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

Planting zone for 29920 — Saint Helena Island, SC

ZIP code 29920 (Saint Helena Island, Beaufort County) is in USDA zone 9b: the coldest winter night averages 25 to 30 °F. The median last spring frost is March 3 and the first fall frost December 9.

Where ZIP 29920 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.

Zone9b25 to 30 °F

Coldest night−3.9 to −1.1 °C

Last frostMar 3

First frostDec 9

2012 zone8b

Was 8b on the 2012 map — a full zone warmer now. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 9b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Saint Helena Island, SC…

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 Helena Island, SC

JanFebMarAprMayJunJulAugSepOctNovDec

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

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

Safe for tender plantsMarch 20only 10% chance of frost after

First fall frostDecember 9median — 10% chance by Nov 21

Growing season282 daysfrost-free, median

A hard freeze (28 °F) usually ends around February 9 and returns around December 28.

From the NOAA station Beaufort Wwtp, SC — 9 miles away, elevation 26 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 29920

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Jan 20 – Feb 3

SpinachSow outdoors · Jan 20 – Feb 10

Broccoli, cabbageStart indoors · Dec 23 – Jan 6

Broccoli, cabbageTransplant · Feb 10 – Feb 24

Onion setsPlant outdoors · Feb 3 – Feb 17

PotatoesPlant outdoors · Feb 10 – Feb 24

LettuceSow outdoors · Feb 3 – Feb 17

Carrots, beetsSow outdoors · Feb 10 – Feb 24

TomatoesStart indoors · Jan 6 – Jan 20

TomatoesTransplant · Mar 10 – Mar 24

Peppers, eggplantStart indoors · Dec 23 – Jan 6

Peppers, eggplantTransplant · Mar 17 – Mar 31

BeansSow outdoors · Mar 10 – Mar 24

Sweet cornSow outdoors · Mar 10 – Mar 24

Cucumbers, squashSow outdoors · Mar 10 – Mar 24

Fall lettuce, spinachSow outdoors · Oct 14 – Oct 28

GarlicPlant cloves · Nov 25 – Dec 30

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Mar 3) and first fall frost (Dec 9) 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 29920 came on Feb 5 — 7 days later than the 1991–2020 average (Jan 29).

average
Jan 292026
Feb 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 9b in South Carolina

581 plants native to the lower 48 states, recorded in South Carolina, and rated by the USDA to survive 25 °F or colder — the bottom of zone 9b. 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 Saint Helena Island, SC.

Soil in Saint Helena Island, SC

The soil mapped at the center of ZIP 29920 is Chipley — fine sand, somewhat poorly drained.

TextureFine sanddrains and warms fast; dries out and needs more feeding

pH4.8strongly acidic; most vegetables like 6.0–7.0

DrainageSomewhat poorly drainedconsider raised beds

Organic matter1%low — add compost

Hydrologic groupAwater soaks in fast

Farmland classPrime farmland if irrigatedUSDA classification

Map unit: Seabrook fine sand.

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 29920; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Saint Helena Island, SC

Summer high91 °Faverage high, July

Winter low41 °Faverage low, January

Hot days58days a year at 90 °F or more

Freezing nights13nights a year at 32 °F or less

Growing degree days6,719base 50 °F — the season’s usable heat

Longest day14 h 17 mindaylight on June 21

Shortest day10 h 01 mindaylight on December 21

Onions to growShort-daysummer days stay under about 14 h 20 min, so long-day varieties won’t bulb

Precipitation45 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: Beaufort Wwtp, SC (9 mi away); precipitation: Beaufort Mcas, SC (12 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

299019a

Beaufort, SC · 4 mi

299389a

Hilton Head Island, SC · 7 mi

Port Royal, SC · 8 mi

299059a

Parris Island, SC · 9 mi

South Carolina planting zones →

Questions about 29920

What planting zone is ZIP code 29920?

ZIP code 29920 (Saint Helena Island, SC) is in USDA hardiness zone 9b on the 2023 map: the coldest night of an average winter reaches 25 to 30 °F (−3.9 to −1.1 °C).

When is the last frost in Saint Helena Island, SC?

The median last spring frost (32 °F) near 29920 is March 3; after March 20 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Beaufort Wwtp station.

When is the first frost in Saint Helena Island, SC?

The median first fall frost near 29920 is December 9, giving a median frost-free growing season of 282 days.

When should I plant tomatoes in 29920?

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

How much rain and snow does 29920 get?

About 45 inches of precipitation a year (NOAA 1991–2020 normals, Beaufort Mcas station).

How hot do summers get in Saint Helena Island, SC?

The average high peaks at 91 °F in July, with about 58 days a year at 90 °F or more.

What kind of soil does 29920 have?

The USDA soil survey maps Chipley at the center of ZIP 29920: fine sand, somewhat poorly drained, pH about 4.8 (strongly acidic).

Did spring come early in Saint Helena Island, SC in 2026?

Spring leaf-out near 29920 came on Feb 5 in 2026, 7 days later than the 1991–2020 average (Jan 29), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Saint Helena Island, SC?

Short-day onions: the longest day near 29920 is 14 h 17 min, so summer days stay under about 14 h 20 min, so long-day varieties won’t bulb.

Did the zone for 29920 change?

Yes. The 2012 USDA map put 29920 in zone 8b; the 2023 map puts it in zone 9b. The newer map uses 1991–2020 data and more weather stations.