New Castle County, in Delaware, sits in USDA hardiness zone 7b — enough range to grow cool-season vegetables, hardy fruit, and warm-season crops that mature before the first hard frost.
Expect cabbage, prickly pear, california poppy, and collard greens to be strong candidates here; the deciding factors on any one parcel stay local — soil, sun, and drainage.
New Castle County lies within the Brandywine Valley and Delmarva Peninsula — a regional growing area with its own character.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
New Castle County holds more than one microclimate.
Soils and elevations shift across New Castle 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 New Castle County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
New Castle County — the short answer
New Castle County, Delaware: USDA zone 7b, about 241 days between hard freezes, across 273K acres.
- USDA zone
- 7b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Mar 23
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Nov 19
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~241
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 273K 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 7b is New Castle County's average, not your lot's — a low corner or a tree line moves it. Against New Castle County's 241-day season, see what your own ground reads.
Heat in New Castle County
Across a year, New Castle County accumulates about 3,640 growing degree days above 50°F, about 62 fewer than the middle Delaware county — no other Delaware county banks fewer. 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.
Grounded in PRISM Climate Group, Oregon State University — 1991–2020 monthly normals
Soil in New Castle County
Across New Castle County, the ground is predominantly Ultisols, where Reybold, Glenelg, and Fallsington are the most extensive named soil series. The soil is generally well drained with a silt loam surface. Topsoil pH runs about 5.4–6.2, moderately acidic. Rainfall drains through hydrologic group B soils.
Soil order
Ultisols
Drainage
Well drained
Prime farmland
36%
Hydric soils
16%
Soil still varies lot by lot — soil types explained.
How the ground varies across New Castle County
The USDA soil survey maps 49% of New Castle County as well drained — but another 27% drains differently: 17% moderately well drained, 10% poorly drained.
Reybold is the most extensive named soil at 16% of mapped acres, then Glenelg (9%) and Fallsington (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 New Castle County
Each reading below is measured for New Castle 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 New Castle County are well drained, in hydrologic group B — 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 New Castle County runs about pH 5.4–6.2, on the acidic side.
Blueberries, potatoes, and rhododendrons thrive in it, but most vegetables start locking out nutrients below about pH 6.0 and grow pale and stunted no matter how much you feed them.
A measured lime application raises pH for the crops that need it — but test first, because the right rate depends on your own soil, not the county average.
USDA NRCS SSURGO
Wet ground
MeasuredAbout 16% of New Castle County is mapped as hydric — wetland — soil.
If your lot falls in one of those pockets, a standard in-ground bed will fight waterlogging all season, and roots that need air will struggle.
Check how your own ground drains before you dig; raised beds or moisture-loving plantings turn a wet corner from a problem into a niche.
USDA NRCS SSURGO
Season length
MeasuredNew Castle County runs about 241 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
The kind of country New Castle County is in
New Castle County spans 2 EPA Level III ecoregions — Middle Atlantic Coastal Plain (76%) and Northern Piedmont (21%). 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 New Castle County
We scored all 1,086 plants against New Castle County's own USDA zone 7b and its own 241-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 Delaware profile.
Is it too late to plant in New Castle County?
Rarely: the season closes in stages, not all at once, and each stage has its crops. Cool-season crops can go in from around Feb 23; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Mar 23 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Nov 19 — 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.
Documented around New Castle County
Spotted lanternfly documented 2 miles from New Castle County, first recorded 2019. What to watch for.
- Japanese beetle9 documented records
- monarch butterfly427 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in New Castle County
USGS estimates 58,036 lb of Glyphosate on New Castle County farmland in 2019, its largest by weight, ahead of Metolachlor & Metolachlor-s (18,282 lb) and Atrazine (18,173 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 New Castle County — and how to grow with it.
We checked the federal record across New Castle County — 3,080 documented sites across 7 of the 9 source types we track.
The most significant on record: 34 Superfund sites. Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
New Castle County carries one of the heavier federal records we track — and that's not a verdict on your yard. Proximity to a documented site is information, not a diagnosis: nothing here says any particular parcel is affected. It does earn one concrete step — before food beds go in the ground, a professional soil test tells you exactly what you're working with, and raised beds with clean imported soil grow well almost anywhere in the meantime.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
What's on the federal record near New Castle County
Closest first, across New Castle County. Listing isn't leaking, and distance isn't exposure.
