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Frost dates and planting calendar for Rockville, Maryland

Updated October 30, 2026. Based on USDA, NOAA and Colorado State University Extension data. Published by Humblebee.

USDA hardiness zone
7b[1]
Median last spring frost
Apr 10[2]
Median first fall frost
Nov 1[3]
Growing season, median
202 days[4]

Rockville, Maryland is in USDA hardiness zone 7b on the 2023 map[1]. The median last spring frost at the NOAA Beltsville station is April 10, so in half of years the last frost comes after that date[2].

Frost dates

JanFebMarAprMayJunJulAugSepOctNovDecLast spring frost: 9 in 10 years after Mar 27, half of years Apr 10, 1 in 10 years after May 1Last frostmedian Apr 10First fall frost: 9 in 10 years before Nov 14, half of years Nov 1, 1 in 10 years before Oct 16First frostmedian Nov 1Frost riskHardyHardy vegetables: plant Mar 13 to Mar 27Mar 13 to Mar 27Semi-hardySemi-hardy vegetables: plant Mar 27 to Apr 10Mar 27 to Apr 10TenderTender vegetables: plant around Apr 10around Apr 10Very tenderVery tender vegetables: plant from Apr 24from Apr 24
Shaded: the span between the dates frost passes in 9 of 10 years and 1 of 10 years[2][3]. Green: planting windows from the CSU rules applied to the median last frost (GardenFacts calculation)[6]. Exact dates are in the tables below.

The frost dates here are odds, not a forecast. They come from NOAA climate normals for the Beltsville weather station, using records from 1991 to 2020[5]. In 9 of 10 years the last spring frost comes after March 27, and in 1 of 10 years it comes after May 1[2]. In the fall, the median first frost is November 1, and in 1 of 10 years the first frost comes before October 16[3]. Any single year can be earlier or later[2].

Frost Likely (9 in 10 years) Even odds (5 in 10) Unlikely (1 in 10)
Last spring frost (32°F)[2] after March 27 after April 10 after May 1
First fall frost (32°F)[3] before October 16 before November 1 before November 14
  • Hard freeze (28°F): median last spring date March 29, median first fall date November 11[7].
  • Frost-free growing season: at least 180 days in 9 of 10 years, 202 days in half of years and 221 days in 1 of 10 years[4].
  • The low reached 32°F or colder in 100% of years and 28°F or colder in 100% of years[8].
  • Weather station: Beltsville (USC00180700), 12.6 miles from the city center, 145 feet, 28 years of 1991 to 2020 records[5].

When to plant vegetables

Colorado State University Extension's planting guide was written for Colorado, so these dates are simple arithmetic and not local advice[6]. Hardy vegetables such as lettuce, peas and spinach can go in as early as 2 to 4 weeks before the median last frost, which is March 13 to March 27[6]. Semi-hardy vegetables such as carrots and potatoes can go in as early as 2 weeks before the median last frost, which is March 27[9]. Tender vegetables such as snap beans and sweet corn can be planted from seed around April 10[10]. Very tender vegetables such as tomatoes and peppers typically wait 2 or more weeks after the median last frost, so the earliest start is April 24[11].

