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When to Start Seeds Indoors in Zone 4

Start indoor, transplant, direct sow and fall dates for every crop in zones 4a and 4b, with their frost dates.

Tomato and pepper seedlings in trays under an LED grow light

Zone 4 frost dates

Median last spring and first fall frost dates for zone 4
Half-zoneLast spring frostFirst fall frostFrost-free days
AverageSaferSafestAverageSaferSafest
4a (-30 to -25°F)May 13May 18May 27Sep 28Sep 23Sep 15136
4b (-25 to -20°F)May 8May 14May 23Oct 1Sep 26Sep 18145

Medians across the ZIP codes in each half-zone, NOAA 1991 to 2020 climate normals. Average: half of years get frost past the date. Safer: 3 years in 10 (the Almanac's date). Safest: 1 year in 10.

When to start seeds in zone 4a

Counted from the average last frost, May 13, and the average first frost, Sep 28.

Planting dates for zone 4a at average frost dates
CropStart indoorsTransplantSow outdoorsFall sowing
BasilApr 1 to Apr 15May 13May 13·
Beet··Apr 29 to May 13by Aug 3
BroccoliApr 1 to Apr 15Apr 22 to Apr 29Apr 22 to Apr 29·
Brussels Sprouts···Jun 1
CabbageMar 4 to Mar 18Apr 22 to Apr 29Apr 22 to Apr 29·
Cantaloupe··May 20 to May 27·
Carrot··Apr 22 to Apr 29·
CauliflowerMar 11 to Mar 25Apr 29 to May 6Apr 29 to May 6·
CilantroApr 1 to Apr 15May 13May 13·
Collard Greens···Jun 29
Cucumber··May 13·
Dill··Apr 29 to May 6·
EggplantApr 1 to Apr 15May 27··
Green Beans··May 6 to May 13·
KaleFeb 25 to Mar 11Apr 8 to Apr 15Apr 8 to Apr 15Jun 29
LeekFeb 18 to Mar 4···
LettuceApr 1 to Apr 8May 13Apr 22 to Apr 29·
MarigoldApr 1 to Apr 15May 13May 13·
OnionMar 18 to Apr 1Apr 15 to Apr 29··
ParsleyApr 1May 13May 13·
Peas··Apr 15 to Apr 29Jul 27 to Aug 3
PepperMar 18 to Apr 1May 27··
Potato··Apr 22 to Apr 29·
Pumpkin··May 27·
Radish··Apr 15 to Apr 29·
SpinachApr 1 to Apr 8May 13Apr 15 to Apr 22·
Squash··May 13·
Sunflower··May 13·
Sweet Corn··May 13·
Swiss ChardApr 1 to Apr 8May 13Apr 15 to Apr 22·
TomatoMar 18 to Apr 1May 27··
Watermelon··May 20 to May 27·
ZinniaApr 15May 13May 13·
Zucchini··May 13·

When to start seeds in zone 4b

Counted from the average last frost, May 8, and the average first frost, Oct 1.

Planting dates for zone 4b at average frost dates
CropStart indoorsTransplantSow outdoorsFall sowing
BasilMar 27 to Apr 10May 8May 8·
Beet··Apr 24 to May 8by Aug 6
BroccoliMar 27 to Apr 10Apr 17 to Apr 24Apr 17 to Apr 24·
Brussels Sprouts···Jun 4
CabbageFeb 27 to Mar 13Apr 17 to Apr 24Apr 17 to Apr 24·
Cantaloupe··May 15 to May 22·
Carrot··Apr 17 to Apr 24·
CauliflowerMar 6 to Mar 20Apr 24 to May 1Apr 24 to May 1·
CilantroMar 27 to Apr 10May 8May 8·
Collard Greens···Jul 2
Cucumber··May 8·
Dill··Apr 24 to May 1·
EggplantMar 27 to Apr 10May 22··
Green Beans··May 1 to May 8·
KaleFeb 20 to Mar 6Apr 3 to Apr 10Apr 3 to Apr 10Jul 2
LeekFeb 13 to Feb 27···
LettuceMar 27 to Apr 3May 8Apr 17 to Apr 24·
MarigoldMar 27 to Apr 10May 8May 8·
OnionMar 13 to Mar 27Apr 10 to Apr 24··
ParsleyMar 27May 8May 8·
Peas··Apr 10 to Apr 24Jul 30 to Aug 6
PepperMar 13 to Mar 27May 22··
Potato··Apr 17 to Apr 24·
Pumpkin··May 22·
Radish··Apr 10 to Apr 24·
SpinachMar 27 to Apr 3May 8Apr 10 to Apr 17·
Squash··May 8·
Sunflower··May 8·
Sweet Corn··May 8·
Swiss ChardMar 27 to Apr 3May 8Apr 10 to Apr 17·
TomatoMar 13 to Mar 27May 22··
Watermelon··May 15 to May 22·
ZinniaApr 10May 8May 8·
Zucchini··May 8·

Your own schedule

Your location

Zone medians. Your ZIP code gives the dates of your nearest weather station.

Frost risk

Half of years still get a frost after the spring date, and half get the first fall frost before the fall date.

