What Grows in Knox County, Missouri

Knox County sits in USDA hardiness zone 6a, per the USDA Plant Hardiness Zone Map 2023. Zones reflect average annual extreme minimum temperatures from 1991–2020 weather data.

Almost never — the real question is what to plant next. Cool-season crops can go in from around Feb 20; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Mar 20 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Nov 16 — long-season crops need about 90 days of runway, quick greens only 30. With a season this long, “too late” mostly means “switch crops” — second sowings and a full fall garden are the norm, with garlic closing the year.

The last hard freeze (28°F) in Knox County typically lands around Mar 20, per NOAA 1991–2020 climate normals — an earlier marker than the light-frost dates many planting charts quote. That marks the hard freeze, not the last light frost — light frosts can still bite for a few more weeks, so tender transplants usually wait another 2–3 weeks.

Measured between 28°F hard freezes, Knox County sees about 241 frost-free days — roughly Mar 20 through Nov 16, per NOAA 1991–2020 climate normals. Tender crops get a somewhat shorter practical window, since lighter frosts reach a few weeks past the hard-freeze dates on both ends.

Knox County's zone 6a supports a wide range — strong performers include Tomato, Peach, Grape, Dogwood, and Blackberry. What actually takes on any one site comes down to its soil, sun, and drainage, and we score each plant against the real conditions at your address.

Officially, Knox County sits in USDA zone 6a (USDA PHZM 2023) — but a zone is a 30-year average of winter's coldest night across an area, and it can't see any one yard. A south-facing slope, a tree line, or a low frost pocket can shift a single site by half a zone either way, which is why neighboring gardeners often quote different numbers. We read the conditions at your exact address — soil, sun, slope, and frost — and score 1,112 plants against what's actually there.

The federal record around Knox County shows 31 documented sites — a typical footprint for a growing area, and proximity to a documented site is information, not a diagnosis of any one yard. It's worth seeing which recorded sites sit closest to where you grow, and testing the soil before new food beds near any of them.

Start with three facts. Knox County sits in USDA zone 6a, which sets what survives winter; the last 28°F hard freeze typically clears around Mar 20, with about 241 frost-free days to work with (NOAA 1991–2020 climate normals); and 31 documented sites sit on the federal record — a typical footprint for a growing area, worth a look on the contamination map before food beds. From there, matching plants to your actual soil and sun is the fun part.