Castle Hills, Texas, sits in USDA hardiness zone 9a — a band that supports both cool-season staples and warm-season crops chosen to fit the local frost window.
A short list that earns its place here — artichoke, fig, california poppy, and cabbage — with any one site's soil, sun, and drainage making the final cut.
Even in Castle Hills, no two yards are alike.
A low spot, a south-facing slope, or a stand of trees moves the frost date and sun across a single Castle Hills lot. 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 Castle Hills — soil, climate, flood, and parcel records. How we handle your address.
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Castle Hills — the short answer
Castle Hills, Texas: USDA zone 9a, about 306 days between hard freezes, across 2K acres of city.
- USDA zone
- 9a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Feb 6
- Bexar County normal — NOAA 1991–2020, nearest to this town
- First hard freeze (28°F)
- Dec 9
- Bexar County normal — NOAA 1991–2020, nearest to this town
- Days between freezes
- ~306
- Bexar County normal — NOAA 1991–2020, nearest to this town
- City area
- 2K acres
- US Census TIGER/Line 2025
Every figure names the dataset it came from. No 30-year normal resolves at this town’s own centroid, so the hard-freeze dates are Bexar County’s — the closest measured record, labelled as such rather than passed off as local.
Hardiness Zone Range
Zone 9a is Castle Hills's average, not your lot's — a low corner or a tree line moves it. Against Castle Hills's 306-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Castle Hills
Each reading below is measured for Castle Hills itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
From county recordsCastle Hills runs about 306 days between hard freezes (read from Bexar County, the closest normal to Castle Hills) — close to year-round growing.
Frost is rarely the limit here; winter plantings are as real as summer ones, and the harder question is which crops shrug off the summer heat.
Grow cool-season crops through the mild winter, and choose heat-tolerant varieties for the summer beds.
NOAA 1991–2020 Climate Normals
Winter hardiness
MeasuredCastle Hills sits in USDA hardiness zone 9a.
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 Castle Hills is in
Castle Hills sits in the Texas Blackland Prairies — EPA Level III, inside the wider Great Plains. That is read at Castle Hills's own centroid rather than borrowed from Bexar County.
What Grows in Castle Hills
Every plant below cleared Castle Hills's own zone 9a and its 306-day season. Each card opens that plant's Texas profile. How we score.
Is it too late to plant in Castle Hills?
Almost never — the real question is what to plant next. Cool-season crops can go in from around Jan 9; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Feb 6 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Dec 9 — long-season crops need about 90 days of runway, quick greens only 30. In a climate this gentle, “too late” hardly applies — the question becomes which crops prefer the cooler months ahead.
Documented around Castle Hills
Survey cells within 31 miles of Castle Hills checked for spotted lanternfly, none carrying a detection — a surveyed negative, not an absence of looking. Nearest documented record 667 miles off. What to watch for.
What's on the federal record near Castle Hills
Closest first, within ~10 miles of Castle Hills. Listing isn't leaking, and distance isn't exposure.
- AY-68-28-905Nitrate · 800 ft
- DIAMOND SHAMROCK 0305Underground Storage Tanks · 1900 ft
- FUEL STATION 4Underground Storage Tanks · 2100 ft
- DAVID SANFORDS GULF SERVICEUnderground Storage Tanks · 0.5 mi
- SAN ANTONIO DIAMOND 342 CENTRAL OFFICEUnderground Storage Tanks · 0.5 mi
- AY-68-28-919Nitrate · 0.6 mi
- CITY OF CASTLE HILLSUnderground Storage Tanks · 0.6 mi
- CVS PHARMACY 7306Brownfields · 0.6 mi
- AY-68-28-904Nitrate · 0.6 mi
- FIRESTONE SERVICE CENTERUnderground Storage Tanks · 0.7 mi
- HEB 389Underground Storage Tanks · 0.7 mi
- SMILE FOOD MART 2Underground Storage Tanks · 0.8 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Castle Hills'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 Castle Hills.
Total Sites
2,943
within ~10 miles of Castle Hills
Risk Level
Elevated
Highest-severity
11 Superfund sites
Sources Checked
within ~10 miles of Castle Hills
Severity Distribution
within ~10 miles of Castle Hills
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Castle Hills, Underground Storage Tanks runs higher than the national average — 2,028 sites within ~10 miles of Castle Hills. That's not a problem with your land — it's information about it.
Underground Storage Tanks: Underground storage tanks are the single most common source of soil contamination near homes and gardens.
Use raised beds with imported soil — this eliminates the primary soil-contact pathway.
