Knox County, in Texas, sits in USDA hardiness zone 8a — a range where zone-matched perennials and frost-aware annual timing set what succeeds.
A short list that earns its place here — cabbage, fig, california poppy, and collard greens — with any one site's soil, sun, and drainage making the final cut.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Knox County holds more than one microclimate.
Soils and elevations shift across Knox County, so your frost dates and drainage aren't the county average. Enter your address and we'll score 1,086 plants against your land's actual soil, sun, and frost.
We read public map data around Knox County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Knox County — the short answer
Knox County, Texas: USDA zone 8a, about 257 days between hard freezes, across 544K acres.
- USDA zone
- 8a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Mar 9
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Nov 21
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~257
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 544K acres
- US Census TIGER/Line 2025
Every figure names the dataset it came from. Hard-freeze dates are county 28°F normals: light frosts run a few weeks past them, and tender transplants usually wait 2–3 weeks after the last hard freeze.
Hardiness Zone Range
Zone 8a is Knox County's average, not your lot's — a low corner or a tree line moves it. Against Knox County's 257-day season, see what your own ground reads.
Heat and winter chill in Knox County
Across a year, Knox County accumulates about 5,666 growing degree days above 50°F, about 158 fewer than the middle Texas county — ahead of 99 of Texas’s 254 counties. Degree days are the heat a crop actually gets to work with — more of them is more room to ripen a long-season crop before the freeze closes the window.
Winter banks about 1,513 hours below 45°F, 418 more than the Texas middle of 1,095. Chill is what tells a fruit tree its dormancy is over, and it is set by climate rather than by anything you can build.
Grounded in PRISM Climate Group, Oregon State University — 1991–2020 monthly normals
Soil in Knox County
Across Knox County, the ground is predominantly Alfisols, where Knoco, Miles, and Tillman are the most extensive named soil series. The soil is generally well drained with a clay surface. Topsoil pH runs about 7.0–8.2, slightly alkaline. Rainfall drains through hydrologic group D soils.
Soil order
Alfisols
Drainage
Well drained
Prime farmland
31%
Hydric soils
0%
Soil still varies lot by lot — soil types explained.
How the ground varies across Knox County
The USDA soil survey maps 96% of Knox County as well drained — but another 3% drains differently: 3% somewhat excessively drained.
Knoco is the most extensive named soil at 16% of mapped acres, then Miles (13%) and Tillman (7%).
Which of them your own lot sits on is a parcel question, not a county one. Check your address for the survey at your boundary.
What this means for growing in Knox County
Each reading below is measured for Knox County itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Drainage
MeasuredThe dominant soils across Knox County are well drained, in hydrologic group D — ground that drains quickly.
The upside is soil you can work early in spring and roots that never drown; the cost is that fast-draining ground dries out fast and leaches nutrients away before plants can use them.
Work in compost and mulch to hold moisture and feed, and water more often in short doses than deep and rarely.
USDA NRCS SSURGO
Surface pH
MeasuredTopsoil across Knox County runs about pH 7.0–8.2, on the alkaline side.
Many vegetables cope, but acid-lovers like blueberries struggle, and iron and manganese lock up above about pH 7.5 — leaves yellow between the veins even in rich soil.
Elemental sulfur and generous organic matter lower pH slowly for the beds that need it; test first so you add only what the soil actually calls for.
USDA NRCS SSURGO
Season length
MeasuredKnox County runs about 257 days between hard freezes — a long growing season.
There is slack for succession plantings and slow-finishing crops: many vegetables can be sown twice, and the heat-lovers have time to ripen fully.
Plan a second sowing of quick crops after the first comes out, and use the fall window most gardeners let sit idle.
NOAA 1991–2020 Climate Normals
Winter hardiness
MeasuredKnox County sits in USDA hardiness zone 8a.
The zone sets which perennials, shrubs, and fruit trees live through an average winter here — a plant rated for a colder zone is a safe bet, one rated warmer needs winter protection or gets treated as an annual.
Match perennials and fruit to the zone before you buy, so nothing you plant is a gamble against the cold.
USDA PHZM 2023
The kind of country Knox County is in
Knox County spans 2 EPA Level III ecoregions — Southwestern Tablelands (66%) and Central Great Plains (34%). Which one your land falls in changes what grows wild there and how the ground behaves, and a county-wide answer cannot tell you which.
What Grows in Knox County
We scored all 1,086 plants against Knox County's own USDA zone 8a and its own 257-day season between hard freezes, using the same matching engine that runs a full parcel report. These cleared both. Sun, soil pH and drainage vary lot by lot — those are the parcel questions below. Each card opens that plant's Texas profile.
Is it too late to plant in Knox County?
Almost never — the real question is what to plant next. Cool-season crops can go in from around Feb 9; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Mar 9 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Nov 21 — 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.
What gets applied to farmland in Knox County
USGS estimates 175,971 lb of Glyphosate on Knox County farmland in 2019, its largest by weight, ahead of 2,4-d (21,624 lb) and Dicamba (14,937 lb).
Farmland across the whole county, not any one lot. Check your address for the site-by-site record.
Safe to Grow Here?
What the federal record shows across Knox County — and how to grow with it.
We checked the federal record across Knox County — 94 documented sites across 4 of the 9 source types we track.
The most significant on record: 12 mining sites. Historic and active mines that may leach heavy metals like arsenic, lead, and cadmium.
The federal record across Knox County is a modest one — a typical footprint for a growing area. Nothing here calls for alarm; it's worth knowing which recorded sites sit closest to where you grow, and each one on the map carries its type and location. If one turns out to be a near neighbor, a one-time soil test settles the question.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
What's on the federal record near Knox County
Closest first, across Knox County. Listing isn't leaking, and distance isn't exposure.
