Union Mill, Virginia, sits in USDA hardiness zone 7a — a range where zone-matched perennials and frost-aware annual timing set what succeeds.
Among the crops suited to this profile: cabbage, hazelnut, california poppy, and collard greens. The site-level story — soil, sun, drainage — decides the rest.
Even in Union Mill, 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 Union Mill 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 Union Mill — soil, climate, flood, and parcel records. How we handle your address.
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Union Mill — the short answer
Union Mill, Virginia: USDA zone 7a, about 223 days between hard freezes, across 6K acres of town.
- USDA zone
- 7a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Mar 29
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Nov 7
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~223
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Town area
- 6K acres
- US Census TIGER/Line 2025
Every figure names the dataset it came from. Hard-freeze dates are this town’s own 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 7a is Union Mill's average, not your lot's — a low corner or a tree line moves it. Against Union Mill's 223-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Union Mill
Each reading below is measured for Union Mill itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredUnion Mill runs about 223 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
MeasuredUnion Mill sits in USDA hardiness zone 7a.
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 Union Mill is in
Union Mill sits in the Piedmont — EPA Level III, inside the wider Eastern Temperate Forests. That is read at Union Mill's own centroid rather than borrowed from Fairfax County.
What Grows in Union Mill
Every plant below cleared Union Mill's own zone 7a and its 223-day season. Each card opens that plant's Virginia profile. How we score.
Is it too late to plant in Union Mill?
Usually not — gardeners here simply switch what goes in the ground as the season moves. Cool-season crops can go in from around Mar 1; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Mar 29 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Nov 7 — long-season crops need about 90 days of runway, quick greens only 30. A long window like this one runs successions deep into fall — and even its last weeks take quick greens and garlic.
Documented around Union Mill
Spotted lanternfly documented 2 miles from Union Mill, first recorded 2020. What to watch for.
What's on the federal record near Union Mill
Closest first, within ~10 miles of Union Mill. Listing isn't leaking, and distance isn't exposure.
- TWIN LAKES GOLF COURSEUnderground Storage Tanks · 1.1 mi
- CLIFTON ELEMENTARY SCHOOLToxics Release Inventory · 1.1 mi
- CLIFTON ELEMENTARYUnderground Storage Tanks · 1.1 mi
- Fairfax County Fire Station 16Underground Storage Tanks · 1.4 mi
- CLIFTON SUPERETTEUnderground Storage Tanks · 1.4 mi
- CLIFTON CHURCHUnderground Storage Tanks · 1.4 mi
- MOUSER R S (DVM)Underground Storage Tanks · 1.8 mi
- TWIN LAKES GOLF COURSEToxics Release Inventory · 1.9 mi
- TWIN LAKES GOLF COURSEBrownfields · 1.9 mi
- 51U 145Nitrate · 2.1 mi
- CENTERVILLE HIGH SCHOOLUnderground Storage Tanks · 2.2 mi
- CENTREVILLE HIGH SCHOOLToxics Release Inventory · 2.2 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Union Mill'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 Union Mill.
Total Sites
1,660
within ~10 miles of Union Mill
Risk Level
Elevated
Highest-severity
2 Superfund sites (none NPL-listed)
Sources Checked
within ~10 miles of Union Mill
Severity Distribution
within ~10 miles of Union Mill
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.
- •TRI facilities report what they release. Check the wind — downwind beds catch more of it.
Check your specific parcel in Union Mill
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 Union Mill average
Your land is one point inside Union Mill
Everything above resolves to Union Mill as a whole — one PHZM band and one 28°F frost record, read across 6K 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 town 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 Union Mill Average
Union Mill Average
- ●USDA Zones 7a, averaged across Union Mill
- ●One soil character for all of Union Mill
- ●Frost dates read at Union Mill's scale: Mar 29 to Nov 7
YOUR Parcel
- ✓Your exact zone, not Union Mill's 7a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Union Mill
Pull a site-specific report for your exact address in Union Mill, Virginia — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Union Mill averages can't show:
We read public map data around Union Mill — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Union Mill average
How we know this about Union Mill
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at this town’s own centroid; hard-freeze dates from NOAA 1991–2020 28°F normals at Union Mill’s own record; 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 town grain anywhere on this page — there is no town-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 Union Mill
When does frost risk typically end in Union Mill?
The last hard freeze (28°F) in Union Mill typically lands around Mar 29, 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 19.
When is the first frost in Union Mill?
The first hard freeze (28°F) in Union Mill typically arrives around Nov 7, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Oct 24, so the watching starts about Oct 8 — about 223 days after the spring freeze cleared.
How long is the growing season in Union Mill?
Measured between 28°F hard freezes, Union Mill sees about 223 frost-free days — roughly Mar 29 through Nov 7, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Apr 19 to Oct 24, about 188 days.
Is the soil safe to grow vegetables in Union Mill?
The federal record around Union Mill is a meaningful one — 1,660 documented sites, mostly Underground Storage Tanks entries (838), the nearest Underground Storage Tanks record about 1.1 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 Union Mill?
From about Oct 8 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 Nov 7 (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 Nov 7. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Union Mill's scale — its 7a band and its 223-day season. Your yard writes its own version of Union Mill'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 Union Mill’s own scale
7 of the readings below were taken at Union Mill's own scale — its own ~223-day season between 28°F freezes, the 6,390 acres it covers and 1,660 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Union Mill's own USDA hardiness band, zones 7aUSDA PHZM 2023
- Union Mill's own 28°F hard-freeze dates, about Mar 29 and Nov 7 and the ~223-day span between themNOAA 1991–2020 Climate Normals
- 1,660 documented contamination sites on the federal record near Union Mill, the closest Underground Storage Tanks record about 1.1 miles out from the town centreFederal environmental registers
- Union Mill's boundary and the 6,390 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 7a and a ~223-day seasonGrowable Ground crop-matching engine
- The ecoregion at Union Mill's own centroid, the PiedmontUS EPA Level III Ecoregions
- A documented spotted-lanternfly record within reach of Union Milllydemapr (De Bona & Helmus), 10 km survey lattice
Inherited from a wider read
- Soil character — no town-scale survey exists, so Union Mill's 6,390 acres read through its county's SSURGO summaryfrom Fairfax County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Fairfax County
- The growing challenges every Virginia grower plans around — written at state scale, so they stay on the state guidefrom Virginia
- Butterfly and beetle records, and the farmland pesticide estimate — all published county-widefrom Fairfax County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Union Mill's 6,390 acreswhy one lot differs from the next →
- Which side of Union Mill you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 6,390 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Underground Storage Tanks record about 1.1 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 Union Mill-wide figureread your own land →