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

Planting zone for 51357 — Royal, IA

ZIP code 51357 (Royal, Clay County) is in USDA zone 5a: the coldest winter night averages −20 to −15 °F. The median last spring frost is May 2 and the first fall frost October 2.

Where ZIP 51357 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.

Zone5a−20 to −15 °F
Coldest night−28.9 to −26.1 °C
Last frostMay 2
First frostOct 2
2012 zone5a

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 5a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Royal, IA…

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 Royal, IA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 2median — 50% chance of a later frost
Safe for tender plantsMay 15only 10% chance of frost after
First fall frostOctober 2median — 10% chance by Sep 18
Growing season154 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 22 and returns around October 12.

From the NOAA station Spencer Municipal Airport, IA — 8 miles away, elevation 1,339 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 51357

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 21 – Apr 4
SpinachSow outdoors · Mar 21 – Apr 11
Broccoli, cabbageStart indoors · Feb 21 – Mar 7
Broccoli, cabbageTransplant · Apr 11 – Apr 25
Onion setsPlant outdoors · Apr 4 – Apr 18
PotatoesPlant outdoors · Apr 11 – Apr 25
LettuceSow outdoors · Apr 4 – Apr 18
Carrots, beetsSow outdoors · Apr 11 – Apr 25
TomatoesStart indoors · Mar 7 – Mar 21
TomatoesTransplant · May 9 – May 23
Peppers, eggplantStart indoors · Feb 21 – Mar 7
Peppers, eggplantTransplant · May 16 – May 30
BeansSow outdoors · May 9 – May 23
Sweet cornSow outdoors · May 9 – May 23
Cucumbers, squashSow outdoors · May 9 – May 23
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 2) 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 51357 came on Mar 25 — 18 days earlier than the 1991–2020 average (Apr 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 5a in Iowa

461 plants native to the lower 48 states, recorded in Iowa, and rated by the USDA to survive −20 °F or colder — the bottom of zone 5a. Each links to its USDA PLANTS profile.

Trees 46

American basswood100 ft · blooms late spring · low shade tolerance · to −46 °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 °Fbalsam fir60 ft · blooms mid summer · low shade tolerance · to −43 °F

Shrubs 77

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 hornbeam30 ft · blooms mid spring · low shade tolerance · to −34 °F

Wildflowers & perennials 185

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 133

arctic brome3 ft · blooms early summer · low shade tolerance · to −33 °Fawlfruit sedge4 ft · blooms mid spring · low shade tolerance · to −38 °FBebb's sedge3 ft · blooms late spring · low shade tolerance · to −38 °FBicknell's sedge3 ft · blooms late spring · low shade tolerance · to −38 °Fbig bluestem6 ft · blooms summer · high shade tolerance · to −46 °Fblue grama1 ft · blooms early summer · high shade tolerance · to −43 °F

Vines 7

American bittersweet15 ft · blooms spring · low shade tolerance · to −38 °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 °Ftrumpet honeysuckle16 ft · blooms late summer · low 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 Royal, IA.

Soil in Royal, IA

The soil mapped at the center of ZIP 51357 is McCreath — silty clay loam, somewhat poorly drained.

TextureSilty clay loamholds water and nutrients; slow to drain and warm up
pH6.5neutral; most vegetables like 6.0–7.0
DrainageSomewhat poorly drainedconsider raised beds
Organic matter5.5%high
Hydrologic groupC/Dslow when drained; wet otherwise
Farmland classprime farmlandUSDA classification

Map unit: McCreath silty clay loam, 0 to 2 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 51357; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Royal, IA

Summer high85 °Faverage high, July
Winter low8 °Faverage low, January
Hot days19days a year at 90 °F or more
Freezing nights163nights a year at 32 °F or less
Growing degree days2,898base 50 °F — the season’s usable heat
Longest day15 h 22 mindaylight on June 21
Shortest day9 h 00 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation26.8 inper year, rain and melted snow

Average high and low, by month

0°10°20°30°40°50°60°70°80°90°100°32 °FJanuary: average high 26 °F, low 8 °F 26°8° JanFebruary: average high 30 °F, low 13 °F 30°13° FebMarch: average high 44 °F, low 25 °F 44°25° MarApril: average high 59 °F, low 36 °F 59°36° AprMay: average high 71 °F, low 48 °F 71°48° MayJune: average high 81 °F, low 59 °F 81°59° JunJuly: average high 85 °F, low 62 °F 85°62° JulAugust: average high 82 °F, low 59 °F 82°59° AugSeptember: average high 76 °F, low 50 °F 76°50° SepOctober: average high 61 °F, low 37 °F 61°37° OctNovember: average high 45 °F, low 25 °F 45°25° NovDecember: average high 31 °F, low 14 °F 31°14° Dec

Precipitation by month inches

0″1″2″3″4″5″January: 0.25 in precipitation 0.3 JanFebruary: 0.43 in precipitation 0.4 FebMarch: 1.44 in precipitation 1.4 MarApril: 2.82 in precipitation 2.8 AprMay: 3.83 in precipitation 3.8 MayJune: 4.01 in precipitation 4.0 JunJuly: 3.84 in precipitation 3.8 JulAugust: 3.29 in precipitation 3.3 AugSeptember: 3.21 in precipitation 3.2 SepOctober: 2.22 in precipitation 2.2 OctNovember: 1.07 in precipitation 1.1 NovDecember: 0.42 in precipitation 0.4 Dec

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

Nearby ZIP codes

All 8 nearest ZIP codes share zone 5a.

513435a
Greenville, IA · 9 mi
510475a
Peterson, IA · 9 mi
513015a
Spencer, IA · 9 mi
513385a
Everly, IA · 10 mi
510335a
Linn Grove, IA · 10 mi
510585a
Sutherland, IA · 11 mi
513465a
Hartley, IA · 12 mi
505855a
Sioux Rapids, IA · 12 mi

Iowa planting zones →

Questions about 51357

What planting zone is ZIP code 51357?

ZIP code 51357 (Royal, IA) is in USDA hardiness zone 5a on the 2023 map: the coldest night of an average winter reaches −20 to −15 °F (−28.9 to −26.1 °C).

When is the last frost in Royal, IA?

The median last spring frost (32 °F) near 51357 is May 2; after May 15 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Spencer Municipal Airport station.

When is the first frost in Royal, IA?

The median first fall frost near 51357 is October 2, giving a median frost-free growing season of 154 days.

When should I plant tomatoes in 51357?

Start tomato seeds indoors around Mar 7 – Mar 21 and set transplants outside around May 9 – May 23, one to three weeks after the median last frost.

How much rain and snow does 51357 get?

About 26.8 inches of precipitation a year (NOAA 1991–2020 normals, Spencer Municipal Airport station).

How hot do summers get in Royal, IA?

The average high peaks at 85 °F in July, with about 19 days a year at 90 °F or more.

What kind of soil does 51357 have?

The USDA soil survey maps McCreath at the center of ZIP 51357: silty clay loam, somewhat poorly drained, pH about 6.5 (neutral).

Did spring come early in Royal, IA in 2026?

Spring leaf-out near 51357 came on Mar 25 in 2026, 18 days earlier than the 1991–2020 average (Apr 12), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Royal, IA?

Long-day onions: the longest day near 51357 is 15 h 22 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).