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

Planting zone for 18099 — Emmaus, PA

ZIP code 18099 (Emmaus, Lehigh County) is in USDA zone 7a: the coldest winter night averages 0 to 5 °F. The median last spring frost is April 20 and the first fall frost October 24.

Where ZIP 18099 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.

Zone7a0 to 5 °F
Coldest night−17.8 to −15 °C
Last frostApr 20
First frostOct 24
2012 zone6b

Was 6b 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 7a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Emmaus, 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 Emmaus, PA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 20median — 50% chance of a later frost
Safe for tender plantsMay 6only 10% chance of frost after
First fall frostOctober 24median — 10% chance by Oct 8
Growing season184 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 5 and returns around November 4.

From the NOAA station Allentown Intl Airport, PA — 8 miles away, elevation 390 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 18099

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 9 – Mar 23
SpinachSow outdoors · Mar 9 – Mar 30
Broccoli, cabbageStart indoors · Feb 9 – Feb 23
Broccoli, cabbageTransplant · Mar 30 – Apr 13
Onion setsPlant outdoors · Mar 23 – Apr 6
PotatoesPlant outdoors · Mar 30 – Apr 13
LettuceSow outdoors · Mar 23 – Apr 6
Carrots, beetsSow outdoors · Mar 30 – Apr 13
TomatoesStart indoors · Feb 23 – Mar 9
TomatoesTransplant · Apr 27 – May 11
Peppers, eggplantStart indoors · Feb 9 – Feb 23
Peppers, eggplantTransplant · May 4 – May 18
BeansSow outdoors · Apr 27 – May 11
Sweet cornSow outdoors · Apr 27 – May 11
Cucumbers, squashSow outdoors · Apr 27 – May 11
Fall lettuce, spinachSow outdoors · Aug 29 – Sep 12
GarlicPlant cloves · Oct 10 – Nov 14
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 20) and first fall frost (Oct 24) 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 18099 came on Mar 25 — 6 days earlier than the 1991–2020 average (Mar 31).

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 Pennsylvania

620 plants native to the lower 48 states, recorded in Pennsylvania, and rated by the USDA to survive 0 °F or colder — the bottom of zone 7a. Each links to its USDA PLANTS profile.

Trees 78

American basswood100 ft · blooms late spring · low shade tolerance · to −46 °FAmerican beech80 ft · blooms mid spring · low shade tolerance · to −44 °FAmerican chestnut115 ft · blooms early summer · high shade tolerance · to −33 °FAmerican elm120 ft · blooms early spring · medium shade tolerance · to −46 °FAmerican sycamore100 ft · blooms spring · medium shade tolerance · to −34 °Farborvitae50 ft · blooms mid spring · medium shade tolerance · to −33 °F

Shrubs 123

alderleaf buckthorn3 ft · blooms late spring · low shade tolerance · to −33 °FAllegheny serviceberry35 ft · blooms early spring · low shade tolerance · to −38 °Falternateleaf dogwood25 ft · blooms mid spring · low shade tolerance · to −47 °FAmerican black currant3 ft · blooms early spring · to −46 °FAmerican hazelnut10 ft · blooms spring · medium shade tolerance · to −33 °FAmerican holly40 ft · blooms mid spring · low shade tolerance · to −20 °F

Wildflowers & perennials 212

alkali buttercup1 ft · blooms late spring · low shade tolerance · to −38 °FAmerican bur-reed3 ft · blooms indeterminate · medium shade tolerance · to −33 °FAmerican eelgrass1 ft · blooms mid summer · high shade tolerance · to −33 °FAmerican licorice4 ft · blooms late spring · medium shade tolerance · to −38 °FAmerican lotus3 ft · blooms mid summer · high shade tolerance · to −36 °FAmerican pokeweed7 ft · blooms mid summer · low shade tolerance · to −33 °F

Grasses 181

American beachgrass2.5 ft · blooms spring · high shade tolerance · to −28 °Farctic brome3 ft · blooms early summer · low shade tolerance · to −33 °FAtlantic mannagrass3 ft · blooms summer · low shade tolerance · to −8 °Fautumn bluegrass1.5 ft · blooms late spring · medium shade tolerance · to −8 °Fawlfruit sedge4 ft · blooms mid spring · low shade tolerance · to −38 °FBailey's sedge2.1 ft · blooms late spring · low shade tolerance · to −33 °F

Vines 11

American bittersweet15 ft · blooms spring · low shade tolerance · to −38 °FAmerican wisteria50 ft · blooms spring · low shade tolerance · to −3 °Fdevil's darning needles15 ft · blooms mid summer · medium shade tolerance · to −38 °Ffrost grape83 ft · blooms late spring · medium shade tolerance · to −23 °Fgraybark grape50 ft · blooms late spring · medium shade tolerance · to −8 °Friverbank grape45 ft · blooms late spring · medium shade tolerance · to −33 °F

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 Emmaus, PA.