- MOORHOUSE GARAGEUnderground Storage Tanks · 0.7 mi
- AIR AGUnderground Storage Tanks · 0.7 mi
- D & H AERIALUnderground Storage Tanks · 0.7 mi
- KC OIL 2Underground Storage Tanks · 0.7 mi
- ALLSUPS 193Underground Storage Tanks · 0.7 mi
- COOK GAS SERVICEUnderground Storage Tanks · 0.7 mi
- JAMES PEEK EXXONUnderground Storage Tanks · 0.7 mi
- JAMES N SMITHUnderground Storage Tanks · 0.7 mi
- TWO RIVERS FARM SUPPLYUnderground Storage Tanks · 0.7 mi
- BENJAMIN EXXONUnderground Storage Tanks · 0.7 mi
- TERRA INTERNATIONALUnderground Storage Tanks · 0.7 mi
- FARMERS GRAIN COOPERATIVE OF MUNDAYUnderground Storage Tanks · 0.7 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Knox County's center, not your beds. Run your own address for what's upwind of you specifically.
Environmental Intelligence
The counts behind that headline — every source type on the record near Knox County.
Sources Checked
across Knox County
Severity Distribution
across Knox County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Knox County, two things run higher than the national average across Knox County — Mining (12 sites) and Nitrate (42 sites). Knowing it is half the work — and it's nothing a thoughtful grower can't plan for.
Mining: Mining sites — both historic and active — can leach heavy metals (arsenic, lead, cadmium, mercury) into soil and water for centuries after operations cease.
Nitrate: Nitrate contamination primarily comes from agricultural fertilizer runoff and failing septic systems.
Test soil for heavy metals (lead, arsenic, cadmium, mercury) — this is essential near any mining site.
Test well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Check your specific parcel in Knox County
Get exact proximity distances to contamination sources for your specific parcel — plus soil, sun, drainage, and 1,086 plant recommendations.
25+ data sources read at your address, not the Knox County average
Your land is one point inside Knox County
Everything above resolves to Knox County as a whole — one PHZM band and one county frost record, read across 544K acres. Your parcel is one point inside that footprint. Slope, tree cover, a low spot that pools cold air, and what is in the soil are all resolved at the address, and none of them are visible at county scale. That is the honest boundary of this page, and the reason the next step is a reading of your own ground rather than a better county average.
Your Lot vs the Knox County Average
Knox County Average
- ●USDA Zones 8a, averaged across Knox County
- ●One soil character for all of Knox County
- ●Frost dates read at Knox County's scale: Mar 9 to Nov 21
YOUR Parcel
- ✓Your exact zone, not Knox County's 8a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Knox County
Pull a site-specific report for your exact address in Knox County, Texas — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Knox County averages can't show:
We read public map data around Knox County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Knox County average
How we know this about Knox County
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at county grain; hard-freeze dates from NOAA 1991–2020 28°F normals at this county’s own record where one resolves, and the labelled statewide window where none does; soils from the USDA NRCS SSURGO survey, area-weighted across the county’s own map units; boundaries and acreage from US Census TIGER/Line 2025; the contamination and pesticide records from the federal sources named in their beats above. Where Knox County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Knox County
When does frost risk typically end in Knox County?
The last hard freeze (28°F) in Knox County typically lands around Mar 9, per NOAA 1991–2020 climate normals — earlier than the light-frost dates most charts quote. That marks the hard freeze, not the last light frost — lighter frosts keep biting past it, which is why tender transplants here wait until about Mar 30.
How long is the growing season in Knox County?
Measured between 28°F hard freezes, Knox County sees about 257 frost-free days — roughly Mar 9 through Nov 21, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Mar 30 to Nov 7, about 222 days.
Is the soil safe to grow vegetables in Knox County?
The federal record around Knox County shows 94 documented sites, mostly Nitrate entries (42), the nearest Underground Storage Tanks record about 0.7 miles out — 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.
Everything above is measured at Knox County's scale — its 8a band and its 257-day season. Your yard writes its own version of Knox County's numbers: we read soil, sun, drainage and frost at your exact address. Try it for 14 days — no card required.
Will It Grow Here?
Zone fit is the first question — each answer below reads Texas's frost window, season length, and soil profile against the plant's real requirements.
What this page reads at Knox County’s own scale
8 of the readings below were taken at Knox County's own scale — its own ~257-day span between 28°F freezes, the 3 most extensive soil series mapped here and 94 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Knox County's own USDA hardiness band, zones 8aUSDA PHZM 2023
- Knox County's own 28°F hard-freeze dates and its ~257-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Knox CountyUSDA NRCS SSURGO
- 94 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Underground Storage Tanks record about 0.7 miles outFederal environmental registers
- Knox County's boundary and the 544,397 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 8a and a ~257-day seasonGrowable Ground crop-matching engine
- The 2 ecoregions Knox County spans, Southwestern Tablelands the largestUS EPA Level III Ecoregions
- Which agricultural compounds go onto Knox County farmland, and roughly how muchUSGS NAWQA EPest county estimates
Inherited from a wider read
- The growing challenges every Texas grower plans around — written at state scale, so they stay on the state guidefrom Texas
What this page can’t tell you
- How the season shifts across Knox County — the ~257 days above is one reading at its centre; the 12 towns below each carry their owntowns in this county →
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Knox County's 544,397 acreswhy one lot differs from the next →
- Which of those 94 documented sites actually reaches your soil — that needs your address, the wind, and the groundwater directionhow we read the record →
- Where cold air settles, which slopes face the sun, and which way the wind runs on your own ground — none of it survives being averaged over Knox Countyread your own land →