until after this date to set out tender plants like tomatoes and peppers.
When is the first fall frost in Johnston, IA?
In Johnston, the first 32°F freeze of fall lands around October 18 on average. Time your last harvests and any season-extension cover before it.
What hardiness zone is Johnston in?
Johnston is in USDA hardiness zone 5b. In zone 5b, winters are cold — pick cold-hardy varieties and protect tender crops.
How long is the growing season in Johnston?
Johnston has about 182 frost-free days — a moderate growing season — between the average last spring frost (April 19) and first fall frost (October 18).
When should I plant tomatoes in Johnston?
For Johnston, sow tomatoes indoors about February 22–March 8 and move the seedlings out around April 26, after the last spring frost.
Never miss a window in Johnston
An email when it’s time to start seeds, transplant, and sow — timed to Johnston’s frost dates. Double opt-in, one-click unsubscribe, no spam.
Nearby cities
8 within reach- Grimes · 7 km
- Urbandale · 8 km
- Clive · 11 km
- Ankeny · 11 km
- Des Moines · 16 km
- West Des Moines · 16 km
- Waukee · 17 km
- Altoona · 21 km
Frost dates recorded at DES MOINES WSFO-JOHNSTON, 5 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 Johnston, IA — Frost Dates & Zone 5b." Frost normals: NOAA NCEI U.S. Climate Normals 1991–2020, station USC00132209. Retrieved from https://blissgarden.com/iowa/johnston.