When to Start Seeds Indoors in Zone 4
Your month-by-month seed-starting calendar, timed to a last frost around Early – mid May.
- Min Winter Temp
- -30 to -20 °F / -34 to -29 °C
- Last Spring Frost
- Early – mid May
- First Fall Frost
- Mid September – mid October
- Growing Season
- 120–150 days
- Annual Rainfall
- 20–45 in
Seed starting in Zone 4
Starting seeds indoors gives heat-loving crops the head start they need to ripen within Zone 4's season. Because everything is timed to your last spring frost — around Early – mid May in Zone 4 — the calendar below shows exactly which month to start each crop. Count back from your transplant date, sow under bright light, and harden seedlings off before they go outside.
Zone 4 seed-starting calendar
March
All March tasks →Start these indoors
Get a jump on the season under lights or on a sunny windowsill so transplants are ready when the weather warms.
Sow ⅛ in deep at 80°F on a heat mat. Slow to sprout (14–21 days) — start early.
Sow ¼ in deep at 80°F; needs steady warmth for 8 weeks indoors.
Sow ¼ in deep in trays; keep tops trimmed to 3 in for stocky transplants. Choose day-length type for your latitude.
Soak seed overnight; slow to germinate (3 weeks). Surface-sow under lights.
April
All April tasks →Start these indoors
Get a jump on the season under lights or on a sunny windowsill so transplants are ready when the weather warms.
Sow ¼ in deep in cell trays; keep at 70–75°F. Germinates in 7–10 days.
Tomatillos
Sow ¼ in deep at 70°F; treat like tomatoes.
Sow ¼ in deep; ready to transplant in 4–6 weeks at 4–5 in tall.
Sow ¼ in deep; harden off well before setting out.
Surface-sow under lights at 70°F; very frost-tender.
Sow ¼ in deep; quick and reliable from seed.
How to start seeds indoors
- 1
Count back from your last frost. Most warm-season crops start 6–8 weeks before; peppers and eggplant 8–10 weeks.
- 2
Sow into a clean seed-starting mix, at the depth on the packet, and keep it consistently warm (a heat mat speeds germination).
- 3
Give seedlings strong light as soon as they sprout — a sunny window is rarely enough; a shop light a few inches above works well.
- 4
Pot up if seedlings outgrow their cells before it’s warm enough to plant out.
- 5
Harden off over 7–10 days — gradually expose them to outdoor sun and wind — before transplanting after your last frost.
Seed starting in Zone 4: common questions
When should I start seeds indoors in Zone 4?＋
In Zone 4, the indoor-sowing months are March and April, timed to a last spring frost around Early – mid May. Start the longest-season crops first and quicker crops closer to your transplant date.
What seeds can I start indoors in Zone 4?＋
Common crops to start indoors in Zone 4 include Peppers, Eggplant, Onions, Parsley, Tomatoes, Tomatillos, Broccoli, Cabbage. Warm-season crops like tomatoes and peppers benefit most from an indoor head start.
How many weeks before the last frost should I start seeds in Zone 4?＋
It depends on the crop: peppers and eggplant want 8–10 weeks, tomatoes 6–8 weeks, and quicker crops like cucumbers or squash just 3–4 weeks before transplanting. Count back from Zone 4's last frost (around Early – mid May) to find each start date.
Zone 4 overview →
Frost dates, climate, and everything to grow here.
Monthly calendars →
What to sow, transplant, and harvest each month.
Plant growing guides →
Full care guides for every crop in the calendar.