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    Free guide · USDA zones 3–10

    When to plant onion 🧅

    Onion takes 90–120 days to mature, spaced 4" apart at 0.25" deep. Start indoors and transplant for the longest harvest.

    Planting dates by USDA zone

    ZoneStart indoorsDirect sowTransplantHarvest
    Zone 3March 2 – March 16April 27 – May 11April 27 – May 11August 31 – September 28
    Zone 4February 21 – March 6April 17 – May 1April 17 – May 1August 21 – September 18
    Zone 5February 7 – February 21April 3 – April 17April 3 – April 17August 7 – September 4
    Zone 6January 22 – February 5March 18 – April 1March 18 – April 1July 22 – August 19
    Zone 7January 8 – January 22March 4 – March 18March 4 – March 18July 8 – August 5
    Zone 8December 22 – January 5February 16 – March 1February 16 – March 1June 21 – July 19
    Zone 9November 23 – December 7January 18 – February 1January 18 – February 1May 23 – June 20
    Zone 10November 7 – November 21January 2 – January 16January 2 – January 16May 7 – June 4

    Dates are averages — adjust ±1–2 weeks for your microclimate. Need your exact dates? Enter your zip code below.

    Get your personalized onion planting dates

    Care tips

    • Match variety to your latitude (long/short day).
    • Stop watering when tops fall over.
    • Cure in a dry, shaded spot for 2 weeks before storing.

    Good companions

    Carrot, Beet, Lettuce.

    Read more: Companion planting chart for vegetables

    Track your onion harvest with BotaNotes

    Log planting dates, get AI-powered care reminders, and journal every harvest. Free 15-day trial.

    Frequently asked questions

    When should I start onion seeds indoors in zone 5?▾

    In USDA zone 5, start onion seeds indoors between February 7 and February 21 — that's 10–12 weeks before the average last frost (May 1).

    When should I start onion seeds indoors in zone 6?▾

    In USDA zone 6, start onion seeds indoors between January 22 and February 5 — that's 10–12 weeks before the average last frost (April 15).

    When should I start onion seeds indoors in zone 7?▾

    In USDA zone 7, start onion seeds indoors between January 8 and January 22 — that's 10–12 weeks before the average last frost (April 1).

    When should I start onion seeds indoors in zone 8?▾

    In USDA zone 8, start onion seeds indoors between December 22 and January 5 — that's 10–12 weeks before the average last frost (March 15).

    When can I transplant onion seedlings outdoors?▾

    Transplant onion seedlings about -4–-2 weeks after your average last spring frost. In zone 6 that's around March 18–April 1.

    How long does onion take to grow?▾

    Onion typically takes 90–120 days to mature, with harvest beginning roughly 14–18 weeks after the last spring frost.

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