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

Planting zone for 20646 — La Plata, MD

ZIP code 20646 (La Plata, Charles County) is in USDA zone 7b: the coldest winter night averages 5 to 10 °F. The median last spring frost is April 17 and the first fall frost October 27.

Where ZIP 20646 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.

Zone7b5 to 10 °F

Coldest night−15 to −12.2 °C

Last frostApr 17

First frostOct 27

2012 zone7a

Was 7a 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 7b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for La Plata, 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 La Plata, MD

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostApril 17median — 50% chance of a later frost

Safe for tender plantsMay 2only 10% chance of frost after

First fall frostOctober 27median — 10% chance by Oct 12

Growing season195 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 2 and returns around November 6.

From the NOAA station Mechanicsville 5 Ne, MD — 15 miles away, elevation 102 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 20646

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Mar 6 – Mar 20

SpinachSow outdoors · Mar 6 – Mar 27

Broccoli, cabbageStart indoors · Feb 6 – Feb 20

Broccoli, cabbageTransplant · Mar 27 – Apr 10

Onion setsPlant outdoors · Mar 20 – Apr 3

PotatoesPlant outdoors · Mar 27 – Apr 10

LettuceSow outdoors · Mar 20 – Apr 3

Carrots, beetsSow outdoors · Mar 27 – Apr 10

TomatoesStart indoors · Feb 20 – Mar 6

TomatoesTransplant · Apr 24 – May 8

Peppers, eggplantStart indoors · Feb 6 – Feb 20

Peppers, eggplantTransplant · May 1 – May 15

BeansSow outdoors · Apr 24 – May 8

Sweet cornSow outdoors · Apr 24 – May 8

Cucumbers, squashSow outdoors · Apr 24 – May 8

Fall lettuce, spinachSow outdoors · Sep 1 – Sep 15

GarlicPlant cloves · Oct 13 – Nov 17

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 17) and first fall frost (Oct 27) 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 20646 came on Mar 10 — 3 days later than the 1991–2020 average (Mar 7).

average
Mar 72026
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 7b in Maryland

618 plants native to the lower 48 states, recorded in Maryland, and rated by the USDA to survive 5 °F or colder — the bottom of zone 7b. 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 La Plata, MD.

Soil in La Plata, MD

The soil mapped at the center of ZIP 20646 is Issue — silt loam, somewhat poorly drained.

TextureSilt loama good balance for most vegetables

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

DrainageSomewhat poorly drainedconsider raised beds

Organic matter5%high

Hydrologic groupB/Dmoderate when drained; wet otherwise

Farmland classNot prime farmlandUSDA classification

Map unit: Issue silt loam, occasionally flooded.

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 20646; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in La Plata, MD

Summer high85 °Faverage high, July

Winter low25 °Faverage low, January

Hot days16days a year at 90 °F or more

Freezing nights98nights a year at 32 °F or less

Growing degree days3,649base 50 °F — the season’s usable heat

Longest day14 h 51 mindaylight on June 21

Shortest day9 h 28 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: Mechanicsville 5 Ne, MD (15 mi away); precipitation: Port Tobacco Village 1.0 S, MD (2 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 7b.

206047b

Waldorf, MD · 1 mi

206777b

Port Tobacco, MD · 3 mi

White Plains, MD · 5 mi

Maryland planting zones →

Questions about 20646

What planting zone is ZIP code 20646?

ZIP code 20646 (La Plata, MD) is in USDA hardiness zone 7b on the 2023 map: the coldest night of an average winter reaches 5 to 10 °F (−15 to −12.2 °C).

When is the last frost in La Plata, MD?

The median last spring frost (32 °F) near 20646 is April 17; after May 2 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Mechanicsville 5 Ne station.

When is the first frost in La Plata, MD?

The median first fall frost near 20646 is October 27, giving a median frost-free growing season of 195 days.

When should I plant tomatoes in 20646?

Start tomato seeds indoors around Feb 20 – Mar 6 and set transplants outside around Apr 24 – May 8, one to three weeks after the median last frost.

How much rain and snow does 20646 get?

About 46.9 inches of precipitation a year (NOAA 1991–2020 normals, Port Tobacco Village 1.0 S station).

How hot do summers get in La Plata, MD?

The average high peaks at 85 °F in July, with about 16 days a year at 90 °F or more.

What kind of soil does 20646 have?

The USDA soil survey maps Issue at the center of ZIP 20646: silt loam, somewhat poorly drained, pH about 4.3 (strongly acidic).

Did spring come early in La Plata, MD in 2026?

Spring leaf-out near 20646 came on Mar 10 in 2026, 3 days later than the 1991–2020 average (Mar 7), according to the USA National Phenology Network Spring Index.

What kind of onions grow in La Plata, MD?

Intermediate onions: the longest day near 20646 is 14 h 51 min, so day-neutral types bulb best; long-day varieties may not bulb fully.

Did the zone for 20646 change?

Yes. The 2012 USDA map put 20646 in zone 7a; the 2023 map puts it in zone 7b. The newer map uses 1991–2020 data and more weather stations.