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

Planting zone for 18823 — Harford, PA

ZIP code 18823 (Harford, Susquehanna County) is in USDA zone 6a: the coldest winter night averages −10 to −5 °F. The median last spring frost is May 14 and the first fall frost October 2.

Where ZIP 18823 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.

Zone6a−10 to −5 °F

Coldest night−23.3 to −20.6 °C

Last frostMay 14

First frostOct 2

2012 zone5b

Was 5b 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 6a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Harford, PA…

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 Harford, PA

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMay 14median — 50% chance of a later frost

Safe for tender plantsMay 28only 10% chance of frost after

First fall frostOctober 2median — 10% chance by Sep 20

Growing season141 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 2 and returns around October 15.

From the NOAA station Montrose, PA — 10 miles away, elevation 1,421 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 18823

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 2 – Apr 16

SpinachSow outdoors · Apr 2 – Apr 23

Broccoli, cabbageStart indoors · Mar 5 – Mar 19

Broccoli, cabbageTransplant · Apr 23 – May 7

Onion setsPlant outdoors · Apr 16 – Apr 30

PotatoesPlant outdoors · Apr 23 – May 7

LettuceSow outdoors · Apr 16 – Apr 30

Carrots, beetsSow outdoors · Apr 23 – May 7

TomatoesStart indoors · Mar 19 – Apr 2

TomatoesTransplant · May 21 – Jun 4

Peppers, eggplantStart indoors · Mar 5 – Mar 19

Peppers, eggplantTransplant · May 28 – Jun 11

BeansSow outdoors · May 21 – Jun 4

Sweet cornSow outdoors · May 21 – Jun 4

Cucumbers, squashSow outdoors · May 21 – Jun 4

Fall lettuce, spinachSow outdoors · Aug 7 – Aug 21

GarlicPlant cloves · Sep 18 – Oct 23

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 14) and first fall frost (Oct 2) 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 18823 came on Apr 9 — 6 days earlier than the 1991–2020 average (Apr 15).

average
Apr 152026
Apr 9

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 Harford, PA

The soil mapped at the center of ZIP 18823 is Fluvents — gravelly sandy loam, moderately well drained.

TextureGravelly sandy loamdrains and warms fast; dries out and needs more feeding

pH5.5moderately acidic; most vegetables like 6.0–7.0

DrainageModerately well drainednatural drainage class

Organic matter1.25%low — add compost

Hydrologic groupCwater soaks in slowly

Farmland classNot prime farmlandUSDA classification

Map unit: Mixed alluvial land.

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 18823; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Harford, PA

Summer high80 °Faverage high, July

Winter low13 °Faverage low, January

Hot days3days a year at 90 °F or more

Freezing nights168nights a year at 32 °F or less

Growing degree days2,067base 50 °F — the season’s usable heat

Longest day15 h 13 mindaylight on June 21

Shortest day9 h 08 mindaylight on December 21

Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)

Precipitation46.7 inper year, rain and melted snow

Snowfall83 inper year; 89 days with snow on the ground

Average high and low, by month

Precipitation by month inches · ❄ = snowfall

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Montrose, PA (10 mi away); precipitation: Montrose, PA (10 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

South Gibson, PA · 4 mi

188345b

New Milford, PA · 4 mi

Hop Bottom, PA · 7 mi

184416a

Lenoxville, PA · 9 mi

Pennsylvania planting zones →

Questions about 18823

What planting zone is ZIP code 18823?

ZIP code 18823 (Harford, PA) is in USDA hardiness zone 6a on the 2023 map: the coldest night of an average winter reaches −10 to −5 °F (−23.3 to −20.6 °C).

When is the last frost in Harford, PA?

The median last spring frost (32 °F) near 18823 is May 14; after May 28 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Montrose station.

When is the first frost in Harford, PA?

The median first fall frost near 18823 is October 2, giving a median frost-free growing season of 141 days.

When should I plant tomatoes in 18823?

Start tomato seeds indoors around Mar 19 – Apr 2 and set transplants outside around May 21 – Jun 4, one to three weeks after the median last frost.

How much rain and snow does 18823 get?

About 46.7 inches of precipitation a year and 83 inches of snowfall (NOAA 1991–2020 normals, Montrose station).

How hot do summers get in Harford, PA?

The average high peaks at 80 °F in July, with about 3 days a year at 90 °F or more.

What kind of soil does 18823 have?

The USDA soil survey maps Fluvents at the center of ZIP 18823: gravelly sandy loam, moderately well drained, pH about 5.5 (moderately acidic).

Did spring come early in Harford, PA in 2026?

Spring leaf-out near 18823 came on Apr 9 in 2026, 6 days earlier than the 1991–2020 average (Apr 15), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Harford, PA?

Long-day onions: the longest day near 18823 is 15 h 13 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 18823 change?

Yes. The 2012 USDA map put 18823 in zone 5b; the 2023 map puts it in zone 6a. The newer map uses 1991–2020 data and more weather stations.