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

Planting zone for 21918 — Conowingo, MD

ZIP code 21918 (Conowingo, Cecil County) is in USDA zone 7a: the coldest winter night averages 0 to 5 °F. The median last spring frost is April 3 and the first fall frost November 6.

Where ZIP 21918 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.

Zone7a0 to 5 °F

Coldest night−17.8 to −15 °C

Last frostApr 3

First frostNov 6

2012 zone7a

Same zone as on the 2012 map. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 7a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Conowingo, 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 Conowingo, MD

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostApril 3median — 50% chance of a later frost

Safe for tender plantsApril 18only 10% chance of frost after

First fall frostNovember 6median — 10% chance by Oct 26

Growing season217 daysfrost-free, median

A hard freeze (28 °F) usually ends around March 24 and returns around November 17.

From the NOAA station Conowingo Dam, MD — 2 miles away, elevation 39 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 21918

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Feb 20 – Mar 6

SpinachSow outdoors · Feb 20 – Mar 13

Broccoli, cabbageStart indoors · Jan 23 – Feb 6

Broccoli, cabbageTransplant · Mar 13 – Mar 27

Onion setsPlant outdoors · Mar 6 – Mar 20

PotatoesPlant outdoors · Mar 13 – Mar 27

LettuceSow outdoors · Mar 6 – Mar 20

Carrots, beetsSow outdoors · Mar 13 – Mar 27

TomatoesStart indoors · Feb 6 – Feb 20

TomatoesTransplant · Apr 10 – Apr 24

Peppers, eggplantStart indoors · Jan 23 – Feb 6

Peppers, eggplantTransplant · Apr 17 – May 1

BeansSow outdoors · Apr 10 – Apr 24

Sweet cornSow outdoors · Apr 10 – Apr 24

Cucumbers, squashSow outdoors · Apr 10 – Apr 24

Fall lettuce, spinachSow outdoors · Sep 11 – Sep 25

GarlicPlant cloves · Oct 23 – Nov 27

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 3) and first fall frost (Nov 6) 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 21918 came on Mar 19 — 4 days earlier than the 1991–2020 average (Mar 23).

average
Mar 232026
Mar 19

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 7a in Maryland

612 plants native to the lower 48 states, recorded in Maryland, and rated by the USDA to survive 0 °F or colder — the bottom of zone 7a. 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 Conowingo, MD.

Soil in Conowingo, MD

The soil mapped at the center of ZIP 21918 is Legore — silt loam, well drained.

TextureSilt loama good balance for most vegetables

pH5.6moderately acidic; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter2%moderate

Hydrologic groupBwater soaks in moderately

Farmland classNot prime farmlandUSDA classification

Map unit: Legore silt loam, 15 to 25 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 21918; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Conowingo, MD

Summer high88 °Faverage high, July

Winter low25 °Faverage low, January

Hot days37days a year at 90 °F or more

Freezing nights106nights a year at 32 °F or less

Growing degree days3,882base 50 °F — the season’s usable heat

Longest day14 h 59 mindaylight on June 21

Shortest day9 h 21 mindaylight on December 21

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

Precipitation48.3 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: Conowingo Dam, MD (2 mi away); precipitation: Conowingo Dam, MD (2 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

1 of the 8 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

210347a

Darlington, MD · 4 mi

219177a

Colora, MD · 4 mi

175637a

Peach Bottom, PA · 6 mi

211607a

Whiteford, MD · 7 mi

219047a

Port Deposit, MD · 7 mi

193627a

Nottingham, PA · 8 mi

219117a

Rising Sun, MD · 8 mi

210787b

Havre De Grace, MD · 8 mi

Maryland planting zones →

Questions about 21918

What planting zone is ZIP code 21918?

ZIP code 21918 (Conowingo, MD) is in USDA hardiness zone 7a on the 2023 map: the coldest night of an average winter reaches 0 to 5 °F (−17.8 to −15 °C).

When is the last frost in Conowingo, MD?

The median last spring frost (32 °F) near 21918 is April 3; after April 18 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Conowingo Dam station.

When is the first frost in Conowingo, MD?

The median first fall frost near 21918 is November 6, giving a median frost-free growing season of 217 days.

When should I plant tomatoes in 21918?

Start tomato seeds indoors around Feb 6 – Feb 20 and set transplants outside around Apr 10 – Apr 24, one to three weeks after the median last frost.

How much rain and snow does 21918 get?

About 48.3 inches of precipitation a year (NOAA 1991–2020 normals, Conowingo Dam station).

How hot do summers get in Conowingo, MD?

The average high peaks at 88 °F in July, with about 37 days a year at 90 °F or more.

What kind of soil does 21918 have?

The USDA soil survey maps Legore at the center of ZIP 21918: silt loam, well drained, pH about 5.6 (moderately acidic).

Did spring come early in Conowingo, MD in 2026?

Spring leaf-out near 21918 came on Mar 19 in 2026, 4 days earlier than the 1991–2020 average (Mar 23), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Conowingo, MD?

Intermediate onions: the longest day near 21918 is 14 h 59 min, so day-neutral types bulb best; long-day varieties may not bulb fully.