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

Planting zone for 20686 — Saint Marys City, MD

ZIP code 20686 (Saint Marys City, 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 30 and the first fall frost November 14.

Where ZIP 20686 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 30

First frostNov 14

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 Saint Marys City, 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 Saint Marys City, MD

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMarch 30median — 50% chance of a later frost

Safe for tender plantsApril 11only 10% chance of frost after

First fall frostNovember 14median — 10% chance by Oct 29

Growing season229 daysfrost-free, median

A hard freeze (28 °F) usually ends around March 19 and returns around November 29.

From the NOAA station St Inigoes Webster Nolf, MD — 3 miles away, elevation 20 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 20686

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Feb 16 – Mar 2

SpinachSow outdoors · Feb 16 – Mar 9

Broccoli, cabbageStart indoors · Jan 19 – Feb 2

Broccoli, cabbageTransplant · Mar 9 – Mar 23

Onion setsPlant outdoors · Mar 2 – Mar 16

PotatoesPlant outdoors · Mar 9 – Mar 23

LettuceSow outdoors · Mar 2 – Mar 16

Carrots, beetsSow outdoors · Mar 9 – Mar 23

TomatoesStart indoors · Feb 2 – Feb 16

TomatoesTransplant · Apr 6 – Apr 20

Peppers, eggplantStart indoors · Jan 19 – Feb 2

Peppers, eggplantTransplant · Apr 13 – Apr 27

BeansSow outdoors · Apr 6 – Apr 20

Sweet cornSow outdoors · Apr 6 – Apr 20

Cucumbers, squashSow outdoors · Apr 6 – Apr 20

Fall lettuce, spinachSow outdoors · Sep 19 – Oct 3

GarlicPlant cloves · Oct 31 – Dec 5

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Mar 30) and first fall frost (Nov 14) 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 20686 came on Mar 10 — 5 days later than the 1991–2020 average (Mar 5).

average
Mar 52026
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 Saint Marys City, MD.

Soil in Saint Marys City, MD

The soil mapped at the center of ZIP 20686 is Sassafras — sandy loam, well drained.

TextureSandy loamdrains and warms fast; dries out and needs more feeding

pH6.3slightly acidic; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter1.75%low — add compost

Hydrologic groupBwater soaks in moderately

Farmland classFarmland of statewide importanceUSDA classification

Map unit: Sassafras sandy loam, 5 to 10 percent slopes, Northern Coastal Plain.

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 20686; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Saint Marys City, MD

Summer high87 °Faverage high, July

Winter low30 °Faverage low, January

Hot days29days a year at 90 °F or more

Freezing nights69nights a year at 32 °F or less

Growing degree days4,397base 50 °F — the season’s usable heat

Longest day14 h 49 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: St Inigoes Webster Nolf, MD (3 mi away); precipitation: Park Hall 0.2 Sw, MD (2 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 8a.

Lexington Park, MD · 3 mi

206928a

Valley Lee, MD · 4 mi

206848a

Saint Inigoes, MD · 4 mi

206348a

Great Mills, MD · 5 mi

Maryland planting zones →

Questions about 20686

What planting zone is ZIP code 20686?

ZIP code 20686 (Saint Marys City, 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 Saint Marys City, MD?

The median last spring frost (32 °F) near 20686 is March 30; after April 11 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, St Inigoes Webster Nolf station.

When is the first frost in Saint Marys City, MD?

The median first fall frost near 20686 is November 14, giving a median frost-free growing season of 229 days.

When should I plant tomatoes in 20686?

Start tomato seeds indoors around Feb 2 – Feb 16 and set transplants outside around Apr 6 – Apr 20, one to three weeks after the median last frost.

How much rain and snow does 20686 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 Saint Marys City, MD?

The average high peaks at 87 °F in July, with about 29 days a year at 90 °F or more.

What kind of soil does 20686 have?

The USDA soil survey maps Sassafras at the center of ZIP 20686: sandy loam, well drained, pH about 6.3 (slightly acidic).

Did spring come early in Saint Marys City, MD in 2026?

Spring leaf-out near 20686 came on Mar 10 in 2026, 5 days later than the 1991–2020 average (Mar 5), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Saint Marys City, MD?

Intermediate onions: the longest day near 20686 is 14 h 49 min, so day-neutral types bulb best; long-day varieties may not bulb fully.

Did the zone for 20686 change?

Yes. The 2012 USDA map put 20686 in zone 7b; the 2023 map puts it in zone 8a. The newer map uses 1991–2020 data and more weather stations.