Zone 4b Planting Schedule: Short-Season Vegetable Calendar

June 12, 2026

Zone 4b averages a last spring frost of May 10–20 and a first fall frost of September 1–10, leaving 100–115 frost-free days. Every crop decision in this zone comes down to one number: days to maturity against that hard September deadline.

Browse the GardeningByZone regional books for zone-matched planting guides built around these same frost windows.

Zone 4b at a Glance

Metric	Value
Last spring frost (avg)	May 10–20
First fall frost (avg)	September 1–10
Frost-free growing season	100–115 days
Ground workable (spring)	Late April
Min soil temp for warm-season transplants	60°F

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Month-by-Month Planting Calendar

February: Start Tomatoes, Peppers, and Leeks

Indoors at 70°F, 10–12 weeks before a May 15 target transplant date.

• Tomatoes (10 weeks out: start February 28–March 7)
• Peppers (12 weeks out: start February 14–21; soil 75–80°F for germination)
• Leeks (10–12 weeks)

Pepper germination drops below 60% at soil temperatures under 70°F. A heat mat is not optional for Zone 4b February starts.

March: Brassicas, Onions, and Celery

Indoors, 6–8 weeks before last frost.

• Broccoli
• Cauliflower
• Cabbage
• Onions (from seed; bulbing types need 10–12 weeks to reach transplant size)
• Celery (slow to germinate; start the first week of March)

See the seed starting timing guide for count-back calculations from your specific last frost date.

April: First Direct Sows

Direct sow outdoors as soon as the ground is workable, typically the last 2 weeks of April for most Zone 4b locations.

Crop	Min Soil Temp	Ideal Soil Temp
Peas	35°F	45–55°F
Spinach	35°F	45°F
Lettuce	35°F	60–65°F
Kale	40°F	60–65°F
Radishes	40°F	55–65°F
Carrots	40°F	60–70°F
Beets	50°F	60–65°F

Peas germinate at 35°F but slowly (10–14 days). Soil at 50°F cuts that to 6–8 days with no loss of stand.

Also in April: start cucumbers, squash, and melons indoors 3–4 weeks before last frost. Starting earlier risks root-bound transplants at planting time.

May 1–14: Harden Off and Cold-Tolerant Transplants

Warm-season crops stay inside until mid-May. Use this window to:

1. Harden off tomato and pepper starts over 7–10 days of gradual outdoor exposure.
2. Direct sow a second succession of lettuce and spinach.
3. Transplant broccoli, cabbage, and cauliflower (hardened starts tolerate light frost).
4. Set out onion seedlings once soil hits 50°F.
5. Pre-warm beds for squash and cucumbers with black plastic mulch.

May 15–31: Last Frost Window Clears

Soil temperature matters more than the calendar here. These are minimums at the 2-inch depth, not air temperature:

Crop	Min Soil Temp
Beans (direct sow)	60°F
Corn (direct sow)	60°F
Cucumbers	60°F
Tomatoes	60°F
Summer squash	60°F
Peppers	65°F
Melons	65°F

Cold soil stunts peppers for the entire season. A soil thermometer delivers a more reliable read than any forecast.

Direct sow: beans, corn.

Transplant outdoors: tomatoes, peppers, eggplant, cucumbers, summer squash, winter squash, melons.

June and July: Succession Planting into Cleared Beds

Spring crops begin bolting in late June. When peas finish and lettuce goes bitter, pull them and resow into the cleared space:

• Beans (second succession, June 1–15)
• Beets (for fall harvest; 55–65 days to maturity)
• Carrots (for fall harvest; sow by June 20 for most 70-day varieties)

August: Last Window for Fall Crops

The first fall frost arrives September 1–10. Count back from that date using days-to-maturity plus 7–10 days of germination time.

Crop	Days to Maturity	Last Safe Direct Sow
Radishes	25–30	August 10
Spinach	40–45	July 20
Lettuce, leaf	45–55	July 15
Kale	50–65	July 1
Beets	55–65	June 28

A row cover or cold frame extends these dates by 2–4 weeks and makes Zone 4b fall gardening viable well into October.

Variety Selection for a Short Season

Zone 4b requires short-season varieties across warm-season crops. Day counts below are from transplant for starts, from direct sow for beans and corn.

• Tomatoes: 60–70 days (Stupice, Siletz, Glacier)
• Peppers: 60–70 days (Ace, Gypsy, Mohawk)
• Winter squash: 80–95 days (Delicata, Sweet Dumpling)
• Melons: 70–80 days (Collective Farm Woman, Minnesota Midget)
• Corn: 60–75 days (Early Sunglow, Sundance)

Avoid varieties described as “90 days from direct sow.” Those are calibrated for Zone 6 and warmer, and will not reach maturity before frost in Zone 4b.

Microclimate Adjustments

Zone 4b spans from the Adirondacks to the Montana Rockies. A gardener at 800 feet in Vermont and one at 4,500 feet in Wyoming share a zone designation but may have a 10–14 day difference in usable frost-free days.

Check Zone 4b local frost data for city-level averages rather than relying on regional means.

Tracking Crops for Zone 4b Efficiency

Log these data points each season for any crop you grow from transplant: the transplant date and soil temperature that day, the first harvest date, and the date of first fall frost in your specific yard.

Lettuce is worth tracking closely in Zone 4b. The bolt window typically runs 6–8 weeks after transplant, earlier in a hot June. Once you know your average bolt date, you can time the spring sow backward and the fall sow forward from the center of summer, reliably hitting harvest windows on both ends.

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