- Formosa Plastics Corporation DUnderground Storage Tanks · 1800 ft
- AKZO Chemical IncUnderground Storage Tanks · 1800 ft
- Keysor CenturyUnderground Storage Tanks · 1800 ft
- AIR PRODUCTS & CHEMICALS, INC. H2 SMR PLANT AT DELAWARE CITY REFINING COMPANYToxics Release Inventory · 2100 ft
- AIR LIQUIDE INDUSTRIAL US LPToxics Release Inventory · 0.6 mi
- Bell AtlanticUnderground Storage Tanks · 0.7 mi
- FORMOSA PLASTICS CORPORATIONToxics Release Inventory · 0.7 mi
- NSTU, Inc.Underground Storage Tanks · 0.7 mi
- AIR PRODUCTS NEW CASTLE DE H2 PLANTBrownfields · 0.8 mi
- DELAWARE CITY PVC PLANTSuperfund · 0.8 mi
- EXXON RAS #20624Brownfields · 0.8 mi
- Ec22-07Nitrate · 0.8 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from New Castle 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 New Castle County.
Sources Checked
across New Castle County
Severity Distribution
across New Castle County
Highest-Severity Sites
Know Before You Grow
- •Underground tanks leak petroleum as they age — near a former filling station, test the soil.
- •Near a brownfield, raised beds of imported soil give your food clean ground.
- •On a private well, test for nitrates: above 10 mg/L the water needs treatment before irrigating.
Check your specific parcel in New Castle 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 New Castle County average
Your land is one point inside New Castle County
Everything above resolves to New Castle County as a whole — one PHZM band and one county frost record, read across 273K 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 New Castle County Average
New Castle County Average
- ●USDA Zones 7b, averaged across New Castle County
- ●One soil character for all of New Castle County
- ●Frost dates read at New Castle County's scale: Mar 23 to Nov 19
YOUR Parcel
- ✓Your exact zone, not New Castle County's 7b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in New Castle County
Pull a site-specific report for your exact address in New Castle County, Delaware — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that New Castle County averages can't show:
We read public map data around New Castle County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the New Castle County average
How we know this about New Castle 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 New Castle County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about New Castle County
When does frost risk typically end in New Castle County?
The last hard freeze (28°F) in New Castle County typically lands around Mar 23, 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 Apr 13.
How long is the growing season in New Castle County?
Measured between 28°F hard freezes, New Castle County sees about 241 frost-free days — roughly Mar 23 through Nov 19, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Apr 13 to Nov 5, about 206 days.
Is the soil safe to grow vegetables in New Castle County?
The federal record around New Castle County runs heavier than most — 3,080 documented sites, mostly Underground Storage Tanks entries (1,461), the nearest Underground Storage Tanks record about 0.3 miles out — so test the soil before planting food in the ground, and raised beds with clean imported soil grow well in the meantime. Even here, proximity to a documented site is information, not a diagnosis of any one yard; the contamination map shows exactly what's recorded and where.
Everything above is measured at New Castle County's scale — its 7b band and its 241-day season. Your yard writes its own version of New Castle 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 Delaware's frost window, season length, and soil profile against the plant's real requirements.
What this page reads at New Castle County’s own scale
9 of the readings below were taken at New Castle County's own scale — its own ~241-day span between 28°F freezes, the 3 most extensive soil series mapped here and 3,080 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- New Castle County's own USDA hardiness band, zones 7bUSDA PHZM 2023
- New Castle County's own 28°F hard-freeze dates and its ~241-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in New Castle CountyUSDA NRCS SSURGO
- 3,080 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Underground Storage Tanks record about 0.3 miles outFederal environmental registers
- New Castle County's boundary and the 272,856 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 7b and a ~241-day seasonGrowable Ground crop-matching engine
- The 2 ecoregions New Castle County spans, Middle Atlantic Coastal Plain the largestUS EPA Level III Ecoregions
- Open occurrence records documented in New Castle County for 2 tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto New Castle County farmland, and roughly how muchUSGS NAWQA EPest county estimates
Inherited from a wider read
- The growing challenges every Delaware grower plans around — written at state scale, so they stay on the state guidefrom Delaware
What this page can’t tell you
- How the season shifts across New Castle County — the ~241 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 New Castle County's 272,856 acreswhy one lot differs from the next →
- Which of those 3,080 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 New Castle Countyread your own land →