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

Planting zone for 20842 — Dickerson, MD

ZIP code 20842 (Dickerson, Montgomery County) is in USDA zone 7b: the coldest winter night averages 5 to 10 °F. The median last spring frost is April 14 and the first fall frost October 29.

Where ZIP 20842 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 14

First frostOct 29

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 Dickerson, 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 Dickerson, MD

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostApril 14median — 50% chance of a later frost

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

First fall frostOctober 29median — 10% chance by Oct 13

Growing season196 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 2 and returns around November 8.

From the NOAA station Damascus 3 Ssw, MD — 11 miles away, elevation 699 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 20842

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Mar 3 – Mar 17

SpinachSow outdoors · Mar 3 – Mar 24

Broccoli, cabbageStart indoors · Feb 3 – Feb 17

Broccoli, cabbageTransplant · Mar 24 – Apr 7

Onion setsPlant outdoors · Mar 17 – Mar 31

PotatoesPlant outdoors · Mar 24 – Apr 7

LettuceSow outdoors · Mar 17 – Mar 31

Carrots, beetsSow outdoors · Mar 24 – Apr 7

TomatoesStart indoors · Feb 17 – Mar 3

TomatoesTransplant · Apr 21 – May 5

Peppers, eggplantStart indoors · Feb 3 – Feb 17

Peppers, eggplantTransplant · Apr 28 – May 12

BeansSow outdoors · Apr 21 – May 5

Sweet cornSow outdoors · Apr 21 – May 5

Cucumbers, squashSow outdoors · Apr 21 – May 5

Fall lettuce, spinachSow outdoors · Sep 3 – Sep 17

GarlicPlant cloves · Oct 15 – Nov 19

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 14) and first fall frost (Oct 29) 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 20842 came on Mar 12 — 6 days earlier than the 1991–2020 average (Mar 18).

average
Mar 182026
Mar 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 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 Dickerson, MD.

Soil in Dickerson, MD

The soil mapped at the center of ZIP 20842 is Brinklow — channery silt loam, well drained.

TextureChannery silt loama good balance for most vegetables

pH5.3strongly acidic; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter2%moderate

Hydrologic groupCwater soaks in slowly

Farmland classFarmland of statewide importanceUSDA classification

Map unit: Brinklow-Blocktown channery silt loams, 3 to 8 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 20842; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Dickerson, MD

Summer high84 °Faverage high, July

Winter low25 °Faverage low, January

Hot days13days a year at 90 °F or more

Freezing nights98nights a year at 32 °F or less

Growing degree days3,528base 50 °F — the season’s usable heat

Longest day14 h 56 mindaylight on June 21

Shortest day9 h 24 mindaylight on December 21

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

Precipitation47.9 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: Damascus 3 Ssw, MD (11 mi away); precipitation: Poolesville 0.4 Se, MD (4 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

208397b

Beallsville, MD · 2 mi

208387a

Barnesville, MD · 3 mi

208417b

Boyds, MD · 5 mi

208377b

Poolesville, MD · 6 mi

Germantown, MD · 8 mi

Maryland planting zones →

Questions about 20842

What planting zone is ZIP code 20842?

ZIP code 20842 (Dickerson, 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 Dickerson, MD?

The median last spring frost (32 °F) near 20842 is April 14; after May 2 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Damascus 3 Ssw station.

When is the first frost in Dickerson, MD?

The median first fall frost near 20842 is October 29, giving a median frost-free growing season of 196 days.

When should I plant tomatoes in 20842?

Start tomato seeds indoors around Feb 17 – Mar 3 and set transplants outside around Apr 21 – May 5, one to three weeks after the median last frost.

How much rain and snow does 20842 get?

About 47.9 inches of precipitation a year (NOAA 1991–2020 normals, Poolesville 0.4 Se station).

How hot do summers get in Dickerson, MD?

The average high peaks at 84 °F in July, with about 13 days a year at 90 °F or more.

What kind of soil does 20842 have?

The USDA soil survey maps Brinklow at the center of ZIP 20842: channery silt loam, well drained, pH about 5.3 (strongly acidic).

Did spring come early in Dickerson, MD in 2026?

Spring leaf-out near 20842 came on Mar 12 in 2026, 6 days earlier than the 1991–2020 average (Mar 18), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Dickerson, MD?

Intermediate onions: the longest day near 20842 is 14 h 56 min, so day-neutral types bulb best; long-day varieties may not bulb fully.

Did the zone for 20842 change?

Yes. The 2012 USDA map put 20842 in zone 7a; the 2023 map puts it in zone 7b. The newer map uses 1991–2020 data and more weather stations.