Soil in Emmaus, PA

The soil mapped at the center of ZIP 18099 is Duffield — silt loam, well drained. Much of the area is built over (urban land); this is the natural soil underneath.

TextureSilt loama good balance for most vegetables
pH6.7neutral; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter3%moderate
Hydrologic groupBwater soaks in moderately
Farmland classNot prime farmlandUSDA classification

Map unit: Urban land-Duffield complex, 0 to 8 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 18099; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Emmaus, PA

Summer high86 °Faverage high, July
Winter low22 °Faverage low, January
Hot days18days a year at 90 °F or more
Freezing nights118nights a year at 32 °F or less
Growing degree days3,405base 50 °F — the season’s usable heat
Longest day15 h 04 mindaylight on June 21
Shortest day9 h 16 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation47.4 inper year, rain and melted snow
Snowfall33 inper year; 31 days with snow on the ground

Average high and low, by month

10°20°30°40°50°60°70°80°90°100°32 °FJanuary: average high 38 °F, low 22 °F 38°22° JanFebruary: average high 42 °F, low 23 °F 42°23° FebMarch: average high 51 °F, low 31 °F 51°31° MarApril: average high 63 °F, low 40 °F 63°40° AprMay: average high 74 °F, low 51 °F 74°51° MayJune: average high 82 °F, low 60 °F 82°60° JunJuly: average high 86 °F, low 65 °F 86°65° JulAugust: average high 84 °F, low 63 °F 84°63° AugSeptember: average high 77 °F, low 55 °F 77°55° SepOctober: average high 66 °F, low 44 °F 66°44° OctNovember: average high 54 °F, low 34 °F 54°34° NovDecember: average high 43 °F, low 27 °F 43°27° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″4″5″6″January: 3.30 in precipitation, 9.8 in snowfall 3.3❄10 JanFebruary: 2.77 in precipitation, 10.8 in snowfall 2.8❄11 FebMarch: 3.63 in precipitation, 6.3 in snowfall 3.6❄6 MarApril: 3.67 in precipitation, 0.5 in snowfall 3.7❄1 AprMay: 3.65 in precipitation 3.6 MayJune: 4.40 in precipitation 4.4 JunJuly: 5.30 in precipitation 5.3 JulAugust: 4.56 in precipitation 4.6 AugSeptember: 4.84 in precipitation 4.8 SepOctober: 4.14 in precipitation, 0.2 in snowfall 4.1 OctNovember: 3.24 in precipitation, 0.9 in snowfall 3.2❄1 NovDecember: 3.86 in precipitation, 4.6 in snowfall 3.9❄5 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Allentown Intl Airport, PA (8 mi away); precipitation: Allentown Intl Airport, PA (8 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 7a.

180987a
Emmaus, PA · <1 mi
180497a
Emmaus, PA · 1 mi
181037a
Allentown, PA · 2 mi
180607a
Limeport, PA · 3 mi
180467a
East Texas, PA · 3 mi
180687a
Old Zionsville, PA · 4 mi
181067a
Allentown, PA · 4 mi
180347a
Center Valley, PA · 4 mi

All 3 ZIP codes in Emmaus → · Pennsylvania planting zones →

Questions about 18099

What planting zone is ZIP code 18099?

ZIP code 18099 (Emmaus, PA) 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 Emmaus, PA?

The median last spring frost (32 °F) near 18099 is April 20; after May 6 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Allentown Intl Airport station.

When is the first frost in Emmaus, PA?

The median first fall frost near 18099 is October 24, giving a median frost-free growing season of 184 days.

When should I plant tomatoes in 18099?

Start tomato seeds indoors around Feb 23 – Mar 9 and set transplants outside around Apr 27 – May 11, one to three weeks after the median last frost.

How much rain and snow does 18099 get?

About 47.4 inches of precipitation a year and 33 inches of snowfall (NOAA 1991–2020 normals, Allentown Intl Airport station).

How hot do summers get in Emmaus, PA?

The average high peaks at 86 °F in July, with about 18 days a year at 90 °F or more.

What kind of soil does 18099 have?

The USDA soil survey maps Duffield at the center of ZIP 18099: silt loam, well drained, pH about 6.7 (neutral).

Did spring come early in Emmaus, PA in 2026?

Spring leaf-out near 18099 came on Mar 25 in 2026, 6 days earlier than the 1991–2020 average (Mar 31), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Emmaus, PA?

Long-day onions: the longest day near 18099 is 15 h 04 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 18099 change?

Yes. The 2012 USDA map put 18099 in zone 6b; the 2023 map puts it in zone 7a. The newer map uses 1991–2020 data and more weather stations.