St. Mary County, in Louisiana, sits in USDA hardiness zone 9b — enough range to grow cool-season vegetables, hardy fruit, and warm-season crops that mature before the first hard frost.
Crops well matched to these conditions include satsuma orange, okra, pecan, and muscadine grape — though what thrives on any one site still turns on its specific soil, sun, and drainage.
St. Mary County lies within the Gulf Coast and the Mississippi Delta — a regional growing area with its own character.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring
St. Mary County holds more than one microclimate.
Soils and elevations shift across St. Mary County, so your frost dates and drainage aren't the county average. Enter your address and we'll score 1,112 plants against your land's actual soil, sun, and frost.
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
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Quick Facts
USDA Zones
9b
Last Frost (state avg.)
Feb 15 - Mar 15
First Frost (state avg.)
Nov 10 - Dec 10
County Area
357K acres
Hardiness Zone Range
Growing Season
Zone maps are averages across St. Mary County. Your yard's slope, trees, and frost pockets shift what actually grows — see your land's exact reading.
Soil in St. Mary County
Across St. Mary County, the ground is predominantly Histosols, where Maurepas, Baldwin, and Kenner are the most extensive named soil series. The soil is generally very poorly drained with a clay surface. Topsoil pH runs about 6.0–6.7, slightly acidic. Rainfall drains through hydrologic group D soils.
Soil order
Histosols
Drainage
Very poorly drained
Prime farmland
27%
Hydric soils
92%
Soil still varies lot by lot — soil types explained.
What Grows in St. Mary County
Plants matched to St. Mary County's USDA zones 9b — each links to its full growing profile.
Growing Challenges in Louisiana
What an experienced grower plans around here — each one has a move.
Extreme humidity and rainfall promote rot and fungal diseases
Raised rows, morning base-watering, and generous spacing keep the wet at bay — extension's resistant-variety lists do the rest.
Poor drainage in delta and coastal areas
Where ground stays wet, grow up — mounded rows and raised beds keep roots breathing through the wettest months.
Hurricane damage risk from June through November
Wind-tough perennials, proper staking, and fall crops in movable containers take the sting out of storm season.
For cultivar selection, pest pressure, and planting-time guidance specific to Louisiana, the LSU AgCenter is the authoritative local source.
Safe to Grow Here?
What the federal record shows across St. Mary County — and how to grow with it.
We checked the federal record across St. Mary County — 718 documented sites across 5 of the 9 source types we track.
The most significant on record: 34 Toxics Release Inventory facilities. Active industrial facilities reporting chemical releases to air, water, and land.
There's a meaningful federal record across St. Mary County — worth a look before you plant food, not a reason to hold back from growing. Proximity to a documented site is information, not a diagnosis of any one yard. A soil test before new food beds is the sensible precaution here, and the map shows exactly which sites sit where, so you can see what's actually near you.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
Environmental Intelligence
Understanding what's nearby helps you make informed decisions about where and how to grow.
Total Sites
718
across St. Mary County
Risk Level
Elevated
Highest-severity
34 Toxics Release Inventory facilities
Sources Checked
across St. Mary County
Severity Distribution
across St. Mary County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around St. Mary County, two things run higher than the national average — PFAS (7 sites) and Brownfields (389 sites). Knowing it is half the work — and it's nothing a thoughtful grower can't plan for.
PFAS: PFAS (per- and polyfluoroalkyl substances) are called "forever chemicals" because they do not biodegrade.
Brownfields: Brownfield sites are former commercial or industrial properties where legacy soil contamination (heavy metals, PAHs, petroleum compounds) may persist.
Test irrigation water source — this is the primary pathway for PFAS to reach garden crops.
Check EPA brownfield remediation status — many sites have completed cleanup with institutional controls.
Check your specific parcel in St. Mary County
Get exact proximity distances to contamination sources for your specific parcel — plus soil, sun, drainage, and 1,112 plant recommendations.
Three things about your exact spot that zone averages miss:
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources analyzed in seconds
Your Specific Parcel Matters
St. Mary County Average
- ●USDA Zones 9b
- ●Generic soil type for the area
- ●State-average frost dates
YOUR Parcel
- ✓Your exact hardiness zone
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in St. Mary County
Pull a site-specific report for your exact address in St. Mary County, Louisiana — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your exact spot that zone averages miss:
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources analyzed in seconds
Key Growing Facts for St. Mary County, Louisiana
- USDA Hardiness Zones: 9b (USDA PHZM 2023)
- Last Spring Frost (state avg.): Feb 15 - Mar 15 (NOAA 30-Year Climate Normals)
- First Fall Frost (state avg.): Nov 10 - Dec 10 (NOAA 30-Year Climate Normals)
- County Land Area: 357K acres (US Census TIGER 2025)
Zone data: USDA ARS Plant Hardiness Zone Map 2023. Climate data: NOAA NCEI. County boundaries: US Census TIGER/Line 2025.
Frost dates here are the St. Mary County average. Low spots and tree cover move them by days on any one yard — see your exact frost windows.
Frequently Asked Questions
What hardiness zone is St. Mary County, Louisiana?
St. Mary County sits in USDA hardiness zone 9b, per the USDA Plant Hardiness Zone Map 2023. Zones reflect average annual extreme minimum temperatures from 1991–2020 weather data.
When does frost risk typically end in St. Mary County?
St. Mary County follows Louisiana's statewide frost window: last spring frost around Feb 15 - Mar 15 and first fall frost around Nov 10 - Dec 10, per NOAA 30-year climate normals (1991–2020). Frost dates shift with elevation and local microclimate, so watch your own site's cold pockets.
What vegetables grow in St. Mary County?
St. Mary County's zone 9b supports a wide range — strong performers include Satsuma Orange, Okra, Pecan, Muscadine Grape, and Live Oak. 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.
Which hardiness zone is St. Mary County, really?
Officially, St. Mary County sits in USDA zone 9b (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.
Is the soil safe to grow vegetables in St. Mary County?
The federal record around St. Mary County is a meaningful one — 718 documented sites — 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.
Just moved to St. Mary County — what should I know before planting?
Start with three facts. St. Mary County sits in USDA zone 9b, which sets what survives winter; the statewide frost window runs about Feb 15 - Mar 15 to Nov 10 - Dec 10 (NOAA 30-year climate normals); and 718 documented sites sit on the federal record here, so a soil test before food beds is the smart first step. From there, matching plants to your actual soil and sun is the fun part.
Everything on this page is a St. Mary County average. Your yard writes its own version — 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 Louisiana's frost window, season length, and soil profile against the plant's real requirements.