Check your specific parcel in Castle Hills
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 Castle Hills average
Your land is one point inside Castle Hills
Everything above resolves to Castle Hills as a whole — one PHZM band, read across 2K acres, with hard-freeze dates borrowed from Bexar County’s record because no 30-year normal resolves at this city’s own centroid. 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 city 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 local average.
Your Lot vs the Castle Hills Average
Castle Hills Average
- ●USDA Zones 9a, averaged across Castle Hills
- ●One soil character for all of Castle Hills
- ●Frost dates read at Castle Hills's scale: Feb 6 to Dec 9
YOUR Parcel
- ✓Your exact zone, not Castle Hills's 9a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Castle Hills
Pull a site-specific report for your exact address in Castle Hills, Texas — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Castle Hills averages can't show:
We read public map data around Castle Hills — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Castle Hills average
How we know this about Castle Hills
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at this city’s own centroid; hard-freeze dates from NOAA 1991–2020 28°F normals at Bexar County’s record, because none resolves here; boundaries and acreage from US Census TIGER/Line 2025; the contamination records from the federal sources named in their beats above. Soil is not read at city grain anywhere on this page — there is no city-resolution survey in our data, which is why you will find no soil grid here rather than a statewide one wearing a local label. The resolution ledger below names every figure this page inherited.
Common questions about Castle Hills
When does frost risk typically end in Castle Hills?
The last hard freeze (28°F) in Castle Hills typically lands around Feb 6, 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 Feb 27.
When is the first frost in Castle Hills?
The first hard freeze (28°F) in Castle Hills typically arrives around Dec 9, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Nov 25, so the watching starts about Nov 9 — about 306 days after the spring freeze cleared.
How long is the growing season in Castle Hills?
Measured between 28°F hard freezes, Castle Hills sees about 306 frost-free days — roughly Feb 6 through Dec 9, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Feb 27 to Nov 25, about 271 days.
Is the soil safe to grow vegetables in Castle Hills?
The federal record around Castle Hills is a meaningful one — 2,943 documented sites, mostly Underground Storage Tanks entries (2,028), the nearest Nitrate record about 0.2 miles out — so a soil test before new food beds is a sensible precaution here, not a reason to hold back from growing. Remember that proximity to a documented site is information, not a diagnosis of any one yard; the contamination map shows exactly what sits where.
How do I protect my plants from frost in Castle Hills?
From about Nov 9 the job here turns from planting to protecting — the last start even a 30-day crop can finish. As the season closes around the first 28°F hard freeze near Dec 9 (NOAA 1991–2020 climate normals), three moves buy time: row cover or an old sheet over tender plants on still, clear nights; water the soil the afternoon before a freeze, so it holds warmth overnight; and harvest tomatoes, peppers and basil before Dec 9. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Castle Hills's scale — its 9a band and its 306-day season. Your yard writes its own version of Castle Hills's numbers: we read soil, sun, drainage and frost at your exact address. Try it for 14 days — no card required.
What this page reads at Castle Hills’s own scale
6 of the readings below were taken at Castle Hills's own scale — the 1,580 acres it covers and 2,943 documented sites around it; 5 are borrowed from a wider read, named and linked below.
Measured here
- Castle Hills's own USDA hardiness band, zones 9aUSDA PHZM 2023
- 2,943 documented contamination sites on the federal record near Castle Hills, the closest Nitrate record about 0.2 miles out from the town centreFederal environmental registers
- Castle Hills's boundary and the 1,580 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 9a and a ~306-day seasonGrowable Ground crop-matching engine
- The ecoregion at Castle Hills's own centroid, the Texas Blackland PrairiesUS EPA Level III Ecoregions
- Lanternfly survey cells around Castle Hills checked, none carrying a detectionlydemapr (De Bona & Helmus), 10 km survey lattice
Inherited from a wider read
- The 28°F hard-freeze dates — Castle Hills has no normal of its own, so its county's is the closest measured readfrom Bexar County
- Soil character — no town-scale survey exists, so Castle Hills's 1,580 acres read through its county's SSURGO summaryfrom Bexar County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Bexar County
- The growing challenges every Texas grower plans around — written at state scale, so they stay on the state guidefrom Texas
- Butterfly and beetle records, and the farmland pesticide estimate — all published county-widefrom Bexar County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Castle Hills's 1,580 acreswhy one lot differs from the next →
- Which side of Castle Hills you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 1,580 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Nitrate record about 0.2 miles out, measured from the town centrehow we read the record →
- Where cold air settles, which slopes face the sun, and which way the wind runs on your own ground — measured at your address, and averaged away by any Castle Hills-wide figureread your own land →
More in Texas
Wider growing context
What grows across TexasCastle Hills sits outside our named growing regions, so Texas as a whole is its closest context here.
Nearby growing guides