Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated

Planting zone for 20643 — Ironsides, MD

ZIP code 20643 (Ironsides, Charles County) is in USDA zone 7b: the coldest winter night averages 5 to 10 °F. The median last spring frost is March 28 and the first fall frost November 8.

Where ZIP 20643 is

tap the map for the zone at any spot · scroll or pinch to zoom

Not the official USDA Plant Hardiness Zone Map. Zones come from the 2023 USDA hardiness-zone data by the PRISM Group, Oregon State University; we re-mapped and recolored them. The official map is at planthardiness.ars.usda.gov.

Zone7b5 to 10 °F
Coldest night−15 to −12.2 °C
Last frostMar 28
First frostNov 8
2012 zone7a

Was 7a on the 2012 map — half a zone warmer now. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 7b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Ironsides, MD…

Forecast data: National Weather Service (api.weather.gov), public domain. This is not a warning service — for official frost and freeze warnings see weather.gov.

Frost dates in Ironsides, MD

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMarch 28median — 50% chance of a later frost
Safe for tender plantsApril 8only 10% chance of frost after
First fall frostNovember 8median — 10% chance by Oct 28
Growing season226 daysfrost-free, median

A hard freeze (28 °F) usually ends around March 17 and returns around November 22.

From the NOAA station Quantico Mcas, VA — 8 miles away, elevation 10 ft. NOAA NCEI U.S. Climate Normals 1991–2020, 32 °F threshold. Low spots and valleys can freeze later in spring than the station.

When to plant vegetables in 20643

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Feb 14 – Feb 28
SpinachSow outdoors · Feb 14 – Mar 7
Broccoli, cabbageStart indoors · Jan 17 – Jan 31
Broccoli, cabbageTransplant · Mar 7 – Mar 21
Onion setsPlant outdoors · Feb 28 – Mar 14
PotatoesPlant outdoors · Mar 7 – Mar 21
LettuceSow outdoors · Feb 28 – Mar 14
Carrots, beetsSow outdoors · Mar 7 – Mar 21
TomatoesStart indoors · Jan 31 – Feb 14
TomatoesTransplant · Apr 4 – Apr 18
Peppers, eggplantStart indoors · Jan 17 – Jan 31
Peppers, eggplantTransplant · Apr 11 – Apr 25
BeansSow outdoors · Apr 4 – Apr 18
Sweet cornSow outdoors · Apr 4 – Apr 18
Cucumbers, squashSow outdoors · Apr 4 – Apr 18
Fall lettuce, spinachSow outdoors · Sep 13 – Sep 27
GarlicPlant cloves · Oct 25 – Nov 29
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Mar 28) and first fall frost (Nov 8) with the rules of thumb U.S. extension services publish. Cool-season crops take a light frost; warm-season crops do best once the soil is above about 60 °F.

When spring arrived in 2026

In 2026, spring leaf-out near 20643 came on Mar 10 — about the same time as the 1991–2020 average (Mar 8).

JanFebMarAprMayJun

The Spring Index marks the day when accumulated warmth is enough for lilac and honeysuckle to leaf out — a widely used signal that the growing season has started. Source: USA National Phenology Network, www.usanpn.org — Spring Indices, first leaf, 2026 (data as of 2026-09-08) and 30-year average 1991–2020 (CC BY 4.0).

Soil in Ironsides, MD

The soil mapped at the center of ZIP 20643 is Grosstown — gravelly silt loam, well drained.

TextureGravelly silt loama good balance for most vegetables
pH4.1strongly acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter4%moderate
Hydrologic groupAwater soaks in fast
Farmland classNot prime farmlandUSDA classification

Map unit: Grosstown-Marr-Hoghole complex, 15 to 40 percent slopes.

