{"schema":"askedwell-answer-v1","url":"https://askedwell.com/pages/how-long-does/start-seeds-before-last-frost","question":"How long before the last frost should you start seeds indoors?","short_answer":"Most vegetables are started indoors 4–10 weeks before your area's average last frost date: tomatoes 6–8 weeks, peppers and eggplant 8–10, broccoli and cabbage 4–6, onions and leeks 10–12. Fast growers like squash and cucumbers need only 2–4 weeks — or direct sowing.","long_answer":"**The system: count backwards from your last frost date**\n\nIndoor seed starting is a backwards-counting exercise. Find your area's **average last spring frost date**, then subtract each crop's recommended head start. Start too early and you get leggy, root-bound transplants that stall after planting; too late and you lose weeks of harvest.\n\nYour last frost date comes from your local cooperative extension service or a frost-date lookup (they interpolate NOAA climate-normal data by zip code). Remember it's an average — a roughly 50/50 gamble — so tender crops go out a week or two after it, not on it.\n\n**The head-start table (university extension consensus)**\n\n| Crop | Start indoors before last frost | Transplant outside |\n|---|---|---|\n| Onions, leeks | 10–12 weeks | 2–4 weeks BEFORE last frost (hardy) |\n| Peppers, eggplant | 8–10 weeks | 1–2 weeks AFTER last frost |\n| Tomatoes | 6–8 weeks | 1–2 weeks after last frost |\n| Broccoli, cabbage, cauliflower, kale | 4–6 weeks | 2–4 weeks before last frost (hardy) |\n| Lettuce | 4–6 weeks | around last frost, or direct sow |\n| Basil | ~6 weeks | after all frost danger |\n| Squash, cucumbers, melons | 2–4 weeks | 1–2 weeks after last frost — or direct sow |\n\n**Skip the indoor start entirely for:** beans, peas, corn, carrots, beets, radishes, turnips. These either dislike root disturbance or grow so fast that direct sowing wins.\n\n**Why the ranges differ so much**\n\nSlow, heat-loving crops (peppers, eggplant) germinate slowly and grow slowly — they need the long runway. Cucurbits (squash, cucumbers) do the opposite: they germinate in days, grow explosively, and sulk when their roots are disturbed, so a big transplant is a WORSE transplant. Onions from seed are simply slow to reach plantable size.\n\n**Germination temperature is the hidden variable**\n\nSeeds don't count days; they integrate soil temperature:\n\n- Most vegetables germinate well at **65–75°F (18–24°C)** soil temperature\n- Peppers and tomatoes prefer **75–85°F (24–29°C)** — on a cool windowsill, pepper germination can stretch from 8 days to 3+ weeks\n- A seedling heat mat under the tray solves this for the warm-lovers; remove it after germination\n\n**Light: the step most beginners under-do**\n\nA sunny window is usually not enough in late winter — seedlings stretch toward the glass and go leggy. The extension-service standard: bright light 12–16 hours/day, positioned a few inches above the canopy. This is the single biggest difference between stocky transplants and floppy ones.\n\n**Hardening off: the mandatory final week**\n\nIndoor seedlings have never met wind or direct sun. **Harden off over 7–14 days**: an hour or two of sheltered outdoor time, increasing daily, before transplanting. Skipping this step sunburns and wind-whips transplants — the classic \"my seedlings died the week I planted them\" cause.\n\n**A worked example**\n\nAverage last frost May 10:\n\n- Feb 15–Mar 1 → start onions/leeks\n- Mar 8–22 → start peppers/eggplant (on a heat mat)\n- Mar 22–Apr 5 → start tomatoes\n- Apr 5–12 → start broccoli/cabbage; transplant them out ~Apr 19–26\n- Apr 26 → start squash/cucumbers in pots (or direct sow May 17–24)\n- May 17–24 → transplant tomatoes, peppers, squash","ranges":[{"condition":"Onions, leeks","duration":"10–12 weeks before last frost"},{"condition":"Peppers, eggplant","duration":"8–10 weeks before"},{"condition":"Tomatoes","duration":"6–8 weeks before"},{"condition":"Broccoli, cabbage, kale, lettuce","duration":"4–6 weeks before"},{"condition":"Squash, cucumbers, melons","duration":"2–4 weeks before (or direct sow)"},{"condition":"Beans, peas, corn, root vegetables","duration":"Direct sow — no indoor start"}],"variables":[{"name":"Your last frost date","effect":"The anchor for every count-back. It is an AVERAGE — half of years frost later. Tender transplants go out 1–2 weeks after it, hardy brassicas 2–4 weeks before it"},{"name":"Soil temperature at germination","effect":"Peppers at 60°F soil: 3 weeks to germinate. At 80°F: about a week. A thermostat heat mat compresses the calendar for warm-season crops"},{"name":"Light quantity","effect":"12–16 hours of close, bright light makes stocky transplants; a window alone in Feb–Mar usually makes leggy ones that transplant poorly"},{"name":"Container size","effect":"Seedlings held too long in small cells go root-bound and stall for weeks after transplant — the reason \"earlier is better\" is false"},{"name":"Hardening off","effect":"The 7–14 day gradual outdoor transition. Skipping it costs more plants than any timing mistake"}],"sources":[{"label":"University of Minnesota Extension — Starting seeds indoors","tier":1,"note":"Extension-service head-start table, germination temperatures, hardening-off protocol"},{"label":"Old Farmer's Almanac — Frost dates lookup (NOAA climate normals)","tier":2,"url":"https://www.almanac.com/gardening/frostdates","note":"Zip-code average first/last frost dates interpolated from NOAA station data"},{"label":"USDA Plant Hardiness Zone Map","tier":1,"url":"https://planthardiness.ars.usda.gov/","note":"Zone context for variety selection (zones rate winter lows, not frost dates — use both)"}],"faq":[{"question":"What does my USDA zone tell me about seed starting?","answer":"Less than people think — zones rate average winter minimum temperatures, useful for choosing perennials and varieties. Your seed-starting calendar hangs on the last FROST date, a different dataset. Use zone for what to grow, frost date for when."},{"question":"Can I just start everything earlier to get a head start?","answer":"No — oversized indoor seedlings go root-bound, leggy, and stall after transplant. Field trials repeatedly show right-sized transplants catch up to and outproduce overgrown ones."},{"question":"Do I really need a grow light?","answer":"For February–March starts at most latitudes, yes — window light is too weak and too angled. Bright light 12–16 h/day kept a few inches above seedlings is the standard for stocky transplants."},{"question":"What if a frost is forecast after I transplant?","answer":"Cover transplants overnight with frost cloth (row cover), buckets, or cloches — a few degrees of protection is usually enough for a radiation frost. Uncover in the morning."}],"keywords":["when to start seeds indoors","seed starting calendar","last frost date","start tomato seeds","start pepper seeds","hardening off seedlings","germination temperature","grow lights for seedlings"],"category":"home-garden","date_published":"2026-07-16","date_modified":"2026-07-16","license":"CC-BY-4.0","attribution":"https://askedwell.com"}