Seed Starting Calculator
Type your ZIP code or city. You'll get the dates to sow 14 vegetables and herbs indoors, when to start hardening them off, and when to plant them outside, all counted back from your local last frost date.
- NOAA 1991–2020 frost dates
- UNH and UMN Extension timings
- Most US ZIP codes
2 Your seed-starting dates
Pick a place to updateExample: Plano, TX (75024). Search above for your own place.
Counted back from the average last frost for Plano, TX (75024) (NOAA station Richardson, 6.5 mi away).
| Crop | Sow indoors | Weeks indoors | Start hardening off | Plant outside |
|---|---|---|---|---|
| Onions (from seed) | Nov 29 (the year before) – Dec 13 (the year before) | 8–10 | Jan 24 | Feb 7 |
| Cabbage | Dec 27 (the year before) – Jan 10 | 4–6 | Jan 24 | Feb 7 |
| Kale | Dec 27 (the year before) – Jan 10 | 4–6 | Jan 24 | Feb 7 |
| Broccoli | Dec 27 (the year before) – Jan 24 | 4–6 | Jan 24 | Feb 7 – Feb 21 |
| Lettuce | Jan 3 – Jan 17 | 4–5 | Jan 24 | Feb 7 – Feb 14 |
| Cauliflower | Jan 10 – Jan 24 | 4–6 | Feb 7 | Feb 21 |
| Peppers | Jan 10 – Jan 24 | 8–10 | Mar 7 | Mar 21 |
| Eggplant | Jan 10 – Jan 31 | 8–10 | Mar 7 | Mar 21 – Mar 28 |
| Tomatoes | Jan 17 – Feb 7 | 6–8 | Feb 28 | Mar 14 – Mar 21 |
| Basil | Jan 24 – Feb 7 | 6–8 | Mar 7 | Mar 21 |
| Cucumbers | Feb 14 – Feb 28 | 3–4 | Feb 28 | Mar 14 – Mar 21 |
| Squash and zucchini | Feb 21 – Feb 28 | 3–4 | Mar 7 | Mar 21 |
| Pumpkins and winter squash | Feb 21 – Feb 28 | 3–4 | Mar 7 | Mar 21 |
| Melons | Feb 21 – Feb 28 | 3–4 | Mar 7 | Mar 21 |
Indoor weeks and planting-out times from UNH Cooperative Extension; hardening off starts two weeks before planting out (University of Minnesota Extension). Cool crops go out before the last frost; warm crops after it. If late frosts are common where you are, plant warm crops after Mar 29, the 1-in-10 date.
Quick answer
Start tomato seeds indoors 6 to 8 weeks before you plant them out, which extension guides time for 1 to 2 weeks after your average last frost. In Plano, Texas, where the average last frost is March 7, that means sowing tomatoes between January 17 and February 7. Onions go first, 12 to 14 weeks before the last frost.
Weeks indoors and when to plant out
| Crop | Weeks indoors | Plant outside | Sow indoors |
|---|---|---|---|
| Onions (from seed) | 8–10 | 4 wk before | 12–14 wk before last frost |
| Cabbage | 4–6 | 4 wk before | 8–10 wk before last frost |
| Kale | 4–6 | 4 wk before | 8–10 wk before last frost |
| Broccoli | 4–6 | 2–4 wk before | 6–10 wk before last frost |
| Lettuce | 4–5 | 3–4 wk before | 7–9 wk before last frost |
| Cauliflower | 4–6 | 2 wk before | 6–8 wk before last frost |
| Peppers | 8–10 | 2 wk after | 6–8 wk before last frost |
| Eggplant | 8–10 | 2–3 wk after | 5–8 wk before last frost |
| Tomatoes | 6–8 | 1–2 wk after | 4–7 wk before last frost |
| Basil | 6–8 | 2 wk after | 4–6 wk before last frost |
| Cucumbers | 3–4 | 1–2 wk after | 1–3 wk before last frost |
| Squash and zucchini | 3–4 | 2 wk after | 1–2 wk before last frost |
| Pumpkins and winter squash | 3–4 | 2 wk after | 1–2 wk before last frost |
| Melons | 3–4 | 2 wk after | 1–2 wk before last frost |
Weeks are counted from your average last frost. Use the calculator above for your own dates.
How the dates are worked out
Seed-starting dates come from two numbers: when a crop can go outside, and how many weeks it needs indoors before then. UNH Cooperative Extension's method is to pick the planting-out date first and count back.
- Find your last frost date. The calculator uses the average date from the nearest NOAA weather station, or the safer 1-in-10 date if you choose it.
- Find the planting-out date. Cool crops like cabbage and broccoli go out about 2 to 4 weeks before the last frost. Tomatoes, peppers and squash wait 1 to 2 weeks after it (eggplant up to 3).
- Count back the weeks indoors. Tomatoes need 6 to 8 weeks; peppers and eggplant 8 to 10; cucumbers, squash and melons only 3 to 4.
Worked example: Plano, Texas
Plano's average last frost is March 7. Tomatoes go out 1 to 2 weeks later, Mar 14 to Mar 21. Counting back 8 and 6 weeks puts the sowing window at Jan 17 to Feb 7. Peppers go out a little later than tomatoes but need 2 more weeks indoors, so they're sown earlier: Jan 10 to Jan 24. Hardening off starts two weeks before each crop goes out: Feb 28 for the tomatoes.
Don't start too early
It's tempting to sow in midwinter, but UNH Extension warns that seedlings started too early will probably be in poor health by the time you can plant them. If the dates above are still weeks away, wait.
Tips for healthy seedlings
These come from the University of Minnesota Extension's guide to starting seeds indoors:
- Sow at the right depth. A seed goes about twice as deep as it is wide.
- Keep it warm. Keep the air above 60°F. The potting mix can run up to 5°F cooler than the room.
- Give plenty of light. Seedlings need about 12 to 16 hours of light a day with a dark period at night. Keep grow lights no more than 4 inches above the tops; 2 inches is ideal.
- Harden them off. Two weeks before planting out, set seedlings outside for a few hours in afternoon shade, out of the wind. Give them a little more time and sun each day, and bring them in before cold nights.
Want the full season, including crops you sow straight into the ground and a fall planting plan? The frost dates tool has both.
Frequently asked questions
When should I start tomato seeds indoors?
Six to eight weeks before you plant them out. UNH Extension sets tomatoes out 1 to 2 weeks after the average last frost, so sow them 4 to 7 weeks before that frost date.
When should I start pepper seeds indoors?
Peppers need 8 to 10 weeks indoors and go out about 2 weeks after the average last frost, so sow them 6 to 8 weeks before the last frost date.
How long should I harden off seedlings?
About 2 weeks. The University of Minnesota Extension suggests starting with a few hours in afternoon shade, out of the wind, and adding time and sun each day.
Which seeds should not be started indoors?
Colorado State Extension sows peas, beans, sweet corn, carrots, beets and spinach straight into the garden. Their dates are in the frost dates tool's planting calendar.
Last reviewed 2026-10-24. See how we calculate for our sources and assumptions.