Frost dates at three risk levels
AverageSaferSafest
Last spring frostMay 13May 18May 27
First fall frostSep 28Sep 23Sep 15
Crops (8 selected)

Start your first seeds indoors

Mar 18onion, pepper, tomato

Average frost dates: last May 13, first Sep 28 (zone 4a).
Season
Spring seed starting schedule
CropStart indoorsHarden offTransplantSow outdoorsNotes
BasilVery tenderApr 1 to Apr 15Apr 22 to May 12May 13May 13Indoors 4 to 6 wk before last frost. Transplant at last frost. Sow outdoors at last frost. Sprouts in 5 to 14 days, best at 75 to 85°F soil. Pot up at the first true leaves.
BroccoliHardyApr 1 to Apr 15Apr 15 to Apr 21Apr 22 to Apr 29Apr 22 to Apr 29Indoors 4 to 6 wk before last frost. Transplant 2 to 3 wk before last frost. Sow outdoors 2 to 3 wk before last frost. Sprouts in 3 to 10 days, best at 80°F soil. Pot up at the first true leaves. The published dates leave little time indoors: sow at the early end.
CucumberTender···May 13Sow outdoors at last frost. Sprouts in 6 to 10 days, best at 60 to 95°F soil.
LettuceHardyApr 1 to Apr 8Apr 22 to May 12May 13Apr 22 to Apr 29Indoors 5 to 6 wk before last frost. Transplant at last frost. Sow outdoors 2 to 3 wk before last frost. Sprouts in 4 to 10 days, best at 40 to 80°F soil. Pot up at the first true leaves.
OnionHardyMar 18 to Apr 1Apr 1 to Apr 14Apr 15 to Apr 29·Indoors 6 to 8 wk before last frost. Transplant 2 to 4 wk before last frost. Sprouts in 7 to 12 days, best at 50 to 95°F soil. Pot up at the first true leaves.
PepperVery tenderMar 18 to Apr 1May 6 to May 26May 27·Indoors 6 to 8 wk before last frost. Transplant 2 wk after last frost. Sprouts in 10 to 20 days, best at 65 to 95°F soil. Pot up at the first true leaves.
SquashTender···May 13Sow outdoors at last frost. Sprouts in 3 to 12 days, best at 70 to 95°F soil.
TomatoVery tenderMar 18 to Apr 1May 6 to May 26May 27·Indoors 6 to 8 wk before last frost. Transplant 2 wk after last frost. Sprouts in 6 to 14 days, best at 60 to 85°F soil. Pot up at the first true leaves.

How to start seeds indoors

Light
Give seedlings 14 to 18 hours of light a day on a timer, with fluorescent or LED fixtures 2 to 6 in above the leaves. Raise the lights as the plants grow.
Clemson HGIC: 16 to 18 hours, tubes 2 to 4 in above. UMD Extension: 14 to 16 hours, 2 to 6 in.
Seed starting mix
Use a sterile, soilless mix, never garden soil. To mix your own, combine equal parts by volume of fine pine bark, sphagnum peat moss and perlite.
NC State Extension Gardener Handbook; Clemson HGIC.
Sowing and warmth
Sow two or three seeds per cell and keep the strongest seedling. A mix temperature of 65 to 75°F germinates most vegetables; after they sprout, 55 to 60°F nights and 65 to 70°F days keep them stocky.
UMD Extension.
Potting up
Move seedlings into larger pots shortly after the first true leaves appear, while they are small and recover quickly.
UMD Extension; Clemson HGIC (one or two sets of true leaves).
Hardening off
Start two to three weeks before transplanting, once plants are about 3 in tall: set them outdoors by day, bring them in before sundown, and give them more direct sun each day. Skip days below 45°F or with strong wind.
Clemson HGIC: 2 to 3 weeks. NC State: at least 2 weeks, not below 45°F.

Zone 4 frost dates

Zone 4 winters bottom out at -30 to -20°F. It is the first zone with a large sample: 772 ZIP codes in 4a and 1,205 in 4b. NOAA's 1991 to 2020 normals put the medians at:

  • Zone 4a: average last spring frost May 13, first fall frost Sep 28, and 136 frost-free days.
  • Zone 4b: average last spring frost May 8, first fall frost Oct 1, and 145 frost-free days.

The two halves differ by only 5 days in spring and 3 in fall, so one calendar serves most of zone 4. Your own station can easily differ from the median by more than that.

When to start seeds indoors in zone 4

Count back from the last frost:

Start indoors = last frost date − weeks indoors

  • Leeks come first, at 10 to 12 weeks: Feb 18 to Mar 4 in 4a and Feb 13 to Feb 27 in 4b.
  • Kale follows at 9 to 11 weeks, from late February.
  • Tomatoes, peppers and onions all take 6 to 8 weeks, so they share one sowing window: Mar 18 to Apr 1 in 4a and Mar 13 to Mar 27 in 4b. That makes mid-March the busiest week of the year for a zone 4 seed shelf.

Onions go out early, 2 to 4 weeks before the frost: Apr 15 to Apr 29 in 4a. Tomatoes and peppers wait until 2 weeks after it: May 27 in 4a and May 22 in 4b.

Frost risk matters more here

Zone 4 springs are long and uncertain. In 4a:

  • The safer date (3 years in 10 get a later frost) is May 18.
  • The safest date (1 year in 10) is May 27.

For tomatoes, that moves transplanting to Jun 1 at the safer setting and Jun 10 at the safest.

Even at the safest dates, zone 4 still fits the long crops. In 4a, peppers set out on Jun 10 have 97 days before the safest first frost of Sep 15, against the 70 to 85 days they need from transplanting. Watermelons sown outdoors have 104 days against 85. The calculator flags no crop as too slow in either half of zone 4, but the margin for peppers is two weeks at most. Start them at the early end of the window and pick varieties on the short side.

Fall crops in zone 4

The first frost arrives in late September, so fall crops are sown in early summer. At average dates in 4a:

  • Brussels sprouts are sown by Jun 1.
  • Kale and collards are sown by Jun 29.
  • Fall peas go in Jul 27 to Aug 3.
  • The last beet sowing is Aug 3.

Zone 4b is 3 days later for each.

Next steps

Enter your ZIP code in the planner below for the dates of your nearest weather station. Neighboring calendars: zone 3 and zone 5.