Frost Dates for Johnston, IA
In Johnston, IA, the average last spring frost is around Apr 19 and the average first fall frost around Oct 18, for a growing season of about 179 days. For frost-tender plants, wait until May 3, when the chance of frost drops to 10%.
Based on NOAA 1991–2020 records from the Des Moines Wsfo-Johnston, IA weather station, 3 miles away, elevation 959 ft. Frost can come earlier in low spots and valleys and later near cities and large lakes.
Frost probability by date
Chance of a 32°F frost after the spring date, or before the fall date.
| Chance | Last spring frost | First fall frost |
|---|---|---|
| 10% | May 3 | Oct 1 |
| 20% | Apr 29 | Oct 7 |
| 30% | Apr 25 | Oct 12 |
| 40% | Apr 22 | Oct 15 |
| 50% | Apr 19 | Oct 18 |
| 60% | Apr 16 | Oct 20 |
| 70% | Apr 13 | Oct 23 |
| 80% | Apr 9 | Oct 26 |
| 90% | Apr 5 | Oct 30 |
Light frost vs. hard freeze
Average (50%) dates for each temperature. Tender plants are damaged at 36°F; most hardy crops survive until 28°F.
| Temperature | Last in spring | First in fall |
|---|---|---|
| Light frost (36°F) | Apr 30 | Oct 7 |
| Frost / freeze (32°F) | Apr 19 | Oct 18 |
| Hard freeze (28°F) | Apr 9 | Oct 27 |
Planting calendar for Johnston
Transplant Apr 26 – May 10
Transplant May 3 – May 17
Transplant May 3 – May 17
Transplant Apr 26 – May 10
Sow or transplant Apr 26 – May 10
Sow or transplant Apr 26 – May 10
Sow or transplant May 3 – May 17
Sow or transplant Mar 22 – Apr 5
Fall sowing Aug 23 – Sep 20
Fall sowing Aug 23 – Sep 13
Fall sowing Aug 9 – Aug 23
Sow or transplant Mar 22 – Apr 5
Fall sowing Aug 9 – Sep 6
Transplant Apr 5 – Apr 19
Fall sowing Jul 26 – Aug 9
Transplant Mar 29 – Apr 12
Fall sowing Jul 26 – Aug 9
Fall sowing Jul 26 – Aug 9
Fall sowing Sep 6 – Sep 27
Fall sowing Aug 9 – Aug 23
Plant Mar 22 – Apr 5
Based on the average last frost (Apr 19) and first frost (Oct 18). The dashed lines mark those dates. Seed packets list days to maturity; adjust for your varieties.