The Frost Window defines the season.
Last Spring Frost: April 22 ± 4 days
First Fall Frost: October 10 ± 4 days
These dates are drawn from 30-year averages for Story County, verified against the NOAA National Centers for Environmental Information. Plant outside this window, and the frost takes the seed. Plant inside, and the soil yields.
Winter turnip (Brassica rapa subsp. rapa) — the first green to break the crust.
Spring Sowing
Turnip (White Globe)
Sow IndoorsMar 1–15
Transplant OutApr 26 – May 5
ThinMay 12
HarvestJul 20 – Aug 10
Notes: Roots require loose soil. Compact clay = forked taproots. Cover with row fabric until June 15.
Radish (French Breakfast)
Sow DirectApr 22 – Jun 10
Germinate4–6 days
Harvest28 days post-sow
Notes: Succession sow weekly. Overcrowding = woody hearts.
Summer Succession
Carrot (Nantes)
Sow DirectMay 10 – Jul 1
ThinningJun 20
HarvestOct 15 – Nov 5
Kale (Red Russian)
Sow IndoorsJun 1–15
OutdoorsJul 10
First CutAug 25
OverwinterUnder straw mulch
Fall Storage
Beet (Detroit Dark Red)
Sow DirectJul 15 – Aug 10
Harvest TopsSep 1
Pull RootsBefore Oct 10
Parsnip (Harrow White)
Sow DirectMay 15 – Jun 15
Leave In-GroundNov 1 – Dec 15
Harvest FrozenJan 15 – Mar 1
Notes: Frost converts starch to sugar. Digging before freeze = bitter parsnips.
The Protocol
This calendar is not suggestion. It is law for Storm Lake. Each date accounts for:
- Soil temperature reaching 50°F (spring sowing threshold)
- Night length dropping below 14 hours (bolting trigger for brassicas)
- Frost probability curves from NOAA NCDC historical records
- Storage humidity requirements for root vegetables (90–95% RH)
Source: NOAA National Centers for Environmental Information — Storm Lake Airport Station (USW00094177)