USDA zone 6a in Maryland
USDA plant hardiness zone 6a covers 3 locations across Maryland (average annual extreme minimum −10 to −5 °F): Midlothian, MD, Mountain Lake Park, MD, Swanton, MD. Average last spring frost across this group ranges April 29 (Midlothian) to May 6 (Mountain Lake Park), and growing seasons run 156–174 days (Mountain Lake Park to Swanton) — even within one state, because hardiness sets winter survival, not planting dates. The table below gives every Maryland location's own frost dates; the printable planting calendar uses Midlothian, this group's median-season location.
- USDA zone
- 6a−10 to −5 °F
- Last frost range
- Apr 29–May 6avg, 32°F
- First frost range
- Oct 9–Oct 20avg, 32°F
- Growing season range
- 156–174days
Locations in this group
Every location below shares this zone and a nearby weather station, but keeps its own frost dates — find your town for its own numbers, or use the ZIP planner on the home page for an instant personalized answer.
| Location | Also covers | Nearest station | Last frost | First frost | Season (days) |
|---|---|---|---|---|---|
| Midlothian * | Lonaconing | Frostburg 2 | Apr 29 | Oct 18 | 171 |
| Mountain Lake Park | Accident | Oakland 1 Se | May 6 | Oct 9 | 156 |
| Swanton | Jennings, Kitzmiller | Savage Rvr Dam | Apr 29 | Oct 20 | 174 |
* Midlothian is this group's median-season location — the calendar below is computed from its data.
Data: NOAA NCEI U.S. Climate Normals 1991–2020 (public domain) and USDA Plant Hardiness Zone Map 2023. Planting windows synthesized from U.S. Cooperative Extension guides.
Planting calendar (Midlothian, representative)
Computed from Midlothian's average frost dates — the median-season location in this Marylandzone 6a group. hatched = start seeds indoors, solid green = plant out, teal = a fall sowing, and the terracotta dot marks the estimated first harvest. Ranges are extension-guide planning guidance, not guarantees — your own location's dates may run a week or two earlier or later (see the table above).
- Start indoors
- Plant out
- Fall sowing
- First harvest
| Crop | Frost tolerance | Start indoors | Plant out | First harvest | Fall planting | Season fit |
|---|---|---|---|---|---|---|
| Tomato | Tender | Mar 4 – Mar 18 | May 6 – May 13 | Jul 5 – Jul 25 | — | matures comfortably |
| Pepper | Very tender | Feb 18 – Mar 4 | May 13 – May 20 | Jul 12 – Aug 11 | — | matures comfortably |
| Cucumber | Tender | Apr 1 – Apr 8 | May 6 – May 13 | Jun 25 – Jul 15 | — | matures comfortably |
| Summer squash / zucchini | Tender | — | May 6 – May 13 | Jun 20 – Jul 5 | — | matures comfortably |
| Bush bean | Tender | — | May 6 – May 13 | Jun 25 – Jul 5 | Aug 19 – Aug 29 | matures comfortably |
| Sweet corn | Tender | — | Apr 29 – May 13 | Jun 28 – Jul 28 | — | matures comfortably |
| Basil | Very tender | Mar 18 – Apr 1 | May 6 – May 13 | Jun 5 – Jun 20 | — | matures comfortably |
| Lettuce | Half-hardy | Mar 18 – Apr 1 | Apr 1 – Apr 15 | May 16 – May 31 | Aug 5 – Aug 20 | matures comfortably |
| Pea | Hardy | — | Mar 18 – Apr 1 | May 12 – May 27 | Jul 26 – Aug 10 | matures comfortably |
| Spinach | Hardy | — | Mar 18 – Apr 1 | Apr 27 – May 7 | Aug 15 – Aug 25 | matures comfortably |
| Carrot | Half-hardy | — | Apr 8 – Apr 15 | Jun 7 – Jun 27 | Jul 16 – Aug 5 | matures comfortably |
| Broccoli | Half-hardy | Mar 4 – Mar 18 | Apr 1 – Apr 15 | May 26 – Jun 15 | Jul 21 – Aug 10 | matures comfortably |
Which crops fit this growing season
Using Midlothian's own 171-day growing season (32°F, NOAA 1991–2020 median) against each crop's real days-to-maturity range: 12 of 12 crops mature here with comfortable margin. A different location in the table above with a longer or shorter season will get a different mix — the ZIP planner on the home page gives your own.
Frost & freeze dates (Midlothian)
From NOAA's 1991–2020 Climate Normals at station USC00183415. The median (p50) is the average date; the 90%-safe column is the date the freeze has passed in about 9 years out of 10 — the conservative date to plant after or harvest before.
| Threshold | Last spring — avg | Last spring — 90%-safe | First fall — avg | First fall — 90%-safe | Season (days) |
|---|---|---|---|---|---|
| 36°F | May 9 | May 26 | Oct 7 | Oct 20 | 150 |
| 32°F (freeze) | Apr 29 | May 15 | Oct 18 | Nov 1 | 171 |
| 28°F | Apr 17 | May 6 | Oct 29 | Nov 13 | 196 |
| 24°F | Apr 5 | Apr 20 | Nov 9 | Nov 26 | 218 |
Growing degree days
Growing degree days (GDD) accumulate warmth above a base temperature over the year — a better predictor of crop development than the calendar alone. This group's median GDD (base 50°F) across all 3 locations is 2,642; Midlothian's own reading is shown below.
| Model | °F·days | Used for |
|---|---|---|
| Base 50°F (warm-season) | 2,508 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 4,645 | cool-season crops (brassicas, greens) |
Hardiness zone 6a in Maryland
Zone 6a means an average annual extreme minimum winter temperature of about −10 to −5 °F on the USDA's 2023 map — the number that tells you which perennials, shrubs, and trees reliably survive an average winter here. It does not set your planting dates, which come from the frost calendar above. Maryland spans 5 hardiness zones in this dataset — see all Maryland locations for the full range, including zones6b, 7a, 7b, 8a.
Explore zone 6a in other states at zone 6a, or see all USDA hardiness zones.
Frequently asked questions
- What does USDA hardiness zone 6a mean in Maryland?
- Zone 6a means an average annual extreme minimum winter temperature of −10 to −5 °F — the standard USDA measure of which perennials survive winter. 3 locations in Maryland fall in this zone. It does not set planting dates; see the frost calendar below for that.
- Where in Maryland's zone 6a is the growing season longest?
- Swanton runs the longest season on this page at about 174 days; Mountain Lake Park is shortest at about 156 days — they share the same hardiness zone, but they sit at different weather stations, so their frost calendars differ.
- When should I plant tomatoes in Maryland's zone 6a?
- Using Midlothian's frost dates (this page's median-season location): start seeds indoors about Mar 4 – Mar 18, then transplant outside about May 6 – May 13. Your own location in the table above may differ by a week or two — use the ZIP planner on the home page for your exact station's dates.
- Does every location in Maryland's zone 6a have the same frost dates?
- No — they do not all share a weather station, so frost dates vary by a week or more across the 3 locations listed (see the table above for each location's own dates).
Sources & method
Frost, freeze, growing-season, and growing-degree-day figures are NOAA NCEI U.S. Climate Normals 1991–2020, one reading per location's own nearest station (see the table above). The hardiness zone is the USDA Plant Hardiness Zone Map 2023, matched to each location's ZIP. Planting windows are computed by counting from the average last and first frost using per-crop offsets synthesized from U.S. Cooperative Extension guides — the full method and citations are on the methodology page.