The frost date in Story County falls on October 15th, give or take three days depending on the chinook winds off the Missouri. This guide does not teach hope. It teaches timing.
Each section below names a root crop that survives the freeze, lists the exact window for sowing, and marks the depth at which the taproot finds shelter. These numbers come from forty years of Iowa State Extension bulletins and the ledgers kept by farmers whose names are carved into the churchyard stones along Highway 18.
WINTER TURNIP (Brassica rapa var. rapa)
HARVEST PROTOCOL
Lift before the first hard freeze (−12°C). Store in sand at 0°C with 95% humidity. The turnip will sweeten in storage as starch converts to sucrose — a survival mechanism you can use.
HEIRLOOM CARROT (Daucus carota subs. sativus)
HARVEST PROTOCOL
Leave in ground under heavy straw mulch. Harvest through January as needed. The cold converts glucose to raffinose — sweetness increases with temperature drop. Pull only what you will use within 48 hours.
PARSNIP (Pastinaca sativa)
HARVEST PROTOCOL
Do not harvest before November 1. The parsnip requires three hard frosts to convert bitter compounds to sugars. Mark the row — you will dig in February.