Seed Starting Date Calculator
Enter your last spring frost date and pick crops to get the date to start each indoors, the date to transplant, and the sowing date for direct-seeded crops, sorted into a calendar.
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Best for market gardeners, CSA growers, and home gardeners planning spring seeding. Updated .
Your frost date and crops
Custom crops
Your seed starting calendar
| Crop | Start indoors | Transplant | Direct sow |
|---|---|---|---|
| Onion (from seed) | Sat, February 13, 2027 | Sat, April 17, 2027 | n/a |
| Broccoli | Sat, March 27, 2027 | Sat, May 1, 2027 | n/a |
| Lettuce | Sat, March 27, 2027 | Sat, April 24, 2027 | n/a |
| Pepper | Sat, March 27, 2027 | Sat, May 29, 2027 | n/a |
| Tomato | Sat, April 10, 2027 | Sat, May 29, 2027 | n/a |
| Summer squash or zucchini | Sat, May 8, 2027 | Sat, May 29, 2027 | Sat, May 29, 2027 |
| Bean (direct sown) | n/a | n/a | Sat, May 15, 2027 |
Transplant date = last frost + weeks before or after. Start indoors = transplant date − weeks indoors. Direct sow = last frost + weeks before or after. Offsets follow the UNH Extension planting guide and are for spring planting; fall and soil-temperature crops are not scheduled here.
About the seed starting date calculator
Every seed packet says "start 6 to 8 weeks before your last frost," and every grower has to turn that into a date on a calendar, twenty times over. This calculator does the arithmetic. Enter your average last spring frost date, tick the crops you grow, and it returns the indoor seeding date, the transplant date, and, for direct-sown crops, the sowing date, sorted by when the work happens. Add custom crops with the weeks from your own packets.
The crop table comes from University of New Hampshire Extension's planting guide, which gives weeks from seed to transplant and when each crop is safe to set out relative to the last frost. It is a spring planner for frost-scheduled crops.
How the dates are built
The transplant date is last frost date + weeks before or after for that crop: cabbage and kale go out 4 weeks before, broccoli and cauliflower 2 weeks before, tomatoes and peppers 2 weeks after, eggplant 3 weeks after. The indoor seeding date is transplant date - weeks indoors, using the midpoint of the guide's range (6 to 8 weeks becomes 7). Direct-sown crops use last frost plus their offset: radish and turnip 2 weeks before, beans and parsnips after the frost date. Where the guide gives a range for setting out, the calculator uses the later, safer week.
Your frost date matters more than the table
Use the average last spring frost for your location from your state extension office or the local weather station record, not the earliest frost-free date in a good year. The New Hampshire guide's own advice is that Memorial Day is a conservative last-frost estimate for central New Hampshire; a grower in Georgia will use a date two months earlier. Because the whole schedule shifts with that one input, growers with a cold pocket or a warm south slope should adjust it before adjusting anything else.
What is not scheduled here
Crops the guide keys to soil temperature rather than frost, such as beets, carrots, sweet corn, and peas, are not in the preset table; add them as custom crops using your own packet guidance. Cucumbers, squash, and pumpkins can be transplanted or direct sown when soil reaches 70 F; the tool plans their sowing two weeks after the frost date as a stand-in for that soil temperature. Fall and succession plantings, which count back from the first fall frost, are outside this spring planner.
Worked example: last frost May 15
With a May 15 last frost, onions start indoors February 13 and transplant April 17. Lettuce starts March 27 and transplants April 24; broccoli starts March 27 and transplants May 1. Peppers start March 27 and tomatoes April 10, both transplanting May 29. Summer squash can start indoors May 8 for a May 29 transplant or be sown outdoors May 29, and beans are sown directly on May 15. The first job is February 13 and the last is May 29. Dates shown are for a May 15 frost date in a non-leap year.
Source
- University of New Hampshire Extension, Growing vegetables: when to plant your vegetable garden (fact sheet). Time from seed to transplant and when to set out or sow relative to the last frost by crop, for example tomato 6 to 8 weeks and 1 to 2 weeks after last frost, pepper 8 to 10 weeks and 2 weeks after, cabbage 4 to 6 weeks and 4 weeks before. Accessed Sep 4, 2026.
This calculator gives planning estimates from the numbers you enter. It is not accounting, tax, veterinary, or legal advice. Replace the defaults with your own farm records whenever you have them.
Frequently asked questions
When should I start tomato seeds indoors?
About 6 to 8 weeks before you will transplant, and transplant 1 to 2 weeks after your average last frost, per UNH Extension. For a May 15 last frost that is a late-May transplant and an indoor start around April 10. Peppers start two weeks earlier and eggplant about a week earlier, because eggplant also goes out a week later.
How do I find my last frost date?
Ask your county extension office or look up the average last spring frost for the nearest weather station. Use the average, not the earliest, and shift it later for a frost pocket or an exposed site. Every date in the calculator moves with it.
Which vegetables can be planted before the last frost?
Cabbage, kale, onions, and leeks can be set out about 4 weeks before; lettuce and spinach about 3 weeks before; broccoli, cauliflower, and Swiss chard about 2 weeks before. Radish and turnip seed can go in the ground 2 to 4 weeks before the last frost.
Can I direct sow squash and cucumbers instead of transplanting?
Yes. UNH Extension lists both: 3 to 4 weeks indoors and set out 2 weeks after last frost, or sow in the garden when soil reaches 70 F. The calculator shows both dates and uses two weeks after the frost date as the sowing target.
Does this calculator do fall planting?
No. Fall crops count back from the first fall frost using days to maturity, and the source guide covers spring only. Use it for the spring plan and your packet's days to maturity for fall succession sowings.
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