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When should you start your seeds?
Choose your USDA zone and get a personalised sowing calendar for 20 popular crops — start-indoors dates, transplant or direct-sow dates, and expected harvest windows. No sign-up, no submit button.
Your zone
Typical last spring frost for the selected zone: 20 Apr.
Your seed-starting calendar
Every date below is counted from your zone’s average last frost (20 Apr). “Start indoors” is the sowing window under cover; the third column is when seedlings or seeds go into the garden.
| Crop | Start indoors | Transplant / sow outdoors | Expected harvest |
|---|
Harvest windows assume typical “days to maturity” — counted from transplanting for indoor-started crops and from sowing for direct-sown crops — and average weather. Cool, cloudy seasons run late; warm ones run early.
How this is calculated
Like a lab worksheet — here is every step, so you can check the working:
- Last frost date: each zone maps to a typical average last spring frost (table below). Zone 6 → 20 April.
- Start indoors:
last frost − (weeks × 7 days)— e.g. tomatoes at 6–8 weeks before a 20 April frost → 24 Feb–9 Mar. - Transplant / sow outdoors:
last frost + offset— e.g. peppers 2 weeks after → 4 May; peas 4–6 weeks before → 9–23 Mar. - Harvest window:
outdoor date + days to maturity— counted from transplanting for indoor-started crops, from sowing for direct-sown ones.
Zone frost dates used here
| USDA zone | Typical last spring frost |
|---|---|
| Zone 3 | 15 May |
| Zone 4 | 10 May |
| Zone 5 | 30 Apr |
| Zone 6 | 20 Apr |
| Zone 7 | 10 Apr |
| Zone 8 | 20 Mar |
| Zone 9 | 15 Feb |
| Zone 10 | 30 Jan* |
*Many zone 10 gardens rarely see frost at all — treat the date as a cool-season planning anchor. All dates are representative long-term averages; see the note above about verifying locally.
Sources & assumptions
Zone frost dates are representative averages compiled from the USDA Plant Hardiness Zone Map and published frost-date tables (Old Farmer’s Almanac methodology and cooperative extension 30-year climate normals). They smooth over elevation, large water bodies and urban heat islands. Crop timing ranges — weeks before or after last frost, and days to maturity — follow US cooperative extension planting calendars (including Cornell and University of Georgia) and standard seed-catalogue guidance. Weeks are counted as full 7-day weeks. Harvest windows are estimates, not guarantees: weather rules.
Want the full explanation?
How last frost dates are set, why starting too early backfires, and how to harden seedlings off — in plain language, with zone tables you can print.
Seed starting calendar FAQ
What exactly is a “last frost date”?
It is the average date of the last spring frost (0°C / 32°F), computed from about 30 years of weather records. Roughly half of years will see frost after that date, so treat it as a planning anchor — and keep frost cloth handy for tender transplants.
My town’s published date differs from my zone’s. Which do I trust?
Trust the local one. A USDA zone averages a huge area; your county’s cooperative extension service publishes frost dates for nearby weather stations, which reflect your elevation and microclimate far better. Use this tool’s date as a starting point only.
What happens if I start seeds too early?
Usually nothing good: leggy, weak seedlings starved of light, and warm-season crops like peppers stalling in cold soil. A smaller transplant set out into warm soil almost always overtakes a big, stressed one set out early.
Can I just direct-sow everything?
You can for the seven direct-sow crops in the table (peas, beans, carrots and the rest). But tomatoes, peppers and eggplant need the indoor head start in zones 3–7 — direct-sown, they simply run out of warm season before ripening.
Does this calendar work for autumn planting?
Not directly. Autumn sowing counts backwards from your first autumn frost, not forwards from the last spring one. Use the same crop timing ranges, but anchor them to the autumn date from your extension service.