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

Planting zone for 46373 — Saint John, IN

ZIP code 46373 (Saint John, Lake County) is in USDA zone 6a: the coldest winter night averages −10 to −5 °F. The median last spring frost is April 23 and the first fall frost October 20.

Where ZIP 46373 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 frostApr 23
First frostOct 20
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 Saint John, IN…

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 Saint John, IN

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 23median — 50% chance of a later frost
Safe for tender plantsMay 11only 10% chance of frost after
First fall frostOctober 20median — 10% chance by Oct 6
Growing season179 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 12 and returns around October 30.

From the NOAA station Park Forest, IL — 12 miles away, elevation 709 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 46373

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 12 – Mar 26
SpinachSow outdoors · Mar 12 – Apr 2
Broccoli, cabbageStart indoors · Feb 12 – Feb 26
Broccoli, cabbageTransplant · Apr 2 – Apr 16
Onion setsPlant outdoors · Mar 26 – Apr 9
PotatoesPlant outdoors · Apr 2 – Apr 16
LettuceSow outdoors · Mar 26 – Apr 9
Carrots, beetsSow outdoors · Apr 2 – Apr 16
TomatoesStart indoors · Feb 26 – Mar 12
TomatoesTransplant · Apr 30 – May 14
Peppers, eggplantStart indoors · Feb 12 – Feb 26
Peppers, eggplantTransplant · May 7 – May 21
BeansSow outdoors · Apr 30 – May 14
Sweet cornSow outdoors · Apr 30 – May 14
Cucumbers, squashSow outdoors · Apr 30 – May 14
Fall lettuce, spinachSow outdoors · Aug 25 – Sep 8
GarlicPlant cloves · Oct 6 – Nov 10
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 23) and first fall frost (Oct 20) 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 46373 came on Mar 21 — 15 days earlier than the 1991–2020 average (Apr 5).

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 6a in Indiana

558 plants native to the lower 48 states, recorded in Indiana, and rated by the USDA to survive −10 °F or colder — the bottom of zone 6a. Each links to its USDA PLANTS profile.

Trees 71

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 105

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 200

American 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 °FAmerican speedwell0.8 ft · blooms mid summer · low shade tolerance · to −38 °F

Grasses 161

American beachgrass2.5 ft · blooms spring · high shade tolerance · to −28 °Farctic brome3 ft · blooms early summer · low shade tolerance · to −33 °Fawlfruit sedge4 ft · blooms mid spring · low shade tolerance · to −38 °Fbeaked spikerush3 ft · blooms late spring · high shade tolerance · to −28 °FBebb's sedge3 ft · blooms late spring · low shade tolerance · to −38 °FBicknell's sedge3 ft · blooms late spring · low shade tolerance · to −38 °F

Vines 9

American bittersweet15 ft · blooms spring · low shade tolerance · to −38 °Fcatbird grape30 ft · blooms late spring · medium shade tolerance · to −13 °Fdevil's darning needles15 ft · blooms mid summer · medium shade tolerance · to −38 °Ffrost grape83 ft · blooms late spring · medium shade tolerance · to −23 °Friverbank grape45 ft · blooms late spring · medium shade tolerance · to −33 °Fsummer grape30 ft · blooms late spring · low shade tolerance · to −23 °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 Saint John, IN.

Soil in Saint John, IN

The soil mapped at the center of ZIP 46373 is Pewamo — silty clay loam, poorly drained.

TextureSilty clay loamholds water and nutrients; slow to drain and warm up
pH6.7neutral; most vegetables like 6.0–7.0
DrainagePoorly drainedconsider raised beds
Organic matter5%high
Hydrologic groupC/Dslow when drained; wet otherwise
Farmland classPrime farmland if drainedUSDA classification

Map unit: Pewamo silty clay loam.

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 46373; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Saint John, IN

Summer high84 °Faverage high, July
Winter low15 °Faverage low, January
Hot days16days a year at 90 °F or more
Freezing nights126nights a year at 32 °F or less
Growing degree days3,114base 50 °F — the season’s usable heat
Longest day15 h 11 mindaylight on June 21
Shortest day9 h 10 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation39.5 inper year, rain and melted snow

Average high and low, by month

0°10°20°30°40°50°60°70°80°90°32 °FJanuary: average high 31 °F, low 15 °F 31°15° JanFebruary: average high 35 °F, low 18 °F 35°18° FebMarch: average high 46 °F, low 28 °F 46°28° MarApril: average high 59 °F, low 38 °F 59°38° AprMay: average high 71 °F, low 49 °F 71°49° MayJune: average high 80 °F, low 59 °F 80°59° JunJuly: average high 84 °F, low 64 °F 84°64° JulAugust: average high 82 °F, low 62 °F 82°62° AugSeptember: average high 76 °F, low 55 °F 76°55° SepOctober: average high 63 °F, low 42 °F 63°42° OctNovember: average high 48 °F, low 31 °F 48°31° NovDecember: average high 36 °F, low 22 °F 36°22° Dec

Precipitation by month inches

0″1″2″3″4″5″January: 2.32 in precipitation 2.3 JanFebruary: 2.07 in precipitation 2.1 FebMarch: 2.28 in precipitation 2.3 MarApril: 3.68 in precipitation 3.7 AprMay: 4.10 in precipitation 4.1 MayJune: 4.68 in precipitation 4.7 JunJuly: 4.25 in precipitation 4.3 JulAugust: 4.27 in precipitation 4.3 AugSeptember: 3.36 in precipitation 3.4 SepOctober: 3.63 in precipitation 3.6 OctNovember: 2.74 in precipitation 2.7 NovDecember: 2.13 in precipitation 2.1 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Park Forest, IL (12 mi away); precipitation: St. John 0.2 Wsw, IN (within 1 mile). 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.

463116a
Dyer, IN · 3 mi
463756a
Schererville, IN · 4 mi
463035b
Cedar Lake, IN · 5 mi
463256a
Hammond, IN · 5 mi
464116a
Merrillville, IN · 5 mi
463085b
Crown Point, IN · 6 mi
463196a
Griffith, IN · 6 mi
604176a
Crete, IL · 6 mi

Indiana planting zones →

Questions about 46373

What planting zone is ZIP code 46373?

ZIP code 46373 (Saint John, IN) 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 Saint John, IN?

The median last spring frost (32 °F) near 46373 is April 23; after May 11 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Park Forest station.

When is the first frost in Saint John, IN?

The median first fall frost near 46373 is October 20, giving a median frost-free growing season of 179 days.

When should I plant tomatoes in 46373?

Start tomato seeds indoors around Feb 26 – Mar 12 and set transplants outside around Apr 30 – May 14, one to three weeks after the median last frost.

How much rain and snow does 46373 get?

About 39.5 inches of precipitation a year (NOAA 1991–2020 normals, St. John 0.2 Wsw station).

How hot do summers get in Saint John, IN?

The average high peaks at 84 °F in July, with about 16 days a year at 90 °F or more.

What kind of soil does 46373 have?

The USDA soil survey maps Pewamo at the center of ZIP 46373: silty clay loam, poorly drained, pH about 6.7 (neutral).

Did spring come early in Saint John, IN in 2026?

Spring leaf-out near 46373 came on Mar 21 in 2026, 15 days earlier than the 1991–2020 average (Apr 5), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Saint John, IN?

Long-day onions: the longest day near 46373 is 15 h 11 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 46373 change?

Yes. The 2012 USDA map put 46373 in zone 5b; the 2023 map puts it in zone 6a. The newer map uses 1991–2020 data and more weather stations.