  • Hardy (broccoli, cabbage, kohlrabi, lettuce, onions, peas, radishes, spinach, turnips): as early as 2 to 4 weeks before the median last frost (April 10) is March 13 to March 27[6]
  • Semi-hardy (beets, carrots, cauliflower, parsnips, potatoes, Swiss chard): as early as 2 weeks before the median last frost (April 10) is March 27, up to the median date itself[9]
  • Tender (snap beans, sweet corn, cucumbers, summer squash): from seed around the median last frost date, April 10[10]
  • Very tender (cantaloupe, eggplant, peppers, tomatoes, winter squash, watermelon): the earliest start, two weeks after the median last frost (April 10), is April 24[11]
Vegetable (CSU group) Plant from First harvest around
Broccoli (hardy)[12] Mar 13 May 17 (from transplants)
Cabbage (hardy)[12] Mar 13 Jun 6 (from transplants)
Kohlrabi (hardy)[12] Mar 13 May 2
Lettuce (hardy)[12] Mar 13 May 12
Onions (hardy)[12] Mar 13 Jul 1
Peas (hardy)[12] Mar 13 May 17
Radishes (hardy)[12] Mar 13 Apr 12
Spinach (hardy)[12] Mar 13 Apr 22
Turnips (hardy)[12] Mar 13 May 2
Beets (semi-hardy)[12] Mar 27 May 26
Carrots (semi-hardy)[12] Mar 27 Jun 5
Cauliflower (semi-hardy)[12] Mar 27 not listed
Parsnips (semi-hardy)[12] Mar 27 Jun 5
Potatoes (semi-hardy)[12] Mar 27 Jul 30
Swiss chard (semi-hardy)[12] Mar 27 May 26
Snap beans (tender)[12] Apr 10 Jun 9
Sweet corn (tender)[12] Apr 10 Jun 9
Cucumbers (tender)[12] Apr 10 Jun 4
Summer squash (tender)[12] Apr 10 May 30
Cantaloupe (very tender)[12] Apr 24 Jul 18
Eggplant (very tender)[12] Apr 24 Jun 23 (from transplants)
Peppers (very tender)[12] Apr 24 Jul 3 (from transplants)
Tomatoes (very tender)[12] Apr 24 Jun 28 (from transplants)
Winter squash (very tender)[12] Apr 24 Aug 2
Watermelon (very tender)[12] Apr 24 Jul 18
Spacing, depth and soil temperature (CSU Extension)
Vegetable Min. soil temp Depth Spacing Days to harvest
Broccoli[13] 40°F 1/2 in 18 in 65
Cabbage[13] 40°F 1/2 in 18 in 85
Kohlrabi[13] 40°F 1/2 in 7-9 in 50
Lettuce[13] 35°F 1/4 in 7-9 in 60
Onions[13] 35°F 1/4 in (seed), 1-2 in (sets) 4-6 in 110
Peas[13] 40°F 1 in 4-6 in 65
Radishes[13] 40°F 1/2 in 2-3 in 30
Spinach[13] 40°F 1/2 in 4-6 in 40
Turnips[13] 40°F 1/2 in 4-6 in 50
Beets[13] 40°F 3/4-1 in 4-6 in 60
Carrots[13] 40°F 1/4 in 2-3 in 70
Cauliflower[13] 40°F 1/2 in 18 in –
Parsnips[13] 35°F 1/2 in 5-6 in 70
Potatoes[13] 45°F – – 125
Swiss chard[13] 40°F 1 in 7-9 in 60
Snap beans[13] 55°F 1-1 1/2 in 6 in 60
Sweet corn[13] 50°F 1-1 1/2 in 12 x 30 in or 9 x 36 in 60-90
Cucumbers[13] 60°F 1 in 6 in trellised, 24-36 in untrellised 55
Summer squash[13] 60°F 1-1 1/2 in 36-48 in 50
Cantaloupe[13] 60°F 1-1 1/2 in 36-48 in 85
Eggplant[13] 60°F 1/4 in 18-24 in 60
Peppers[13] 60°F 1/4 in 15-18 in 70
Tomatoes[13] 50°F 1/4 in 24 in trellised 65
Winter squash[13] 60°F 1-1 1/2 in 36-48 in 100
Watermelon[13] 60°F 1-1 1/2 in 36-48 in 85

Hardiness zone

Zone 7b means the average coldest night of the year was 5°F to 10°F over 1991 to 2020[1]. The zone is about winter lows, not summer heat or frost dates[14]. All of Rockville's land area lies in ZIP code areas rated zone 7b[15].

Zone 7b: average annual extreme minimum temperature 5°F to 10°F (1991 to 2020)[1]. Modeled value at the city center: 6.9°F[1].

Share of the city's land area by ZIP code zone: zone 7b 100%[15].

All towns in zone 7b and what zone 7b means

Zone by ZIP code
ZIP code Zone Coldest night range
20850[15] 7b 5 to 10°F
20852[15] 7b 5 to 10°F
20851[15] 7b 5 to 10°F
20854[15] 7b 5 to 10°F
20853[15] 7b 5 to 10°F
20855[15] 7b 5 to 10°F
20877[15] 7b 5 to 10°F

Questions people ask

What growing zone is Rockville, Maryland?
The 2023 USDA map puts the center of Rockville in zone 7b[1]. By land area, 100% of the city lies in ZIP code areas rated 7b[15].
When is the last frost in Rockville?
The median last spring frost is April 10, so in half of years the last frost comes after that date[2]. In 1 of 10 years it comes after May 1[2].
When to plant tomatoes in Rockville?
CSU Extension typically says 2 or more weeks after the average last spring frost for tomatoes, which makes April 24 the earliest start using the median last frost[11]. The CSU guide was written for Colorado[11].
When is the first frost in Rockville?
The median first fall frost is November 1, so in half of years the first frost comes before that date[3]. In 1 of 10 years it comes before October 16[3].
How long is the growing season in Rockville?
The growing season is at least 202 days in half of years[4]. It is at least 180 days in 9 of 10 years[4].

