Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated Oct 29, 2026

Planting zone for 21641 — Hillsboro, MD

ZIP code 21641 (Hillsboro, Caroline County) is in USDA zone 7b: the coldest winter night averages 5 to 10 °F. The median last spring frost is April 1 and the first fall frost November 7.

Where ZIP 21641 is

Outlined: the ZIP code area · 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 frostApr 1

First frostNov 7

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 Hillsboro, 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 Hillsboro, MD

JanFebMarAprMayJunJulAugSepOctNovDec

Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free

Last spring frostApril 1median — 50% chance of a later frost

Safe for tender plantsApril 15only 10% chance of frost after

First fall frostNovember 7median — 10% chance by Oct 24

Growing season220 daysfrost-free, median

A hard freeze (28 °F) usually ends around March 20 and returns around November 20.

From the NOAA station Royal Oak 2 Ssw, MD — 19 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 21641

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Feb 18 – Mar 4

SpinachSow outdoors · Feb 18 – Mar 11

Broccoli, cabbageStart indoors · Jan 21 – Feb 4

Broccoli, cabbageTransplant · Mar 11 – Mar 25

Onion setsPlant outdoors · Mar 4 – Mar 18

PotatoesPlant outdoors · Mar 11 – Mar 25

LettuceSow outdoors · Mar 4 – Mar 18

Carrots, beetsSow outdoors · Mar 11 – Mar 25

TomatoesStart indoors · Feb 4 – Feb 18

TomatoesTransplant · Apr 8 – Apr 22

Peppers, eggplantStart indoors · Jan 21 – Feb 4

Peppers, eggplantTransplant · Apr 15 – Apr 29

BeansSow outdoors · Apr 8 – Apr 22

Sweet cornSow outdoors · Apr 8 – Apr 22

Cucumbers, squashSow outdoors · Apr 8 – Apr 22

Fall lettuce, spinachSow outdoors · Sep 12 – Sep 26

GarlicPlant cloves · Oct 24 – Nov 28

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 1) and first fall frost (Nov 7) 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 21641 came on Mar 12 — about the same time as the 1991–2020 average (Mar 12).

average
Mar 122026
Mar 12

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).

Native plants for zone 7b in Maryland

618 plants native to the lower 48 states, recorded in Maryland, and rated by the USDA to survive 5 °F or colder — the bottom of zone 7b. Each links to its USDA PLANTS profile.

Source: USDA, NRCS. 2026. The PLANTS Database (plants.usda.gov), National Plant Data Team — state distribution, native status and the “Temperature, Minimum” characteristic. Check light, moisture and soil needs before buying; local nurseries and your state native plant society can confirm what thrives in Hillsboro, MD.

Soil in Hillsboro, MD

The soil mapped at the center of ZIP 21641 is Ingleside — sandy loam, well drained.

TextureSandy loamdrains and warms fast; dries out and needs more feeding

pH6.2slightly acidic; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter1.2%low — add compost

Hydrologic groupAwater soaks in fast

Farmland classprime farmlandUSDA classification

Map unit: Ingleside sandy loam, 2 to 5 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 21641; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Hillsboro, MD

Summer high88 °Faverage high, July

Winter low29 °Faverage low, January

Hot days32days a year at 90 °F or more

Freezing nights69nights a year at 32 °F or less

Growing degree days4,342base 50 °F — the season’s usable heat

Longest day14 h 54 mindaylight on June 21

Shortest day9 h 26 mindaylight on December 21

Onions to growIntermediateday-neutral types bulb best; long-day varieties may not bulb fully

Precipitation47.8 inper year, rain and melted snow

Average high and low, by month

Precipitation by month inches

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Royal Oak 2 Ssw, MD (19 mi away); precipitation: Denton 5.8 Wsw, MD (4 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 7b.

216577b

Queen Anne, MD · 3 mi

Greensboro, MD · 9 mi

216367b

Goldsboro, MD · 10 mi

216177b

Centreville, MD · 11 mi

Maryland planting zones →

Questions about 21641

What planting zone is ZIP code 21641?

ZIP code 21641 (Hillsboro, 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 Hillsboro, MD?

The median last spring frost (32 °F) near 21641 is April 1; after April 15 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Royal Oak 2 Ssw station.

When is the first frost in Hillsboro, MD?

The median first fall frost near 21641 is November 7, giving a median frost-free growing season of 220 days.

When should I plant tomatoes in 21641?

Start tomato seeds indoors around Feb 4 – Feb 18 and set transplants outside around Apr 8 – Apr 22, one to three weeks after the median last frost.

How much rain and snow does 21641 get?

About 47.8 inches of precipitation a year (NOAA 1991–2020 normals, Denton 5.8 Wsw station).

How hot do summers get in Hillsboro, MD?

The average high peaks at 88 °F in July, with about 32 days a year at 90 °F or more.

What kind of soil does 21641 have?

The USDA soil survey maps Ingleside at the center of ZIP 21641: sandy loam, well drained, pH about 6.2 (slightly acidic).

Did spring come early in Hillsboro, MD in 2026?

Spring leaf-out near 21641 came on Mar 12 in 2026, about the same as the 1991–2020 average (Mar 12), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Hillsboro, MD?

Intermediate onions: the longest day near 21641 is 14 h 54 min, so day-neutral types bulb best; long-day varieties may not bulb fully.

Did the zone for 21641 change?

Yes. The 2012 USDA map put 21641 in zone 7a; the 2023 map puts it in zone 7b. The newer map uses 1991–2020 data and more weather stations.