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Frost and Seed

Spring Planting Planner: When to Start Seeds and Plant Out

Updated

Figures checked against their sources on ; next check .

Photograph of young tomato transplants just set into a freshly prepared spring garden bed beside a trowel

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When to plant vegetables in spring, counted from the last frost (UNH Extension)
CropWeeks indoors before setting outSet out transplantsSow or plant in the garden
Basil (start indoors)6 to 8 weeks2 weeks after the last frost—
Bean——After the last frost
Beet——When the soil reaches 45 °F
Broccoli4 to 6 weeks2 to 4 weeks before the last frost—
Brussels Sprout (start indoors)4 to 6 weeks2 to 4 weeks before the last frost—
Cabbage (start indoors)4 to 6 weeks4 weeks before the last frost—
Carrot——When the soil reaches 60 °F
Cauliflower (start indoors)4 to 6 weeks2 weeks before the last frost—
Celery (start indoors)10 to 12 weeksAfter the last frost—
Corn——When the soil reaches 60 °F
Cucumber3 to 4 weeks1 to 2 weeks after the last frostWhen the soil reaches 70 °F
Eggplant (start indoors)8 to 10 weeks2 to 3 weeks after the last frost—
Kale4 to 6 weeks4 weeks before the last frost—
Kohlrabi4 to 6 weeks4 weeks before the last frost—
Leek (start indoors)8 to 10 weeks4 weeks before the last frost—
Lettuce4 to 5 weeks3 to 4 weeks before the last frost—
Melon (start indoors)3 to 4 weeks2 weeks after the last frost—
Onion (start indoors)8 to 10 weeks4 weeks before the last frost—
Parsley (start indoors)9 to 10 weeks2 to 3 weeks before the last frost—
Parsnip——After the last frost
Pea——As soon as the soil thaws
Pepper (start indoors)8 to 10 weeks2 weeks after the last frost—
Potato——Seed potatoes: 1 to 2 weeks before the last frost
Pumpkin3 to 4 weeks2 weeks after the last frostWhen the soil reaches 70 °F
Radish——2 to 4 weeks before the last frost
Rutabaga——Mid-June to mid-July (UNH's dates for New Hampshire)
Spinach4 to 6 weeks3 to 6 weeks before the last frost—
Summer Squash3 to 4 weeks2 weeks after the last frostWhen the soil reaches 70 °F
Sweetpotato——Slips: 1 to 2 weeks after the last frost
Swiss Chard4 to 6 weeks2 weeks before the last frost4 weeks before the last frost
Tomato (start indoors)6 to 8 weeks1 to 2 weeks after the last frost—
Turnip——2 to 4 weeks before the last frost
Winter Squash3 to 4 weeks2 weeks after the last frostWhen the soil reaches 70 °F
Zucchini3 to 4 weeks2 weeks after the last frostWhen the soil reaches 70 °F

In short: Pick your weather station or type a ZIP code. For each vegetable on UNH Extension's planting list you get the day range to start seeds indoors, to set out transplants and to sow in the garden, counted from your own last spring frost, either the typical date or the later, safer one.

The rule behind the dates

Spring planting starts from one date: the last frost. The University of New Hampshire's Cooperative Extension puts it first in its fact sheet on when to plant: determine the last frost date for your area, and do not seed or transplant frost-sensitive plants before it. Every other date follows from that one. Cabbage goes out a few weeks before it, tomatoes a week or two after, and seeds started indoors are counted back from the day their transplants go out.

UNH's list gives that timing for 34 vegetables and herbs, and this planner reads it as published. UNH marks 12 of them to start indoors and set out as transplants. For many others it gives both a transplant timing and a way to sow directly in the garden, and for a few, such as carrots, corn and squash, it names a soil temperature to wait for instead of a date.

Where your last frost comes from

The fact sheet was written for New Hampshire, where it calls Memorial Day a conservative last frost estimate for the center of the state. This planner swaps in your own date: the last spring frost from NOAA's climate normals at the weather station you choose. You can count from the typical date, which half of springs beat, or from the late date that only one spring in ten goes past. The late date is the default because a transplant killed by frost costs more than one planted a week late.

Worked example: tomatoes near Minneapolis

At the Minneapolis-St Paul airport station, the typical last frost is April 23, and one year in ten still has a frost on or after May 7. UNH says tomatoes take 6 to 8 weeks from sowing to transplant and are safe to set out 1 to 2 weeks after the last frost.

Counting from the late date, the tomatoes go out between May 14 to May 21. For the seeds, UNH's own example counts back the longer figure, 8 weeks, from the planting day, so they are sown indoors between March 19 to April 2: the earlier day for the earliest planting, the later one if you want to keep the seedlings indoors for the shortest time. Counting from the typical date instead moves the planting earlier, to April 30 to May 7, and leaves an even chance of a frost still to come.

Cabbage runs the other way. UNH sets it out 4 weeks before the last frost, which puts it in the ground around March 26 against the typical date. Peas go in as soon as the soil thaws.

Soil temperature instead of a date

For crops that UNH times by soil warmth, the planner shows the temperature rather than inventing a date: 45 °F for beets, 60 °F for carrots and corn, and 70 °F for cucumbers, pumpkins and squash sown in the garden. A soil thermometer answers that better than any calendar; the soil temperature chart gives each crop's range and how to take a reading.

Before you plant

These are long-term odds, not a forecast, so check the coming week's weather before the tender crops go out, and harden off indoor seedlings first; the hardening off checklist walks through it. The University of Minnesota gives its own indoor weeks in the seed starting schedule, and they do not always match UNH's. UNH's fact sheet carries no publication date. If you would rather start from your own state's calendar, the state planting pages copy each extension service's dates for a crop, region by region, and set them beside frost dates for that state's cities.