Facts and sources

  1. The 2023 USDA Plant Hardiness Zone Map puts the center of Rockville, Maryland in zone 7b. Zone 7b means an average annual extreme minimum temperature of 5°F to 10°F over 1991 to 2020. The map's modeled value at the city center is 6.9°F. USDA zone map 2023 (PRISM, OSU)
  2. Last spring frost (32°F) at this station: in 9 of 10 years the last frost comes after March 27, in half of years after April 10, and in 1 of 10 years after May 1 (NOAA 1991 to 2020 normals). The median last frost date is April 10. NOAA Climate Normals 1991-2020
  3. First fall frost (32°F) at this station: in 1 of 10 years the first frost comes before October 16, in half of years before November 1, and in 9 of 10 years before November 14 (NOAA 1991 to 2020 normals). The median first frost date is November 1. NOAA Climate Normals 1991-2020
  4. Growing season (days between the last spring and first fall 32°F frost) at this station: at least 180 days in 9 of 10 years, at least 202 days in half of years, and at least 221 days in 1 of 10 years. NOAA Climate Normals 1991-2020
  5. Frost dates on this page come from NOAA climate normals for the Beltsville weather station (USC00180700), 12.6 miles from the center of Rockville at 145 feet, using 28 years of records from 1991 to 2020. NOAA Climate Normals 1991-2020
  6. Colorado State University Extension's vegetable planting guide (written for Colorado) groups broccoli, cabbage, kohlrabi, lettuce, onions, peas, radishes, spinach, turnips as hardy vegetables, with this rule: as early as 2-4 weeks before the average last... CSU Extension GardenNotes #720
  7. Hard freeze (28°F) at this station: the median last spring date is March 29 and the median first fall date is November 11. NOAA Climate Normals 1991-2020
  8. At this station the low reached 32°F or colder in 100% of years from 1991 to 2020, and 28°F or colder in 100% of years. NOAA Climate Normals 1991-2020
  9. Colorado State University Extension's vegetable planting guide (written for Colorado) groups beets, carrots, cauliflower, parsnips, potatoes, Swiss chard as semi-hardy vegetables, with this rule: as early as 0-2 weeks before the average last spring frost.... CSU Extension GardenNotes #720
  10. Colorado State University Extension's vegetable planting guide (written for Colorado) groups snap beans, sweet corn, cucumbers, summer squash as tender vegetables, with this rule: from seed around the average last spring frost; cucumber and summer squash... CSU Extension GardenNotes #720
  11. Colorado State University Extension's vegetable planting guide (written for Colorado) groups cantaloupe, eggplant, peppers, tomatoes, winter squash, watermelon as very tender vegetables, with this rule: typically 2 or more weeks after the average last... CSU Extension GardenNotes #720
  12. GardenFacts calculation: earliest planting date plus CSU days to harvest (table on this page), from the station's median last frost. NOAA Climate Normals 1991-2020
  13. CSU Extension vegetable table: soil temperature, depth, spacing, days to harvest (table on this page). CSU Extension GardenNotes #720
  14. USDA hardiness zones are based on the average annual extreme minimum winter temperature (the coldest night of each winter, averaged over 1991 to 2020 for the 2023 map), not on summer heat or frost dates. Each zone spans 10°F and each half zone (a or b)... USDA Plant Hardiness Zone Map
  15. Rockville, Maryland overlaps 7 ZIP code areas. By land area, 100% lies in ZIP code areas rated zone 7b. USDA zone map 2023 (PRISM, OSU)

Frost dates are probabilities from 1991 to 2020 weather records at one NOAA station, not a forecast. Any year can be earlier or later. The hardiness zone describes the average coldest winter night, not frost dates or summer heat. Spots inside the city can differ (ZIP table). Planting rules come from Colorado State University Extension's guide, written for Colorado. A local extension office may give dates tuned to the area. Planting and harvest dates marked GardenFacts calculation are simple arithmetic from the facts above, not advice from the source.

Hardiness zone data: USDA Plant Hardiness Zone Map (2023), USDA Agricultural Research Service and PRISM Group, Oregon State University, prism.oregonstate.edu, accessed October 30, 2026. This is not the official USDA map. Frost data: NOAA NCEI U.S. Climate Normals 1991-2020. Planting rules: Colorado State University Extension.