Seed Starting Date Calculator

Tell it your last frost date and what you're growing, and it counts back to the perfect day to start seeds indoors.

📖 How it works & FAQ

Last spring frost date

Crop

—Start seeds indoorspick your frost date

—Transplant outdoors

—Weeks growing indoors

Time your seeds to the frost, not the calendar

The single biggest mistake in starting seeds is sowing too early. Seedlings that outgrow their trays before it's safe to plant out get leggy, root-bound and stressed. This calculator flips the problem around: it starts from your last spring frost date and counts backward the right number of weeks for each crop, so your transplants are the perfect size when the weather finally cooperates.

How the weeks-before-frost math works

Every crop has a known indoor head start. Warm-season plants like tomatoes (6–8 weeks), peppers and eggplant (8 weeks) need a long runway and go outside after frost. Cool-season crops like brassicas (4–6 weeks), lettuce, kale and onions tolerate a chill and can transplant before your last frost. The tool subtracts the start weeks from your frost date to get the sow date, then shifts the frost date to get a safe transplant window. Dates are estimates to plan around, not a guarantee against a late cold snap.

How to use it

Find your average last spring frost date (search your ZIP or postal code plus "last frost date").
Enter that date in the first field.
Pick the crop you're growing from the list.
Read your indoor sow date, transplant date and weeks-indoors instantly — no button needed.

FAQ

Where do I find my last frost date?: Local extension offices and almanac sites list it by ZIP or postal code. Use the average "50% chance" date, then add a week of caution if you get late frosts.
Why do some crops transplant before the frost date?: Hardy crops like kale, cabbage and onions shrug off light frost, so they can go out a few weeks early. Frost-tender crops like tomatoes and basil must wait until after the date.
Can I start seeds earlier for a bigger head start?: Usually no — earlier means overgrown, root-bound seedlings. Stick close to the recommended window unless you can pot up into larger containers.
Does this account for my grow lights or greenhouse?: It assumes standard indoor starting. A heated greenhouse can let you nudge transplant dates earlier; a cold windowsill may push them later.