Soil Survey Staff, Natural Resources Conservation Service, USDA. Soil Survey Geographic (SSURGO) Database, via Soil Data Access, accessed 2026-10-29. The soil at the center point of ZIP 20643; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Ironsides, MD

Summer high88 °Faverage high, July
Winter low28 °Faverage low, January
Hot days30days a year at 90 °F or more
Freezing nights76nights a year at 32 °F or less
Growing degree days4,379base 50 °F — the season’s usable heat
Longest day14 h 51 mindaylight on June 21
Shortest day9 h 28 mindaylight on December 21
Onions to growIntermediateday-neutral types bulb best; long-day varieties may not bulb fully
Precipitation46.9 inper year, rain and melted snow

Average high and low, by month

20°30°40°50°60°70°80°90°100°32 °FJanuary: average high 45 °F, low 28 °F 45°28° JanFebruary: average high 48 °F, low 30 °F 48°30° FebMarch: average high 56 °F, low 37 °F 56°37° MarApril: average high 68 °F, low 47 °F 68°47° AprMay: average high 76 °F, low 57 °F 76°57° MayJune: average high 84 °F, low 66 °F 84°66° JunJuly: average high 88 °F, low 71 °F 88°71° JulAugust: average high 86 °F, low 69 °F 86°69° AugSeptember: average high 80 °F, low 62 °F 80°62° SepOctober: average high 69 °F, low 50 °F 69°50° OctNovember: average high 58 °F, low 39 °F 58°39° NovDecember: average high 49 °F, low 32 °F 49°32° Dec

Precipitation by month inches

0″1″2″3″4″5″January: 3.15 in precipitation 3.1 JanFebruary: 2.84 in precipitation 2.8 FebMarch: 3.85 in precipitation 3.9 MarApril: 3.87 in precipitation 3.9 AprMay: 4.33 in precipitation 4.3 MayJune: 4.23 in precipitation 4.2 JunJuly: 4.57 in precipitation 4.6 JulAugust: 4.53 in precipitation 4.5 AugSeptember: 4.35 in precipitation 4.3 SepOctober: 4.09 in precipitation 4.1 OctNovember: 3.43 in precipitation 3.4 NovDecember: 3.67 in precipitation 3.7 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Quantico Mcas, VA (8 mi away); precipitation: Port Tobacco Village 1.0 S, MD (7 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 7b.

206407b
Indian Head, MD · 3 mi
206937b
Welcome, MD · 5 mi
206587b
Marbury, MD · 5 mi
206627b
Nanjemoy, MD · 6 mi
206777b
Port Tobacco, MD · 6 mi
221357b
Quantico, VA · 8 mi
206467b
La Plata, MD · 8 mi
220267b
Dumfries, VA · 9 mi

Maryland planting zones →

Questions about 20643

What planting zone is ZIP code 20643?

ZIP code 20643 (Ironsides, MD) is in USDA hardiness zone 7b on the 2023 map: the coldest night of an average winter reaches 5 to 10 °F (−15 to −12.2 °C).

When is the last frost in Ironsides, MD?

The median last spring frost (32 °F) near 20643 is March 28; after April 8 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Quantico Mcas station.

When is the first frost in Ironsides, MD?

The median first fall frost near 20643 is November 8, giving a median frost-free growing season of 226 days.

When should I plant tomatoes in 20643?

Start tomato seeds indoors around Jan 31 – Feb 14 and set transplants outside around Apr 4 – Apr 18, one to three weeks after the median last frost.

How much rain and snow does 20643 get?

About 46.9 inches of precipitation a year (NOAA 1991–2020 normals, Port Tobacco Village 1.0 S station).

How hot do summers get in Ironsides, MD?

The average high peaks at 88 °F in July, with about 30 days a year at 90 °F or more.

What kind of soil does 20643 have?

The USDA soil survey maps Grosstown at the center of ZIP 20643: gravelly silt loam, well drained, pH about 4.1 (strongly acidic).

Did spring come early in Ironsides, MD in 2026?

Spring leaf-out near 20643 came on Mar 10 in 2026, about the same as the 1991–2020 average (Mar 8), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Ironsides, MD?

Intermediate onions: the longest day near 20643 is 14 h 51 min, so day-neutral types bulb best; long-day varieties may not bulb fully.

Did the zone for 20643 change?

Yes. The 2012 USDA map put 20643 in zone 7a; the 2023 map puts it in zone 7b. The newer map uses 1991–2020 data and more weather stations.