Frost dates for 21077Harmans, MD
The average last spring frost in Harmans is April 10 and the average first fall frost is October 31, giving a typical growing season of about 204 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Apr 10
- Average first fall frost
- Oct 31
- Growing season
- 204 days
Safer after Apr 25 (1-in-10 risk)
Possible by Oct 17 (1-in-10 risk)
Last frost typically in 158 days
Frost risk by date
NOAA reports frost dates as probabilities. The middle date is the average (a 50% chance). For spring, the 10% date is a safer planting date: frost after it happens in about 1 year in 10. Light frost (36°F) can damage tender plants; a hard freeze (28°F) kills most annuals.
| Temperature | Last spring: 90% / 50% / 10% chance | First fall: 10% / 50% / 90% chance | Growing season (50%) | Years with at least one |
|---|---|---|---|---|
| Light frost (36°F) | Apr 9 · Apr 24 · May 12 | Oct 8 · Oct 21 · Nov 2 | 179 days | 100% |
| Frost / freeze (32°F) | Mar 27 · Apr 10 · Apr 25 | Oct 17 · Oct 31 · Nov 12 | 204 days | 100% |
| Hard freeze (28°F) | Mar 13 · Mar 28 · Apr 10 | Oct 30 · Nov 10 · Nov 27 | 228 days | 100% |
Planting calendar for Harmans
Planting windows from the University of Maryland Extension calendar, shifted to your average frost dates. Use them as a starting point and adjust for seed packet instructions and local conditions.
| Crop | Task | Window |
|---|---|---|
| Tomatoes | Start seeds indoors | Mar 10 – May 16 |
| Tomatoes | Transplant outdoors | Apr 26 – Jul 11 |
| Peppers | Start seeds indoors | Mar 10 – Apr 10 |
| Peppers | Transplant outdoors | May 10 – Jun 10 |
| Eggplant | Start seeds indoors | Mar 27 – Apr 25 |
| Eggplant | Transplant outdoors | May 10 – Jun 10 |
| Cucumbers | Sow outdoors | May 10 – Jul 21 |
| Summer squash | Sow outdoors | Apr 26 – Jun 10 |
| Winter squash & pumpkins | Sow outdoors | May 10 – Jun 10 |
| Snap beans | Sow outdoors | Apr 26 – Aug 13 |
| Sweet corn | Sow outdoors | Apr 26 – Jul 11 |
| Watermelon & cantaloupe | Sow outdoors | May 10 – Jun 10 |
| Okra | Sow outdoors | May 3 – May 26 |
| Peas | Sow outdoors (spring) | Mar 10 – Apr 25 |
| Potatoes | Plant outdoors (spring) | Mar 10 – May 10 |
| Onions | Start seeds indoors (spring) | Jan 27 – Feb 23 |
| Onions | Transplant outdoors (spring) | Mar 27 – Apr 25 |
| Broccoli | Start seeds indoors (spring) | Feb 20 – Mar 26 |
| Broccoli | Transplant outdoors (spring) | Mar 27 – Apr 25 |
| Broccoli | Start seeds indoors (fall) | Jul 1 – Jul 11 |
| Broccoli | Transplant outdoors (fall) | Jul 31 – Aug 11 |
| Cabbage | Start seeds indoors (spring) | Feb 10 – Mar 10 |
| Cabbage | Transplant outdoors (spring) | Mar 10 – Apr 10 |
| Cabbage | Start seeds indoors (fall) | Jun 21 – Jul 21 |
| Cabbage | Transplant outdoors (fall) | Jul 21 – Aug 21 |
| Leaf lettuce | Sow outdoors (spring) | Mar 10 – May 26 |
| Leaf lettuce | Sow outdoors (fall) | Jul 21 – Sep 6 |
| Spinach | Sow outdoors (spring) | Mar 3 – Apr 16 |
| Spinach | Sow outdoors (fall) | Aug 7 – Sep 11 |
| Radishes | Sow outdoors (spring) | Mar 10 – Apr 30 |
| Radishes | Sow outdoors (fall) | Jul 21 – Sep 21 |
| Kale | Sow outdoors (spring) | Mar 27 – Apr 16 |
| Kale | Sow outdoors (fall) | Jul 14 – Aug 21 |
| Carrots | Sow outdoors (spring) | Apr 10 – May 26 |
| Carrots | Sow outdoors (fall) | Jun 21 – Aug 6 |
| Garlic | Plant outdoors (fall) | Oct 21 – Nov 21 |
Where these dates come from
ZIP code 21077 is matched to the NOAA station Baltimore Wash Intl Ap, MD, 1.7 km away, at 156 ft elevation (34 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Baltimore Wash Intl Ap, MD (used) | 156 ft | Apr 10 | Oct 31 |
| Md Sci Ctr Baltimore, MD | 20 ft | Mar 24 | Nov 21 |
| Laurel 3 W, MD | 400 ft | Apr 5 | Nov 9 |
| Cylburn, MD | 235 ft | Apr 2 | Nov 7 |
Frost dates near Harmans
- Hanover, MD 21076 · last Apr 10, first Oct 31
- Baltimore, MD 21240 · last Apr 10, first Oct 31
- Severn, MD 21144 · last Apr 10, first Oct 31
- Glen Burnie, MD 21061 · last Apr 10, first Oct 31
- Linthicum Heights, MD 21090 · last Apr 10, first Oct 31
- Fort George G Meade, MD 20755 · last Apr 10, first Oct 31
- Elkridge, MD 21075 · last Apr 10, first Oct 31
- Jessup, MD 20794 · last Apr 10, first Oct 31
Frequently asked questions
- When is the last frost in Harmans, MD?
- For ZIP code 21077, the average last spring frost (32°F) is April 10, based on NOAA 1991-2020 climate normals for the Baltimore Wash Intl Ap, MD weather station. There is a 1-in-10 chance of a frost after April 25.
- When is the first frost in Harmans, MD?
- The average first fall frost (32°F) is October 31. There is a 1-in-10 chance of frost by October 17, so tender plants are at risk from that point on.
- How long is the growing season in 21077?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 204 days long.
- Are these frost dates a forecast?
- No. They are 30-year averages and probabilities from NOAA weather station records. Use them to plan, then watch your local forecast before planting tender crops or leaving them uncovered.