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

Planting zone for 20620 — Callaway, MD

ZIP code 20620 (Callaway, St. Mary's County) is in USDA zone 8a: the coldest winter night averages 10 to 15 °F. The median last spring frost is March 22 and the first fall frost November 26.

Where ZIP 20620 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.

Zone8a10 to 15 °F

Coldest night−12.2 to −9.4 °C

Last frostMar 22

First frostNov 26

2012 zone7b

Was 7b 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 8a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Callaway, MD…

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 Callaway, MD

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMarch 22median — 50% chance of a later frost

Safe for tender plantsApril 5only 10% chance of frost after

First fall frostNovember 26median — 10% chance by Nov 10

Growing season248 daysfrost-free, median

A hard freeze (28 °F) usually ends around March 10 and returns around December 9.

From the NOAA station Solomons, MD — 7 miles away, elevation 13 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 20620

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Feb 8 – Feb 22

SpinachSow outdoors · Feb 8 – Mar 1

Broccoli, cabbageStart indoors · Jan 11 – Jan 25

Broccoli, cabbageTransplant · Mar 1 – Mar 15

Onion setsPlant outdoors · Feb 22 – Mar 8

PotatoesPlant outdoors · Mar 1 – Mar 15

LettuceSow outdoors · Feb 22 – Mar 8

Carrots, beetsSow outdoors · Mar 1 – Mar 15

TomatoesStart indoors · Jan 25 – Feb 8

TomatoesTransplant · Mar 29 – Apr 12

Peppers, eggplantStart indoors · Jan 11 – Jan 25

Peppers, eggplantTransplant · Apr 5 – Apr 19

BeansSow outdoors · Mar 29 – Apr 12

Sweet cornSow outdoors · Mar 29 – Apr 12

Cucumbers, squashSow outdoors · Mar 29 – Apr 12

Fall lettuce, spinachSow outdoors · Oct 1 – Oct 15

GarlicPlant cloves · Nov 12 – Dec 17

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Mar 22) and first fall frost (Nov 26) 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 20620 came on Mar 10 — about the same time as the 1991–2020 average (Mar 8).

average
Mar 82026
Mar 10

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 8a in Maryland

629 plants native to the lower 48 states, recorded in Maryland, and rated by the USDA to survive 10 °F or colder — the bottom of zone 8a. 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 Callaway, MD.

Soil in Callaway, MD

The soil mapped at the center of ZIP 20620 is Leonardtown — silt loam, poorly drained.

TextureSilt loama good balance for most vegetables

pH4.3strongly acidic; most vegetables like 6.0–7.0

DrainagePoorly drainedconsider raised beds

Organic matter5.2%high

Hydrologic groupDwater soaks in very slowly

Farmland classNot prime farmlandUSDA classification

Map unit: Leonardtown silt 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 20620; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Callaway, MD

Summer high88 °Faverage high, July

Winter low30 °Faverage low, January

Hot days31days a year at 90 °F or more

Freezing nights59nights a year at 32 °F or less

Growing degree days4,559base 50 °F — the season’s usable heat

Longest day14 h 50 mindaylight on June 21

Shortest day9 h 30 mindaylight on December 21

Onions to growIntermediateday-neutral types bulb best; long-day varieties may not bulb fully

Precipitation46.9 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: Solomons, MD (7 mi away); precipitation: Park Hall 0.2 Sw, MD (4 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

206348a

Great Mills, MD · 1 mi

206928a

Valley Lee, MD · 4 mi

206197b

California, MD · 4 mi

206678a

Park Hall, MD · 4 mi

206538a

Lexington Park, MD · 5 mi

206908a

Tall Timbers, MD · 5 mi

206868a

Saint Marys City, MD · 6 mi

206308a

Drayden, MD · 6 mi

Maryland planting zones →

Questions about 20620

What planting zone is ZIP code 20620?

ZIP code 20620 (Callaway, MD) is in USDA hardiness zone 8a on the 2023 map: the coldest night of an average winter reaches 10 to 15 °F (−12.2 to −9.4 °C).

When is the last frost in Callaway, MD?

The median last spring frost (32 °F) near 20620 is March 22; after April 5 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Solomons station.

When is the first frost in Callaway, MD?

The median first fall frost near 20620 is November 26, giving a median frost-free growing season of 248 days.

When should I plant tomatoes in 20620?

Start tomato seeds indoors around Jan 25 – Feb 8 and set transplants outside around Mar 29 – Apr 12, one to three weeks after the median last frost.

How much rain and snow does 20620 get?

About 46.9 inches of precipitation a year (NOAA 1991–2020 normals, Park Hall 0.2 Sw station).

How hot do summers get in Callaway, MD?

The average high peaks at 88 °F in July, with about 31 days a year at 90 °F or more.

What kind of soil does 20620 have?

The USDA soil survey maps Leonardtown at the center of ZIP 20620: silt loam, poorly drained, pH about 4.3 (strongly acidic).

Did spring come early in Callaway, MD in 2026?

Spring leaf-out near 20620 came on Mar 10 in 2026, about the same as the 1991–2020 average (Mar 8), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Callaway, MD?

Intermediate onions: the longest day near 20620 is 14 h 50 min, so day-neutral types bulb best; long-day varieties may not bulb fully.

Did the zone for 20620 change?

Yes. The 2012 USDA map put 20620 in zone 7b; the 2023 map puts it in zone 8a. The newer map uses 1991–2020 data and more weather stations.